EP0389326A1 - Beam switching X-ray tube with deflection plates - Google Patents

Beam switching X-ray tube with deflection plates Download PDF

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Publication number
EP0389326A1
EP0389326A1 EP90400622A EP90400622A EP0389326A1 EP 0389326 A1 EP0389326 A1 EP 0389326A1 EP 90400622 A EP90400622 A EP 90400622A EP 90400622 A EP90400622 A EP 90400622A EP 0389326 A1 EP0389326 A1 EP 0389326A1
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EP
European Patent Office
Prior art keywords
deflection
cathode
ray tube
electrodes
anode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP90400622A
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German (de)
French (fr)
Inventor
Bernard Cabinet Ballot-Schmit Evain
Horia Cabinet Ballot-Schmit Dumitrescu
Jean-Marie Cabinet Ballot-Schmit Fourmigue
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General Electric CGR SA
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General Electric CGR SA
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Publication date
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Publication of EP0389326A1 publication Critical patent/EP0389326A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/24—Tubes wherein the point of impact of the cathode ray on the anode or anticathode is movable relative to the surface thereof
    • H01J35/30—Tubes wherein the point of impact of the cathode ray on the anode or anticathode is movable relative to the surface thereof by deflection of the cathode ray
    • 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
    • H01J35/153—Spot position control

