EP0349387A1 - Indirectly heated X-ray tube with a flat cathode - Google Patents

Indirectly heated X-ray tube with a flat cathode Download PDF

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Publication number
EP0349387A1
EP0349387A1 EP89401761A EP89401761A EP0349387A1 EP 0349387 A1 EP0349387 A1 EP 0349387A1 EP 89401761 A EP89401761 A EP 89401761A EP 89401761 A EP89401761 A EP 89401761A EP 0349387 A1 EP0349387 A1 EP 0349387A1
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EP
European Patent Office
Prior art keywords
cathode
tube according
anode
plane
tube
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Granted
Application number
EP89401761A
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German (de)
French (fr)
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EP0349387B1 (en
Inventor
Sixte De Fraguier
Gilles Lemestreallan
François Caire
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General Electric CGR SA
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General Electric CGR SA
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    • 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
    • H01J35/06—Cathodes
    • 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
    • H01J35/06—Cathodes
    • H01J35/064—Details of the emitter, e.g. material or structure
    • 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
    • H01J35/06—Cathodes
    • H01J35/066—Details of electron optical components, e.g. cathode cups
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H01J35/147—Spot size control

Definitions

  • the present invention relates to an X-ray tube which can be used in particular in the medical field.
  • the main characteristics of these tubes are their resistance to the drift of their emission characteristics as a function of their temperature as well as the homogeneity and the X-ray illumination produced by all the points of their focus.
  • the invention aims to improve such tubes by avoiding their possible destruction under the effect of excessive heating of their anode or their cathode.
  • X-rays are produced by electron bombardment, in a vacuum enclosure, of a target made from a material with a high atomic number.
  • the electrons necessary for the bombardment of this target are released by thermoelectronic effect, generally in a helical filament of tungsten, from a cathode placed precisely within a room of concentration.
  • the concentration piece plays a focusing role at the same time as a Wehnelt role.
  • the target constitutes an anode of the tube.
  • the initial velocities of the electrons at the level of the emitter are very dispersed. Their trajectory therefore has a disordered structure and the focusing system is responsible for correcting them.
  • the focusing system is generally not efficient enough. Consequently, instead of the impact of the bombardment electrons on the target, we obtain a rather complicated tangle of trajectories. This gives the X-ray thermal focus a rather unfavorable energy profile with a good image quality.
  • the transmitter consists of a beam.
  • this beam is hollow, and possibly of substantially rectangular section.
  • the rigidity of a beam being much greater than the rigidity of a ribbon.
  • the beam is hollow. For a given heating power this reduces the ignition time of the tube.
  • the hollow beam is even traversed right through by a heating helical filament: the beam is heated by indirect heating. This indirect heating may even be focused only on predetermined parts of the beam, in particular the face of the beam opposite the anode. This further limits the heating power.
  • the subject of the invention is therefore an X-ray tube provided with a cathode and an anode, facing the cathode, for emitting X-radiation, the cathode being a planar cathode, characterized in that this cathode comprises a beam.
  • a cathode 1 has the appearance of a beam shown in perspective in Figure 1.
  • This beam is prismatic, hollow, and has substantially the appearance of a house.
  • the base of the house constitutes an emissive face 7 of the cathode, the walls of the house such as the wall 23 have windows such as 24.
  • the advantage of manufacturing a hollow beam lies in the reduction of the quantity of metal to heat. If this quantity is lower, the thermal inertia of the cathode will be less, the starting of the tube could be faster. Furthermore, the consumption of the cathode heating supply can be reduced, which is an advantage when we know the insulation problems which must be faced with the heating circuits of such cathodes.
  • this cathode could be envisaged by passing an electric current directly through it, it is preferred to use a heating filament 25 for example of the same type as the filaments used in the prior art as a transmitter.
  • This heated filament is brought to a negative high voltage (several thousand volts) relative to the cathode.
  • the beam cathode is made of tungsten.
  • the ceiling 26 and the interior of the walls thereof are provided with a mattress 27 of insulating fibers to concentrate the heating on the emissive part of the cathode. .
  • the fibers are ceramic fibers which allow good insulation of the internal walls of the house.
  • This bombardment is limited to the front wall 33.
  • this front wall has a concave profile 33.
  • this concave profile is even so concave that the wings respectively 29 and 30 of this cathode have internal faces, respectively 31 and 32, closer to the filament 25 than is the internal face of the cathode at the place 33 from its middle. In this way the wings which are both thicker and which would be harder to heat are however more heated.
  • the base 7 of the beam is brought at all points to a substantially constant temperature, it emits with a substantially constant flow the expected electron radiation.
  • the beam according to the invention now has the advantage that its emissive face 7 no longer distorts under the effects of heating, it nevertheless undergoes expansions which should be guided without upsetting them.
  • the cathode is fixed by a lug 34 constituting in a way the chimney of the house.
  • the method of attachment is preferably obtained by blocking this tab 34 between two screws 35 and 36 which come to grip it between them respectively.
  • This mounting at a fixing point has the advantage of leaving the cathode all the desired degrees of freedom. It is in particular preferable to a method of fixing with two points which would have the drawback that the reactions between these two points would inevitably have repercussions on the flatness of the emissive surface 7.
  • the walls of this cathode are held in a focal room 8 by ceramic pieces such as 37 and 38 which come to rest on either side on it. This makes it possible to avoid any phenomenon of bending or vibration harmful to an exact positioning of the transmitter in the focusing part.
  • the pins allow the transmitter to thermally expand along its greatest length while keeping it laterally in its reference position.
  • the electrical supply of the cathode can be obtained by passing the high voltage through the screws 35 or 36.
  • FIG. 3 schematically shows an X-ray tube provided with a cathode-beam 1 according to the invention.
  • This X-ray tube comprises, in an empty enclosure, not shown, the cathode 1 located opposite an anode 2.
  • the anode receives electronic radiation 3 on its focus 4 and re-emits X-ray radiation 5 in particular in the direction of a usage window 6.
  • the usage window is part of the tube casing.
  • the cathode has the particularity of opposing a planar face 7 opposite the anode 2. It also has the particularity of being inserted into a focusing optic 8 known as on.
  • This walking focusing optic is to create a distribution of the electric field between the anode and the cathode such that the radiation 3 of the electrons is of the convergent type.
  • the focusing device 8 can also being a single step, we found here more advantageous to make it double step.
  • the focusing piece 8 has a straight prismatic shape of which FIG. 3 represents the plane of straight section.
  • the part 8 comprises the two steps, respectively 9 and 10 distributed symmetrically in 9 ′ and 10 ′ on either side of the cathode 1.
  • Each step has a step 91 or 101 and a riser 92 or 102. (respectively 91 ′ 92 ′ 101 ′ 102 ′).
  • the plane 7 of the cathode 1 is distant from the anode 2 by a distance of approximately 7.5 mm.
  • the tops 91 and 91 ′ of steps 9 and 9 ′ are spaced from the anode by about 7mm.
  • the tops 101 and 101 ′ are spaced about 6 mm from the plane of the anode 2.
  • the width of the cathode 1, measured in the plane of cross section of the focal prismatic part 8, is equal to 2 mm.
  • the width of a housing 11 where this cathode is placed inside the focal piece 8 is 2.2 mm.
  • the distance between risers 92 and 92 ′ is 4 mm while the distance between risers 101 and 102 ′ is 5 mm.
  • the device has a symmetrical appearance with respect to a plane passing through the axis 12 of the radiation, perpendicular to the plane of the figure.
  • the assembly may be circular, the axis 12 serving as an axis of revolution for the cathode as well as for the focusing part. It is possible that the anode 2 is a rotating type anode and even that it has an inclined face on the axis 12. In this case the distances indicated are rather the distances measured on this axis 12 between the plane 7 of the cathode and the trace of the axis 12 on the anode 2.
  • the thermal flux FT ( Figure 4) is then substantially constant, for a given high operating voltage, as a function of the load of the tube D.
  • the diagram of FIG. 4 presents three curves respectively 13 to 15 parameterized by high voltages respectively of 20 KV, 40 KV or 50 KV, displaying in a range of use situated between 150 Milliamperes and 500 milliamperes, a substantially flat appearance.
  • the heat flux is expressed in KW per mm2. In the example shown, it is always less than 50 KW per mm2 even for the highest operating high voltage.
  • the significance of the flat appearance of this heat flux as a function of the load simply means that the dimension 16 of the thermal focus evolves linearly with the load.
  • the increase in the dose rate causes the displacement towards the anode 2 of the point of convergence.
  • the spacing 17 18 of the lateral rays of the X-ray beam before the point of convergence conversely causes the dimension 16 of the focal point to shrink. It has been discovered that this narrowing, which could be disastrous, is in fact limited by a phenomenon of saturation of the emission of the electrons torn from the upper face 7 of the cathode 1.