Definitions

  • the invention relates to an X-ray tube which is used in particular in radiology to obtain an X-ray beam which can have different directions in space.
  • This type of X-ray tube is, for example used in radiodiagnostics to scan an area to be analyzed or to obtain at least two X-ray beams having different energy characteristics and / or different angles of incidence on the area to be analyze.
  • An X-ray tube comprises, in a vacuum enclosure, a cathode made up of a heated filament which emits electrons and of a concentration device backed by the filament which focuses the electrons emitted on an anode brought to a positive potential compared to at the cathode.
  • the point of impact of the electron beam on the anode constitutes the source of X-radiation in the form of a beam.
  • deflection means are usually constituted by magnetic or electrostatic lenses which are arranged on the path of the beam or near this path between the cathode and the anode.
  • the implementation of these lenses requires a significant energy due to the high kinetic energy of the beam electrons due to their high speed due to a high potential difference between the cathode and the anode, greater than one hundred kilovolts.
  • Figure 1 schematically shows an X-ray tube of the type described in the aforementioned patent application. It comprises, in a vacuum enclosure represented by the dashed rectangle 11, a filament 12, a concentration device 13 attached to the filament 12 and an anode 14.
  • the filament 12 and the concentration device 13 constitute a cathode C1.
  • the concentration device 13 consists of a first metal part 15 and a second metal part 16 which are electrically insulated from each other by an insulating partition 17 secured to an insulating base 18.
  • the metal parts 15 and 16 are arranged symmetrically on either side of the filament 12 with respect to a plane of symmetry perpendicular to the plane of Figure 1. This plane of symmetry contains the axis of the filament 12 perpendicular to the plane of Figure 1 and is perpendicular at the base 18. The intersection of this plane of symmetry with the plane of Figure 1 defines the axis 19 of the electron beam.
  • the cathode C1 When equal voltages are applied to the metal parts 15 and 16, the cathode C1 emits an electron beam F along the axis 19, the concentration of which is obtained by the geometry of the cathode C1.
  • the X-ray tube which has just been described exhibits satisfactory deflection performance without requiring the application of excessively high voltages.
  • the beam concentration is not satisfactory for applications in which it is necessary for the X-ray source to be punctual and for the energy distribution of the X-ray beam to be uniformly and symmetrically distributed over its section.
  • the invention provides an X-ray tube in which the functions of concentration and deflection are spatially separated at the level of the cathode.
  • the invention relates to an X-ray tube comprising in a vacuum enclosure a cathode which emits an electron beam and an anode which receives said beam and emits X-radiation, said cathode being made of an emitting filament.
  • electrons and an electron beam concentrating device characterized in that it further comprises two deflection electrodes arranged on either side of the electron beam and isolated from the cathode and the anode, said electrodes being able to be brought to potentials different from each other and from those of the cathode.
  • Figure 2 schematically shows an X-ray tube according to the present invention. It comprises, in a vacuum enclosure, represented by the dashed frame 21, a filament 22, a concentration device 23 and an anode 24.
  • the concentration device 23 and the filament 22 constitute a cathode C2.
  • the concentration device 23 consists of a single metal piece which is symmetrical with respect to a plane of symmetry perpendicular to the plane of Figure 2 and containing the axis 25 of the filament 22 perpendicular to the plane of the figure. The intersection of this plane of symmetry with the plane of Figure 2 defines the axis 29 of the electron beam.
  • the opposite and symmetrical faces 26 and 27 of the concentration device 23 are in the form of stair treads, the first step of which is at the filament level 22.
  • a zero or positive voltage is applied to the metal part 23, by means not shown in FIG. 2, a concentration of the electron beam is obtained at a point 28 of the anode 24 located on the axis 29.
  • the deflection of the electron beam is obtained by metal plates 30 and 31 which extend the steps of the concentration device 23 and are arranged symmetrically with respect to the plane of symmetry. They are electrically isolated from the concentration device by insulating layers 32 and 33. These plates can be brought, by means not shown in FIG. 2, to different potentials with respect to each other, with respect to the metal part 23 and relative to the anode 24.
  • the amplitude of the deflection is not proportional to the length of the plates as one might think a priori.
  • FIGS. 4a and 4b are diagrams showing the density A of the energy distribution of the impact on the anode as a function of the distance ⁇ of the impact with respect to the axis 29.
  • the diagram in FIG. 4a corresponds to an absence of polarization on the plates while FIG. 4b corresponds to a deflection obtained by applying polarization voltages of + 2000 volts and - 2000 volts. These diagrams show that there is a slight deterioration in the energy distribution of the impact for the part furthest from the axis.
  • FIG. 5b shows that the energy distribution of the beam is less regular over the diameter of the impact when the voltage applied to a plate is 500 volts, the other plate being grounded.
  • the concentration of the beam is obtained using a cathode comprising two steps on either side of the filament. Furthermore, the deflection is obtained by two plates arranged in the external extension of the second step. Such an arrangement leads to applying relatively high deflection voltages on these plates because the energy of the beam is already high at the level of the plates. To reduce these deflection voltages, it is possible ( Figure 6) to remove the last two steps of the cathode and replace them with deflection plates which then act on a beam having less energy. Such an embodiment results in poorer beam concentration since the effect of the concentrating device is less.
  • deflection plates of different lengths and symmetrically polarized or not.
  • the deflection plates may have a profile in the form of stairs.
  • FIGS. 7 and 8 show, by way of non-limiting illustration, two ways among others of producing a cathode with deflection plates according to the present invention. In these figures, elements similar to those of Figure 2 have the same references.
  • the cathode consists of a metal part 40 pierced with at least one hole 41 in its center for the passage of the conductors 42 for feeding the filament 22; these conductors 42 also serve as mechanical support for the filament 22.
  • These conductors 42 are isolated from each other and from the metal part 40 by an insulator 43.
  • the metal part 40 is shaped, filament side, so as to present stair steps referenced 44, 45 on one side and 46, 47 on the other, which separate the edges of the filament piece.
  • the filament is placed at the first step 44 and 46.
  • Each second step 45 or 47 is extended diametrically outward along a flat face 48 or 49 which serves as a support for an insulating bar 50 or 51.
  • This insulating bar 50 or 51 constitutes in a way a third step for the concentration device .
  • Each insulating bar 50 or 51 serves as a support for a metal electrode 52 or 53 which has the shape of a square, one side 54 or 55 of which is fixed to the corresponding bar and the other side of which 56 or 57 comes back parallel to the central axis of the beam.
  • This second side 56 or 57 extends in the direction of the metal part 40 but stops at a certain distance from the latter to avoid any electrical breakdown between the two metal elements brought to different potentials.
  • the deflection voltages are applied to these electrodes 52 and 53 by respective conductors 58 and 59 which each pass through the associated insulating bar 50 or 51 and the metal part 40 by means of holes, in particular the holes 60 and 61 drilled in the metal part. 40.
  • an insulator 62 is provided between the conductor 58 or 59 and the metal part 40.
  • the bias voltage of the cathode is applied via a metal terminal 63.
  • the insulating bars 50 and 51 can be made of any insulating material capable of withstanding high temperatures. This is the case with alumina. These alumina bars can be welded to the metal part 40.
  • metal deflection electrodes 52 and 53 metals or metal alloys which are resistant to high temperatures are also required. Molybdenum can be used which can be welded to the alumina from the insulating bars 50 and 51.
  • FIG. 8 The embodiment of Figure 8 is similar to that of Figure 7 with regard to the cathode and its filament. It differs from it in the way in which the deflection electrodes are produced. While in FIG. 7, the electrodes 52 and 53 are supported by the flat front face 48 or 49 of the cathode on which the insulating bars are fixed, in FIG. 8, the insulating elements 77 and 78 are fixed on the lateral face 79 and 79 ′ outside of the metal part 40.
  • the insulating elements 77 and 78 comprise two distinct parts, one 64 or 65 for fixing to the external lateral face 79 and the another 66 or 67 for supporting the deflection electrodes 68 and 69.
  • the insulating parts 66 and 67 are shaped so as to present, on the filament side, two opposite faces 70 and 71 parallel to the steps of the concentration device.
  • the metal electrodes 68 and 69 are deposited on these opposite faces 70 and 71 as well as on the upper surfaces 72 and 73 and lower 74 and 75 of the insulating parts 66 and 67. These electrodes are connected to a voltage supply device (not shown) by conductors 76 and 76 ′ which pass through the insulating elements 64 and 65.
  • the insulating elements 77 and 78 can be made of any insulating material capable of withstanding high temperatures, for example alumina. These elements 77 and 78 can be welded or glued to the part 40.
  • the material of the electrodes 68 and 69 is a metal or a metal alloy which resists high temperatures, for example molybdenum.