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  • X-Ray Techniques (AREA)

Abstract

The problems are resolved of temperature holding of cathodes by making hollow beam-shaped flat cathodes. This ensures them a rigidity inherent in the beam-shape without however endowing them with the disadvantages of too large a thermal inertia. …<IMAGE>…

Description

La présente invention a pour objet un tube à rayons X notamment utilisable dans le domaine médical. Les principales caractéristiques de ces tubes sont leur résistance à la dérive de leurs caractéristiques d'émission en fonction de leur température ainsi que l'homogénéité et l'illumination X produite par tous les points de leur foyer. L'invention vise à perfectionner de tels tubes en évitant leur éventuelle destruction sous l'effet d'un échauffement trop important de leur anode ou de leur cathode.The present invention relates to an X-ray tube which can be used in particular in the medical field. The main characteristics of these tubes are their resistance to the drift of their emission characteristics as a function of their temperature as well as the homogeneity and the X-ray illumination produced by all the points of their focus. The invention aims to improve such tubes by avoiding their possible destruction under the effect of excessive heating of their anode or their cathode.

D'une façon générale des rayons X sont produits par le bombardement électronique, dans une enceinte à vide, d'une cible élaborée dans un matériau à haut numéro atomique. Les électrons nécessaires au bombardement de cette cible sont libérés par effet thermo-électronique, généralement dans un filament hélicoïdal de tungstène, d'une cathode placée avec précision au sein d'une pièce de concentration. La pièce de concentration joue un rôle focalisateur en même temps qu'un rôle de Wehnelt. La cible constitue une anode du tube. Dans ce type de configuration très classique, les vitesses initiales des électrons au niveau de l'émetteur sont très dispersées. Leur trajectoire présente donc une structure désordonnée et le système de focalisation est chargé de les rectifier. Le système de focalisation n'est généralement pas suffisamment performant. En conséquence au lieu de l'impact des électrons de bombardement sur la cible, on obtient un enchevêtrement assez compliqué des trajectoires. Ceci confère au foyer thermique des rayons X un profil énergétique assez peu favorable avec une bonne qualité d'image.In general, X-rays are produced by electron bombardment, in a vacuum enclosure, of a target made from a material with a high atomic number. The electrons necessary for the bombardment of this target are released by thermoelectronic effect, generally in a helical filament of tungsten, from a cathode placed precisely within a room of concentration. The concentration piece plays a focusing role at the same time as a Wehnelt role. The target constitutes an anode of the tube. In this very conventional type of configuration, the initial velocities of the electrons at the level of the emitter are very dispersed. Their trajectory therefore has a disordered structure and the focusing system is responsible for correcting them. The focusing system is generally not efficient enough. Consequently, instead of the impact of the bombardment electrons on the target, we obtain a rather complicated tangle of trajectories. This gives the X-ray thermal focus a rather unfavorable energy profile with a good image quality.

Dans des développements récents, par exemple dans ceux décrits dans la demande de brevet européen n° 85 106753.8 déposée le 31 mai 1985, on fait référence à une cathode qui n'est plus constituée par un filament mais qui est maintenant constituée par une portion d'un ruban présentant à l'émission des électrons une surface plane en face de l'anode. L'intérêt d'utiliser un émetteur d'électrons plan a déjà été présenté antérieurement à cette demande. Il consiste à maintenir une certaine cohésion des charges électroniques au cours de leur trajectoire vers la cible. En effet, l'expérience a montré qu'on obtient dans ce cas une répartition de potentiel électrostatique favorable à une meilleure focalisation des charges électriques. Le foyer X ainsi obtenu présente alors un profil énergétique pratiquement homogène, ce qui est bénéfique à la qualité de l'image. La littérature scientifique relate certaines expérimentations basées sur ce principe général. On y fait toujours usage d'émetteur élaboré sous la forme de ruban de tungstène, lesquels présentent cependant systématiquement des problèmes de tenue thermomécanique. C'est d'ailleurs pour résoudre de tels problèmes que la demande de brevet européen ci-dessus évoquée a été déposée. En particulier, malgré tous les soins portés au laminage des rubans, des phénomènes de contraintes différentielles se produisent dans ceux-ci et ils prennent du fait des échauffements et des refroidissements successifs dans le tube une allure dite en tôle ondulée. Les avantages de disposer d'un émetteur plan sont alors perdus.In recent developments, for example in those described in European patent application No. 85 106753.8 filed May 31, 1985, reference is made to a cathode which is no longer constituted by a filament but which is now constituted by a portion of '' a ribbon having on the emission of electrons a flat surface opposite the anode. The advantage of using a planar electron emitter has already been presented prior to this request. It consists in maintaining a certain cohesion of the electronic charges during their trajectory towards the target. In fact, experience has shown that an electrostatic potential distribution is obtained in this case favorable to better focusing of the electric charges. The focal point X thus obtained then has a practically homogeneous energy profile, which is beneficial to the quality of the image. The scientific literature relates certain experiments based on this general principle. There is always use of an emitter developed in the form of a tungsten ribbon, which however systematically presents thermomechanical resistance problems. It is moreover to resolve such problems that the European patent application mentioned above was filed. In particular, despite all the care taken in rolling the ribbons, phenomena of differential stresses occur in them and they take on due to the successive heating and cooling in the tube a so-called corrugated sheet shape. The advantages of having a plan transmitter are then lost.

La présente invention a pour objet de remédier à cet inconvénient en proposant un dispositif émetteur plan offrant une rigidité mécanique permettant de s'affranchir des problèmes de tôle ondulée évoqués ci-dessus. En simplifiant, l'émetteur est constitué par une poutre. De préférence cette poutre est creuse, et éventuellement de section sensiblement rectangulaire. On bénéficie alors de tous les avantages conférés par la rigidité d'une poutre, cette rigidité étant bien supérieure à la rigidité d'un ruban. En outre, pour éviter d'avoir à chauffer une trop grosse masse de matériau, la poutre est creuse. Pour une puissance de chauffage donnée ceci réduit le temps d'allumage du tube. Dans un perfectionnement la poutre creuse est même traversée de part en part par un filament hélicoïdal chauffant : la poutre est chauffée par chauffage indirect. Ce chauffage indirect peut même n'être focalisé que sur des parties prédéterminées de la poutre, notamment la face de la poutre en regard de l'anode. Ceci permet encore de limiter la puissance de chauffage.The object of the present invention is to remedy this drawback by proposing a flat emitting device offering mechanical rigidity making it possible to to get rid of the corrugated sheet problems mentioned above. To simplify, the transmitter consists of a beam. Preferably this beam is hollow, and possibly of substantially rectangular section. We then benefit from all the advantages conferred by the rigidity of a beam, this rigidity being much greater than the rigidity of a ribbon. In addition, to avoid having to heat too large a mass of material, the beam is hollow. For a given heating power this reduces the ignition time of the tube. In an improvement, the hollow beam is even traversed right through by a heating helical filament: the beam is heated by indirect heating. This indirect heating may even be focused only on predetermined parts of the beam, in particular the face of the beam opposite the anode. This further limits the heating power.

L'invention a donc pour objet un tube radiogène muni d'une cathode et d'une anode, en regard de la cathode, pour émettre un rayonnement X, la cathode étant une cathode plane, caractérisé en ce que cette cathode comporte une poutre.The subject of the invention is therefore an X-ray tube provided with a cathode and an anode, facing the cathode, for emitting X-radiation, the cathode being a planar cathode, characterized in that this cathode comprises a beam.

L'invention sera mieux comprise à la lecture de la description qui suit et à l'examen des figures qui l'accompagnent. Celles-ci ne sont données qu'à titre indicatif et nullement limitatif de l'invention. Les figures montrent :

  • - figure 1 : une vue en perspective d'une cathode en poutre selon l'invention,
  • - figure 2 : une vue en coupe de la cathode de la figure 1
  • - figure 3 : une coupe schématique d'un tube radiogène muni d'une poutre selon l'invention;
  • - figures 4 et 5 : des diagrammes énergétiques pour le tube de la figure 3 ;
The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are given for information only and in no way limit the invention. The figures show:
  • FIG. 1: a perspective view of a beam cathode according to the invention,
  • - Figure 2: a sectional view of the cathode of Figure 1
  • - Figure 3: a schematic section of an X-ray tube provided with a beam according to the invention;
  • - Figures 4 and 5: energy diagrams for the tube of Figure 3;

Dans l'invention une cathode 1 a l'allure d'une poutre représentée en perspective sur la figure 1. Cette poutre est prismatique , creuse, et a sensiblement l'allure d'une maison. La base de la maison constitue une face 7 émissive de la cathode, les murs de la maison tels que le mur 23 possèdent des fenêtres telles que 24. L'intérêt de fabriquer une poutre creuse se situe dans la réduction de la quantité de métal à chauffer. Si cette quantité est plus faible, l'inertie thermique de la cathode sera moins grande, le démarrage du tube pourra être plus rapide. Par ailleurs la consommation de l'alimentation de chauffage de la cathode pourra être réduite ce qui est un avantage quand on sait les problèmes d'isolement auxquels doivent être confrontés les circuits de chauffage de telles cathodes.In the invention a cathode 1 has the appearance of a beam shown in perspective in Figure 1. This beam is prismatic, hollow, and has substantially the appearance of a house. The base of the house constitutes an emissive face 7 of the cathode, the walls of the house such as the wall 23 have windows such as 24. The advantage of manufacturing a hollow beam lies in the reduction of the quantity of metal to heat. If this quantity is lower, the thermal inertia of the cathode will be less, the starting of the tube could be faster. Furthermore, the consumption of the cathode heating supply can be reduced, which is an advantage when we know the insulation problems which must be faced with the heating circuits of such cathodes.

Bien qu'on pourrait envisager un chauffage direct de cette cathode en faisant passer un courant électrique directement au travers de celle-ci, on préfère utiliser un filament de chauffage 25 par exemple du même type que les filaments utilisés dans l'état de la technique comme émetteur. Ce filament chauffé est porté à une haute tension négative (de plusieurs milliers de volts) par rapport à la cathode. Dans un exemple préféré la cathode en poutre est réalisée en tungstène. Afin de limiter également la quantité d'énergie thermique à fournir pour chauffer la cathode on munit le plafond 26 et l'intérieur des murs de celle-ci d'un matelas 27 de fibres isolantes pour concentrer le chauffage sur la partie émissive de la cathode. Dans un exemple les fibres sont des fibres de céramique qui permettent un bon isolement des parois internes de la maison. Les électrons émis par le filament chauffant bombardent alors l'arrière de la cathode selon un dessin représenté par les courbes de champ électrique 28. Ce bombardement est limité à la paroi avant 33. Par ailleurs cette paroi avant présente un profil 33 concave. Dans un exemple préféré ce profil concave est même tellement concave que des ailes respectivement 29 et 30 de cette cathode présentent des faces intérieures, respectivement 31 et 32, plus proches du filament 25 que ne l'est la face intérieure de la cathode à l 'endroit 33 de son milieu. De cette manière les ailes qui sont à la fois plus épaisses et qui seraient plus dures à chauffer sont cependant plus chauffées. De cette manière la base 7 de la poutre est porté en tous points à une température sensiblement constante, il émet avec un débit sensiblement constant le rayonnement d'électrons attendu.Although direct heating of this cathode could be envisaged by passing an electric current directly through it, it is preferred to use a heating filament 25 for example of the same type as the filaments used in the prior art as a transmitter. This heated filament is brought to a negative high voltage (several thousand volts) relative to the cathode. In a preferred example, the beam cathode is made of tungsten. In order also to limit the amount of thermal energy to be supplied to heat the cathode, the ceiling 26 and the interior of the walls thereof are provided with a mattress 27 of insulating fibers to concentrate the heating on the emissive part of the cathode. . In one example, the fibers are ceramic fibers which allow good insulation of the internal walls of the house. The electrons emitted by the heating filament bombard then the rear of the cathode according to a drawing represented by the electric field curves 28. This bombardment is limited to the front wall 33. Furthermore this front wall has a concave profile 33. In a preferred example, this concave profile is even so concave that the wings respectively 29 and 30 of this cathode have internal faces, respectively 31 and 32, closer to the filament 25 than is the internal face of the cathode at the place 33 from its middle. In this way the wings which are both thicker and which would be harder to heat are however more heated. In this way the base 7 of the beam is brought at all points to a substantially constant temperature, it emits with a substantially constant flow the expected electron radiation.