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  • X-Ray Techniques (AREA)

Abstract

The invention relates to X-ray tubes of the beam deflection type. <??>According to the invention the steps of the device 23 for concentrating the electron beam are prolonged by metal deflecting electrodes 30,31 arranged parallel to the said steps and electrically insulated by insulation 32,33 of the latter. These electrodes 30,31 are brought to different potentials whose polarities and values depend on the direction and on the amplitude of the deflection to be obtained. <??>The invention is applicable to instruments for radiology. <IMAGE>

Description

L'invention concerne un tube à rayons X qui est utilisé notamment en radiologie pour obtenir un faisceau de rayons X pouvant avoir différentes directions dans l'espace.The invention relates to an X-ray tube which is used in particular in radiology to obtain an X-ray beam which can have different directions in space.

Ce type de tubes à rayons X est, par exemple mis en oeuvre en radiodiagnostic pour balayer une zone à analyser ou pour obtenir au moins deux faisceaux de rayons X ayant des caractéristiques énergétiques différentes et/ou des angles d'incidence différents sur la zone à analyser.This type of X-ray tube is, for example used in radiodiagnostics to scan an area to be analyzed or to obtain at least two X-ray beams having different energy characteristics and / or different angles of incidence on the area to be analyze.

Un tube à rayons X comporte, dans une enceinte sous vide, une cathode constituée d'un filament chauffé qui émet des électrons et d'un dispositif de concentration adossé au filament qui focalise les électrons émis sur une anode portée à un potentiel positif par rapport à la cathode. Le point d'impact du faisceau d'électrons sur l'anode constitue la source de rayonnement X sous la forme d'un faisceau.An X-ray tube comprises, in a vacuum enclosure, a cathode made up of a heated filament which emits electrons and of a concentration device backed by the filament which focuses the electrons emitted on an anode brought to a positive potential compared to at the cathode. The point of impact of the electron beam on the anode constitutes the source of X-radiation in the form of a beam.

Pour déplacer angulairement le faisceau de rayons X, il est généralement proposé de déplacer le point d'impact du faisceau d'électrons sur l'anode à l'aide de moyens de déflexion. Ces moyens de déflexion sont habituellement constitués par des lentilles magnétiques ou électrostatiques qui sont disposées sur le trajet du faisceau ou à proximité de ce trajet entre la cathode et l'anode. La mise en oeuvre de ces lentilles nécessite une énergie non négligeable du fait de l'importante énergie cinétique des électrons du faisceau due à leur grande vitesse par suite d'une différence de potentiels élevée entre la cathode et l'anode, supérieure à cent kilovolts.To angularly move the X-ray beam, it is generally proposed to move the point of impact of the electron beam on the anode using deflection means. These deflection means are usually constituted by magnetic or electrostatic lenses which are arranged on the path of the beam or near this path between the cathode and the anode. The implementation of these lenses requires a significant energy due to the high kinetic energy of the beam electrons due to their high speed due to a high potential difference between the cathode and the anode, greater than one hundred kilovolts.

Dans le brevet français 2 538 948, il a été proposé un tube à rayons X à balayage dans lequel le dispositif de concentration comporte au moins deux pièces métalliques qui sont électriquement isolées l'une de l'autre et du filament pour permettre leur polarisation indépendante par rapport à ce dernier et ainsi obtenir une déflexion du faisceau d'électrons.In French patent 2,538,948, a scanning X-ray tube has been proposed in which the concentration device comprises at least two metal parts which are electrically isolated from each other and from the filament to allow their independent polarization. relative to the latter and thus obtain a deflection of the electron beam.

La figure 1 montre schématiquement un tube à rayons X du type de celui decrit dans la demande de brevet précitée. Il comprend, dans une enceinte sous vide représentée par le rectangle 11 en tirets, un filament 12, un dispositif de concentration 13 adossé au filament 12 et une anode 14. Le filament 12 et le dispositif de concentration 13 constituent une cathode C1. Le dispositif de concentration 13 est constitué d'une première pièce métallique 15 et d'une seconde pièce métallique 16 qui sont électriquement isolées l'une de l'autre par une cloison isolante 17 solidaire d'une embase isolante 18. Les pièces métalliques 15 et 16 sont disposées symétriquement de part et d'autre du filament 12 par rapport à un plan de symétrie perpendiculaire au plan de la figure 1. Ce plan de symétrie contient l'axe du filament 12 perpendiculaire au plan de la figure 1 et est perpendiculaire à l'embase 18. L'intersection de ce plan de symétrie avec le plan de la figure 1 définit l'axe 19 du faisceau d'électrons.Figure 1 schematically shows an X-ray tube of the type described in the aforementioned patent application. It comprises, in a vacuum enclosure represented by the dashed rectangle 11, a filament 12, a concentration device 13 attached to the filament 12 and an anode 14. The filament 12 and the concentration device 13 constitute a cathode C1. The concentration device 13 consists of a first metal part 15 and a second metal part 16 which are electrically insulated from each other by an insulating partition 17 secured to an insulating base 18. The metal parts 15 and 16 are arranged symmetrically on either side of the filament 12 with respect to a plane of symmetry perpendicular to the plane of Figure 1. This plane of symmetry contains the axis of the filament 12 perpendicular to the plane of Figure 1 and is perpendicular at the base 18. The intersection of this plane of symmetry with the plane of Figure 1 defines the axis 19 of the electron beam.

Lorsque des tensions égales sont appliquées aux pièces métalliques 15 et 16, la cathode C1 émet un faisceau d'électrons F suivant l'axe 19 dont la concentration est obtenue par la géométrie de la cathode C1.When equal voltages are applied to the metal parts 15 and 16, the cathode C1 emits an electron beam F along the axis 19, the concentration of which is obtained by the geometry of the cathode C1.

Pour obtenir une déflexion du faisceau d'électrons, c'est-à-dire conférer à ce dernier une direction moyenne différente de l'axe d'émission 19, il suffit d'introduire une dissymétrie au champ électrique créé autour du filament 12 en donnant des valeurs différentes aux tensions appliquées aux pièces métalliques 15 et 16, l'une de ces valeurs pouvant être nulle mais aucune ne devant être positive. Ainsi on obtient un faisceau F′ d'axe 19′ pour une différence de potentiels positive entre la pièce 15 et la pièce 16; par contre, on obtient un faisceau F˝ d'axe 19˝ pour une différence de potentiels négative entre la pièce 15 et la pièce 16.To obtain a deflection of the electron beam, that is to say to give the latter an average direction different from the emission axis 19, it suffices to introduce an asymmetry to the electric field created around the filament 12 by giving different values to the voltages applied to the metal parts 15 and 16, one of these values possibly being zero but none having to be positive. Thus a beam F ′ with axis 19 ′ is obtained for a positive potential difference between the part 15 and the part 16; on the other hand, a beam F˝ with an axis 19˝ is obtained for a negative potential difference between the part 15 and the part 16.