Bien que la poutre selon l'invention présente maintenant l'intérêt que sa face émissive 7 ne se distorde plus sous les effets des échauffements, elle subit cependant des dilatations qu'il convient de guider sans les contrarier. Dans ce but la cathode est fixée par une patte 34 constituant en quelque sorte la cheminée de la maison. Le mode de fixation est de préférence obtenu par blocage de cette patte 34 entre deux vis 35 et 36 qui viennent l'enserrer entre elles respectivement. Ce montage à un point de fixation présente l'avantage de laisser à la cathode tous les degrés de liberté voulus. Il est en particulier préférable à un mode de fixation avec deux points qui présenterait l'inconvénient que les réactions entre ces deux points se répercuteraient immanquablement sur la planéïté de la surface émissive 7. Pour guider les déplacements de la cathode avec la température, les murs de cette cathode sont maintenus dans une pièce focale 8 par des pions de céramique tels que 37 et 38 qui viennent s'appuyer de part et d'autre sur elle. Ceci permet d'éviter tout phénomène de flexion ou de vibration néfaste à un exact positionnement de l'émetteur dans la pièce de focalisation. Les pions permettent à l'émetteur de se dilater thermiquement suivant sa plus grande longueur tout en le maintenant latéralement dans sa position de référence. En pratique, l'alimentation électrique de la cathode peut être obtenu en faisant passer la haute tension par les vis 35 ou 36.Although the beam according to the invention now has the advantage that its emissive face 7 no longer distorts under the effects of heating, it nevertheless undergoes expansions which should be guided without upsetting them. For this purpose the cathode is fixed by a lug 34 constituting in a way the chimney of the house. The method of attachment is preferably obtained by blocking this tab 34 between two screws 35 and 36 which come to grip it between them respectively. This mounting at a fixing point has the advantage of leaving the cathode all the desired degrees of freedom. It is in particular preferable to a method of fixing with two points which would have the drawback that the reactions between these two points would inevitably have repercussions on the flatness of the emissive surface 7. To guide the movements of the cathode with temperature, the walls of this cathode are held in a focal room 8 by ceramic pieces such as 37 and 38 which come to rest on either side on it. This makes it possible to avoid any phenomenon of bending or vibration harmful to an exact positioning of the transmitter in the focusing part. The pins allow the transmitter to thermally expand along its greatest length while keeping it laterally in its reference position. In practice, the electrical supply of the cathode can be obtained by passing the high voltage through the screws 35 or 36.

La figure 3 montre schématiquement un tube radiogène muni d'une cathode-poutre 1 selon l'invention. Ce tube radiogène comporte, dans une enceinte vide non représentée, la cathode 1 située en vis à vis d'une anode 2. L'anode reçoit un rayonnement électronique 3 sur son foyer 4 et réémet un rayonnement X 5 notamment en direction d'une fenêtre d'utilisation 6. La fenêtre d'utilisation fait partie de l'enveloppe du tube. Selon l'invention la cathode présente la particularité d'opposer une face plane 7 en vis à vis de l'anode 2. Elle présente en outre la particularité d'être insérée dans une optique de focalisation 8 dite à marche. Cette optique de focalisation à marche a pour objet de créer une répartition du champ électrique entre l'anode et la cathode telle que le rayonnement 3 des électrons soit du type convergent. On distingue deux types de rayonnement convergent. Dans un premier type, représenté sur la figure 3, le point de convergence des électrons est situé derrière le plan de l'anode : il est virtuel. Dans ce cas, le rayonnement est dit direct. Dans un deuxième type de rayonnement, dit croisé, le point de convergence des électrons se situe en position intermédiaire entre la cathode 7 et l'anode 2 : il est réel.FIG. 3 schematically shows an X-ray tube provided with a cathode-beam 1 according to the invention. This X-ray tube comprises, in an empty enclosure, not shown, the cathode 1 located opposite an anode 2. The anode receives electronic radiation 3 on its focus 4 and re-emits X-ray radiation 5 in particular in the direction of a usage window 6. The usage window is part of the tube casing. According to the invention, the cathode has the particularity of opposing a planar face 7 opposite the anode 2. It also has the particularity of being inserted into a focusing optic 8 known as on. The purpose of this walking focusing optic is to create a distribution of the electric field between the anode and the cathode such that the radiation 3 of the electrons is of the convergent type. There are two types of convergent radiation. In a first type, represented in FIG. 3, the point of convergence of the electrons is located behind the plane of the anode: it is virtual. In this case, the radiation is said to be direct. In a second type of radiation, called cross, the point of convergence of the electrons is located in the intermediate position between the cathode 7 and the anode 2: it is real.