Le tube à rayons X qui vient d'être décrit présente des performances de déflexion satisfaisantes sans nécessiter l'application de tensions trop élevées. Cependant, la concentration du faisceau n'est pas satisfaisante pour des applications dans lesquelles il est nécessaire que la source de rayons X soit ponctuelle et que la répartition énergétique du faisceau de rayons X soit uniformément et symétriquement répartie sur sa section.The X-ray tube which has just been described exhibits satisfactory deflection performance without requiring the application of excessively high voltages. However, the beam concentration is not satisfactory for applications in which it is necessary for the X-ray source to be punctual and for the energy distribution of the X-ray beam to be uniformly and symmetrically distributed over its section.

Pour pallier ces inconvénients, l'invention propose un tube à rayons X dans lequel les fonctions de concentration et de déflexion sont séparées spatialement au niveau de la cathode.To overcome these drawbacks, the invention provides an X-ray tube in which the functions of concentration and deflection are spatially separated at the level of the cathode.

L'invention se rapporte à un tube à rayons X comportant dans une enceinte sous vide une cathode qui émet un faisceau d'électrons et une anode qui reçoit ledit faisceau et émet un rayonnement X, ladite cathode étant constituée d'un filament émetteur d'électrons et d'un dispositif de concentration du faisceau d'électrons, caractérisé en ce qu'il comporte en outre deux électrodes de déflexion disposées de part et d'autre du faisceau d'électrons et isolées de la cathode et de l'anode, lesdites électrodes pouvant être portées à des potentiels différents entre eux et de ceux de la cathode.The invention relates to an X-ray tube comprising in a vacuum enclosure a cathode which emits an electron beam and an anode which receives said beam and emits X-radiation, said cathode being made of an emitting filament. electrons and an electron beam concentrating device, characterized in that it further comprises two deflection electrodes arranged on either side of the electron beam and isolated from the cathode and the anode, said electrodes being able to be brought to potentials different from each other and from those of the cathode.

Selon l'invention, les électrodes de déflexion sont fixées chacune à la cathode par l'intermédiaire d'un élément isolant et sont constituées par des plaques métalliques opposées l'une à l'autre et parallèles à l'axe du faisceau d'électrons en l'absence de déflexion. D'autres caractéristiques et avantages de la présente invention apparaîtront à la lecture de la description suivante d'exemples particuliers de réalisation, ladite description étant faite en relation avec les dessins joints dans lesquels :

  • - la figure 1 est un schéma d'un tube à rayons X selon l'art antérieur,
  • - la figure 2 est un schéma d'un tube à rayons X selon l'invention,
  • - la figure 3 est un diagramme permettant de déterminer la longueur optimale des électrodes de déflexion,
  • - les figures 4a et 4b sont des diagrammes montrant la déflexion du faisceau et sa répartition énergétique pour des polarisations symétriques des électrodes de déflexion par rapport au potentiel de la masse,
  • - les figures 5a et 5b sont des diagrammes montrant la déflexion du faisceau et sa répartition énergétique en l'absence de polarisation (fig. 5a) des électrodes de déflexion ou pour une polarisation dissymétrique (fig. 5b).
  • - la figure 6 est un schéma d'une variante d'un tube à rayons X selon l'invention, et
  • - les figures 7 et 8 illustrent en coupe axiale des modes de réalisation de cathodes de tubes à rayons X selon l'invention.
According to the invention, the deflection electrodes are each fixed to the cathode by means of an insulating element and are constituted by metal plates opposite to each other and parallel to the axis of the electron beam in the absence of deflection. Other characteristics and advantages of the present invention will appear on reading the following description of particular embodiments, said description being made in relation to the accompanying drawings in which:
  • FIG. 1 is a diagram of an X-ray tube according to the prior art,
  • FIG. 2 is a diagram of an X-ray tube according to the invention,
  • FIG. 3 is a diagram making it possible to determine the optimal length of the deflection electrodes,
  • FIGS. 4a and 4b are diagrams showing the deflection of the beam and its energy distribution for symmetrical polarizations of the deflection electrodes with respect to the ground potential,
  • - Figures 5a and 5b are diagrams showing the deflection of the beam and its energy distribution in the absence of polarization (fig. 5a) of the deflection electrodes or for asymmetric polarization (fig. 5b).
  • FIG. 6 is a diagram of a variant of an X-ray tube according to the invention, and
  • - Figures 7 and 8 illustrate in axial section embodiments of cathodes of X-ray tubes according to the invention.

La figure 2 montre schématiquement un tube à rayons X selon la présente invention. Il comprend, dans une enceinte sous vide, représentée par le cadre en tirets 21, un filament 22, un dispositif de concentration 23 et une anode 24. Le dispositif de concentration 23 et le filament 22 constituent une cathode C2. Le dispositif de concentration 23 est constitué d'une seule pièce métallique qui est symétrique par rapport à un plan de symétrie perpendiculaire au plan de la figure 2 et contenant l'axe 25 du filament 22 perpendiculaire au plan de la figure. L'intersection de ce plan de symétrie avec le plan de la figure 2 définit l'axe 29 du faisceau d'électrons.Figure 2 schematically shows an X-ray tube according to the present invention. It comprises, in a vacuum enclosure, represented by the dashed frame 21, a filament 22, a concentration device 23 and an anode 24. The concentration device 23 and the filament 22 constitute a cathode C2. The concentration device 23 consists of a single metal piece which is symmetrical with respect to a plane of symmetry perpendicular to the plane of Figure 2 and containing the axis 25 of the filament 22 perpendicular to the plane of the figure. The intersection of this plane of symmetry with the plane of Figure 2 defines the axis 29 of the electron beam.

De manière connue, les faces opposées et symétriques 26 et 27 du dispositif de concentration 23 sont en forme de marches d'escalier dont la première marche est au niveau filament 22. Lorsqu'une tension nulle ou positive est appliquée à la pièce métallique 23, par des moyens non représentés sur la figure 2, on obtient une concentration du faisceau d'électrons en un point 28 de l'anode 24 situé sur l'axe 29.In known manner, the opposite and symmetrical faces 26 and 27 of the concentration device 23 are in the form of stair treads, the first step of which is at the filament level 22. When a zero or positive voltage is applied to the metal part 23, by means not shown in FIG. 2, a concentration of the electron beam is obtained at a point 28 of the anode 24 located on the axis 29.

Selon l'invention, la déflexion du faisceau d'électrons est obtenue par des plaques métalliques 30 et 31 qui prolongent les marches du dispositif de concentration 23 et sont disposées symétriquement par rapport au plan de symétrie. Elles sont électriquement isolées du dispositif de concentration par des couches isolantes 32 et 33. Ces plaques peuvent être portées, par des moyens non représentés sur la figure 2, à des potentiels différents l'un par rapport à l'autre, par rapport à la pièce métallique 23 et par rapport à l'anode 24.According to the invention, the deflection of the electron beam is obtained by metal plates 30 and 31 which extend the steps of the concentration device 23 and are arranged symmetrically with respect to the plane of symmetry. They are electrically isolated from the concentration device by insulating layers 32 and 33. These plates can be brought, by means not shown in FIG. 2, to different potentials with respect to each other, with respect to the metal part 23 and relative to the anode 24.