Bien que le dispositif de focalisation 8 puisse être également à simple marche, on a trouvé ici plus avantageux de le réaliser à double marche. La pièce de focalisation 8 a une forme prismatique droite dont la figure 3 représente le plan de section droit. La pièce 8 comporte les deux marches, respectivement 9 et 10 réparties symétriquement en 9′ et 10′ de part et d'autre de la cathode 1. Chaque marche comporte un dessus de marche 91 ou 101 et une contremarche 92 ou 102. (respectivement 91′ 92′ 101′ 102′). Dans un exemple préféré de réalisation le plan 7 de la cathode 1 est distant de l'anode 2 d'une distance d'environ 7.5 mm. Les dessus 91 et 91′ des marches 9 et 9′ sont distants de l'anode d'environ 7mm. Les dessus, 101 et 101′ sont distants eux d'environ 6 mm du plan de l'anode 2. La largeur de la cathode 1, mesurée dans le plan de section droite de la pièce prismatique focale 8, vaut 2 mm. La largeur d'un logement 11 où est placée cette cathode à l'intérieur de la pièce focale 8 vaut 2.2 mm. La distance qui sépare les contremarches 92 et 92′ est de 4 mm tandis que la distance qui sépare les contremarches 101 et 102′ est de 5 mm. De préférence le dispositif a une allure symétrique par rapport à un plan passant par l'axe 12 du rayonnement, perpendiculairement au plan de la figure. En variante cependant, plutôt que d'être prismatique, l'ensemble peut être circulaire l'axe 12 servant d'axe de révolution à la cathode ainsi qu'à la pièce de focalisation. Il est possible que l'anode 2 soit une anode de type tournant et même qu'elle présente une face inclinée sur l'axe 12. Dans ce cas les distances indiquées sont plutôt les distances mesurées sur cet axe 12 entre le plan 7 de la cathode et la trace de l'axe 12 sur l'anode 2.Although the focusing device 8 can also being a single step, we found here more advantageous to make it double step. The focusing piece 8 has a straight prismatic shape of which FIG. 3 represents the plane of straight section. The part 8 comprises the two steps, respectively 9 and 10 distributed symmetrically in 9 ′ and 10 ′ on either side of the cathode 1. Each step has a step 91 or 101 and a riser 92 or 102. (respectively 91 ′ 92 ′ 101 ′ 102 ′). In a preferred embodiment, the plane 7 of the cathode 1 is distant from the anode 2 by a distance of approximately 7.5 mm. The tops 91 and 91 ′ of steps 9 and 9 ′ are spaced from the anode by about 7mm. The tops 101 and 101 ′ are spaced about 6 mm from the plane of the anode 2. The width of the cathode 1, measured in the plane of cross section of the focal prismatic part 8, is equal to 2 mm. The width of a housing 11 where this cathode is placed inside the focal piece 8 is 2.2 mm. The distance between risers 92 and 92 ′ is 4 mm while the distance between risers 101 and 102 ′ is 5 mm. Preferably, the device has a symmetrical appearance with respect to a plane passing through the axis 12 of the radiation, perpendicular to the plane of the figure. As a variant, however, rather than being prismatic, the assembly may be circular, the axis 12 serving as an axis of revolution for the cathode as well as for the focusing part. It is possible that the anode 2 is a rotating type anode and even that it has an inclined face on the axis 12. In this case the distances indicated are rather the distances measured on this axis 12 between the plane 7 of the cathode and the trace of the axis 12 on the anode 2.

Les dimensions données ci-dessus présentent l'avantage que le flux thermiques FT (figure 4) est alors sensiblement constant, pour une haute tension d'utilisation donnée, en fonction de la charge du tube D. En effet, le diagramme de la figure 4 présente trois courbes respectivement 13 à 15 paramétrées par des hautes tensions respectivement de 20 KV, 40 KV ou 50 KV, affichant dans une plage d'utilisation située entre 150 Milliampères et 500 milliampères, une allure sensiblement plate. Le flux thermique est exprimé en KW par mm². Dans l'exemple indiqué il est toujours inférieur à 50 KW par mm² même pour la haute tension d'utilisation la plus forte. La signification de l'aspect plat de ce flux thermique en fonction de la charge signifie tout simplement que la dimension 16 du foyer thermique évolue linéairement avec la charge. En effet, si la charge augmente, par exemple double, la dimension 16 augmente, et la puissance de rayon X émise augmente également, double, sans provoquer localement de contraintes thermiques anormales sur l'anode. Cette augmentation de la charge se traduit par l'écartement, selon les flèches 17 et 18, des directions latérales du rayonnement d'électrons 3. Celui-ci devient de plus en plus direct.The dimensions given above have the advantage that the thermal flux FT (Figure 4) is then substantially constant, for a given high operating voltage, as a function of the load of the tube D. In fact, the diagram of FIG. 4 presents three curves respectively 13 to 15 parameterized by high voltages respectively of 20 KV, 40 KV or 50 KV, displaying in a range of use situated between 150 Milliamperes and 500 milliamperes, a substantially flat appearance. The heat flux is expressed in KW per mm². In the example shown, it is always less than 50 KW per mm² even for the highest operating high voltage. The significance of the flat appearance of this heat flux as a function of the load simply means that the dimension 16 of the thermal focus evolves linearly with the load. Indeed, if the load increases, for example double, the dimension 16 increases, and the X-ray power emitted also increases, double, without locally causing abnormal thermal stresses on the anode. This increase in charge results in the spacing, according to arrows 17 and 18, of the lateral directions of the electron radiation 3. This becomes more and more direct.

L'avantage de la présente solution, bien que la dimension du foyer change quand la charge change, est lié au fait que l'on peut ainsi d'une manière simple disposer d'un foyer de dimension choisie. En effet, les courbes 13 à 15 sont des courbes régulières, et sans ondulation. En conséquence, en particulier en métrologie lorsque le problème du débit de dose n'est pas un point crucial, ou même en médecine lorsque les limites d'irradiation ne sont pas franchies, on peut choisir en fonction d'une netteté d'image à produire une dimension voulue du foyer. On vient ainsi de présenter un moyen simple de régler à une valeur convenable la dimension de ce foyer.The advantage of the present solution, although the size of the hearth changes when the load changes, is linked to the fact that it is thus possible in a simple manner to have a hearth of chosen dimension. Indeed, the curves 13 to 15 are regular curves, and without undulation. Consequently, in particular in metrology when the problem of the dose rate is not a crucial point, or even in medicine when the limits of irradiation are not crossed, one can choose according to a sharpness of image to produce a desired size of the fireplace. We have thus just presented a simple means of adjusting the dimension of this home.

Dans un autre exemple, où le rayonnement 3 est convergent et converge en un point de convergence placé devant l'anode, l'augmentation du débit de dose provoque le déplacement en direction de l'anode 2 du point de convergence. Dans ce rayonnement de type croisé l'écartement 17 18 des rayons latéraux du faisceau de rayonnement X avant le point de convergence provoque d'une manière inverse le rétrécissement de la dimension 16 du foyer. On a découvert que ce rétrécissement, qui pourrait être désastreux, est en fait limité par un phénomène de saturation de l'émission des électrons arrachés de la face supérieure 7 de la cathode 1. En effet, du fait de la concentration, la charge d'espace, qui a naturellement tendance à augmenter avec la charge du tube (il y a plus d'électrons) augmente à un point tel qu'elle constitue, dans certaines conditions, un écran pour l'émission des électrons suivants. En quelque sorte cette charge d'espace agit comme une grille. On a découvert que ce phénomène pouvait être utilisé comme une auto-régulation, à condition de choisir une optique de focalisation particulière. Cette optique de focalisation est du même type que celle décrite ci dessus. Elle comporte des marches. Comme précédemment ce phénomène présente l'avantage de se produire quelle que soit la haute tension d'utilisation du tube. D'une manière compréhensible, ce phénomène de saturation provoque un flux thermique à saturation sur le foyer dont la valeur dépend de cette haute tension. En effet, si la haute tension est faible, les électrons sont relativement moins accélérés. La charge d'espace de saturation se fait plus rapidement sentir : l'embouteillage de saturation se provoque d'autant plus que les électrons vont moins vite. Il est par ailleurs intéressant de remarquer que des courbes 20 à 22 (figure 5), montrant les différents effets sur le flux thermique de ce phénomène de saturation, sont bornées à l'approche de la saturation. Ceci signifie, qu'au moment de la saturation le débit ne peut plus augmenter, mais surtout le flux thermique ne peut plus augmenter. En choisissant correctement les matériaux d'anode et de cathode ou les conditions d'utilisation des tubes de telle façon que le point de saturation ne soit pas situé hors des tolérances de fonctionnement on obtient le résultat recherché.In another example, where the radiation 3 is convergent and converges at a point of convergence placed in front of the anode, the increase in the dose rate causes the displacement towards the anode 2 of the point of convergence. In this cross-type radiation, the spacing 17 18 of the lateral rays of the X-ray beam before the point of convergence conversely causes the dimension 16 of the focal point to shrink. It has been discovered that this narrowing, which could be disastrous, is in fact limited by a phenomenon of saturation of the emission of the electrons torn from the upper face 7 of the cathode 1. In fact, due to the concentration, the charge d space, which naturally tends to increase with the charge of the tube (there are more electrons) increases to such an extent that it constitutes, under certain conditions, a screen for the emission of the following electrons. In a way, this charge of space acts like a grid. It has been discovered that this phenomenon can be used as a self-regulation, provided that a particular focusing optic is chosen. This focusing optic is of the same type as that described above. It has steps. As before, this phenomenon has the advantage of occurring regardless of the high operating voltage of the tube. Understandably, this saturation phenomenon causes a saturated heat flux over the hearth, the value of which depends on this high voltage. Indeed, if the high voltage is low, the electrons are relatively less accelerated. The charge of saturation space is felt more quickly: the congestion of saturation occurs all the more as the electrons go slower. It is also interesting to note that curves 20 to 22 (figure 5), showing the different effects on the heat flow of this saturation phenomenon, are limited to the approach of saturation. This means that at the time of saturation the flow can no longer increase, but above all the heat flow can no longer increase. By correctly choosing the anode and cathode materials or the conditions of use of the tubes so that the saturation point is not located outside the operating tolerances, the desired result is obtained.

Claims (10)

1 - Tube radiogène muni d'une cathode (1) et d'une anode (2), en regard de la cathode, pour émettre un rayonnement X (3), la cathode étant une cathode plane (7) conformée comme une poutre, caractérisé en ce que la poutre est creuse (24).1 - X-ray tube provided with a cathode (1) and an anode (2), facing the cathode, for emitting X-radiation (3), the cathode being a flat cathode (7) shaped like a beam, characterized in that the beam is hollow (24). 2 - Tube selon la revendication 1 caractérisé en ce que la cathode est chauffée par un dispositif (25) de chauffage indirect.2 - Tube according to claim 1 characterized in that the cathode is heated by a device (25) for indirect heating. 3 - Tube selon la revendication 2 caractérisé en ce que le dispositif de chauffage comporte un matelas (27) de fibres pour concentrer le chauffage sur la partie émissive de la cathode.3 - Tube according to claim 2 characterized in that the heating device comprises a mattress (27) of fibers to concentrate the heating on the emissive part of the cathode. 4 - Tube selon la revendication 2 ou la revendication 3 caractérisé en ce qu'une face interne de la cathode, opposée à la face plane, a une forme concave avec des ailes (29,30) plus proches du dispositif de chauffage qu'une partie centrale interne (33) de cette forme concave.4 - Tube according to claim 2 or claim 3 characterized in that an internal face of the cathode, opposite the flat face, has a concave shape with wings (29,30) closer to the heating device than internal central part (33) of this concave shape. 5 - Tube selon l'une quelconque des revendications 1 à 4, caractérisé en ce qu'au moins une des parois (23) de la poutre comporte un évidement (24).5 - Tube according to any one of claims 1 to 4, characterized in that at least one of the walls (23) of the beam has a recess (24). 6 - Tube selon l'une quelconque des revendications 1 à 5 caractérisé en ce que cette poutre est fixée au tube par un seul point (34) de fixation6 - Tube according to any one of claims 1 to 5 characterized in that this beam is fixed to the tube by a single point (34) of fixing 7 - Tube selon l'une quelconque des revendications 1 à 6 caractérisé en ce que la poutre est guidée par des pions (37,38) de céramique fixés de part et d'autre d'elle sur un dispositif (8) de focalisation.7 - Tube according to any one of claims 1 to 6 characterized in that the beam is guided by pins (37,38) of ceramic fixed on either side of it on a device (8) for focusing. 8 - Tube selon l'une quelconque des revendications 1 à 7 caractérisé en ce que
- la cathode est une cathode plane
- placée à la base d'un dispositif de focalisation à marche.8 - Tube according to any one of claims 1 to 7 characterized in that
- the cathode is a flat cathode
- placed at the base of a walking focusing device. 9 - Tube selon la revendication 8 caractérisé en ce que le dispositif de focalisation est à double marche.9 - Tube according to claim 8 characterized in that the focusing device is dual step. 10 - Tube selon la revendication 9 caractérisé en ce que
- le plan (7) de la cathode est éloigné d'environ 7,5 mm de l'anode 2,
- le dispositif de focalisation comporte un plan profond commun avec le plan de la cathode, limité par un cylindre (92,92′) d'environ 4 mm de largeur,
- un plan intermédiaire (91,91′) situé à environ 7 mm de la cible et limité par un cylindre (102,102′) d'environ 5 mm de largeur, et
- un plan supérieur (101,101′) situé à environ 6 mm de la cible.10 - Tube according to claim 9 characterized in that
the plane (7) of the cathode is spaced about 7.5 mm from the anode 2,
the focusing device comprises a deep plane common with the plane of the cathode, limited by a cylinder (92.92 ′) of approximately 4 mm in width,
- an intermediate plane (91.91 ′) located approximately 7 mm from the target and limited by a cylinder (102.102 ′) approximately 5 mm in width, and
- an upper plane (101,101 ′) located approximately 6 mm from the target.
EP89401761A 1988-07-01 1989-06-22 Indirectly heated x-ray tube with a flat cathode Expired - Lifetime EP0349387B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8808962 1988-07-01
FR8808962A FR2633775B1 (en) 1988-07-01 1988-07-01 RADIOGENIC TUBE WITH FLAT CATHODE AND INDIRECT HEATING

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EP0349387A1 true EP0349387A1 (en) 1990-01-03
EP0349387B1 EP0349387B1 (en) 1991-11-27

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US7280636B2 (en) * 2003-10-03 2007-10-09 Illinois Institute Of Technology Device and method for producing a spatially uniformly intense source of x-rays
CN101529549B (en) * 2006-10-17 2014-09-03 皇家飞利浦电子股份有限公司 Emitter for X-ray tubes and heating method therefore
US20100002842A1 (en) * 2008-07-01 2010-01-07 Bruker Axs, Inc. Cathode assembly for rapid electron source replacement in a rotating anode x-ray generator
EP2377141B1 (en) * 2008-12-08 2014-07-16 Philips Intellectual Property & Standards GmbH Electron source and cathode cup thereof
US8477908B2 (en) * 2009-11-13 2013-07-02 General Electric Company System and method for beam focusing and control in an indirectly heated cathode
US9711320B2 (en) 2014-04-29 2017-07-18 General Electric Company Emitter devices for use in X-ray tubes
EP3518266A1 (en) 2018-01-30 2019-07-31 Siemens Healthcare GmbH Thermionic emission device

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FR2633775B1 (en) 1995-11-17
JP2840616B2 (en) 1998-12-24
JPH0254849A (en) 1990-02-23
FR2633775A1 (en) 1990-01-05
ES2027457T3 (en) 1992-06-01
DE68900473D1 (en) 1992-01-09
EP0349387B1 (en) 1991-11-27
US5044005A (en) 1991-08-27

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