Ainsi, en appliquant une tension de + 2000 volts sur la plaque supérieure 30 et une tension de - 2000 volts sur la plaque inférieure 31, on obtient une déflexion du faisceau vers la plaque supérieure 30. Bien entendu, la déflexion serait inverse, c'est-à-dire vers la plaque inférieure, au cas où les tensions seraient inversées sur les plaques. L'amplitude de la déflexion sur l'anode est d'un millimètre environ lorsque la distance cathode-anode est de deux centimètres environ. Par ailleurs, la longueur des plaques 30 et 31 dans le sens de la propagation est de trois millimètres environ.Thus, by applying a voltage of + 2000 volts on the upper plate 30 and a voltage of - 2000 volts on the lower plate 31, one obtains a deflection of the beam towards the upper plate 30. Of course, the deflection would be inverse, this that is to say towards the lower plate, in case the voltages are reversed on the plates. The amplitude of the deflection on the anode is approximately one millimeter when the distance cathode-anode is about two centimeters. Furthermore, the length of the plates 30 and 31 in the direction of propagation is approximately three millimeters.

Il est à remarquer que l'amplitude de la déflexion n'est pas proportionnelle à la longueur des plaques comme on pourrait le penser a priori.It should be noted that the amplitude of the deflection is not proportional to the length of the plates as one might think a priori.

C'est ce que montre le diagramme des courbes H1, H2, H3 de la figure 3 dans lequel on a représenté la déflexion δ sur l'anode en fonction de la tension Vp en valeur absolue appliquée sur les plaques 30 et 31 pour différentes longueurs respectives h1, h2 et h3 desdites plaques telles que h1 < h2 < h3 , la tension cathode-anode restant égale à 140 kilovolts environ.This is shown by the diagram of the curves H1, H2, H3 in FIG. 3 in which the deflection δ on the anode has been represented as a function of the voltage V p in absolute value applied to the plates 30 and 31 for different respective lengths h1, h2 and h3 of said plates such that h1 <h2 <h3, the cathode-anode voltage remaining equal to approximately 140 kilovolts.

Dans ce diagramme, la déflexion la plus grande a été obtenue avec la longueur h2 qui est intermédiaire entre h1 et h3.In this diagram, the greatest deflection was obtained with the length h2 which is intermediate between h1 and h3.

Les courbes de la figure 3 montrent également que la déflexion sur l'anode est directement proportionnelle aux tensions appliquées aux plaques.The curves in FIG. 3 also show that the deflection on the anode is directly proportional to the voltages applied to the plates.

Les figures 4a et 4b sont des diagrammes montrant la densité A de la répartition énergétique de l'impact sur l'anode en fonction de la distance δ de l'impact par rapport à l'axe 29. Le diagramme de la figure 4a correspond à une absence de polarisation sur les plaques tandis que la figure 4b correspond à une déflexion obtenue en appliquant des tensions de polarisation de + 2000 volts et - 2000 volts. Ces diagrammes montrent qu'il y a une légère détérioration de la répartition énergétique de l'impact pour la partie la plus éloignée de l'axe.FIGS. 4a and 4b are diagrams showing the density A of the energy distribution of the impact on the anode as a function of the distance δ of the impact with respect to the axis 29. The diagram in FIG. 4a corresponds to an absence of polarization on the plates while FIG. 4b corresponds to a deflection obtained by applying polarization voltages of + 2000 volts and - 2000 volts. These diagrams show that there is a slight deterioration in the energy distribution of the impact for the part furthest from the axis.

Au lieu d'appliquer des tensions inverses sur les plaques, il est possible de leur appliquer des tensions dissymétriques, par exemple - 500 volts sur l'une et le potentiel de la masse sur l'autre. On obtient, bien entendu, des déflexions moins importantes mais avec une détérioration de la répartition énergétique du point d'impact sur l'anode. C'est ce que montrent les diagrammes des figures 5a et 5b analogues à ceux des figures 4a et 4b mais avec une tension appliquée à la cathode égale à la moitié de celle utilisée dans le cas de la figure 4.Instead of applying reverse voltages to the plates, it is possible to apply asymmetrical voltages to them, for example - 500 volts on one and the ground potential on the other. We get, well understood, less significant deflections but with a deterioration of the energy distribution of the point of impact on the anode. This is shown by the diagrams in FIGS. 5a and 5b similar to those in FIGS. 4a and 4b but with a voltage applied to the cathode equal to half of that used in the case of FIG. 4.

La figure 5b montre que la répartition énergétique du faisceau est moins régulière sur le diamètre de l'impact lorsque la tension appliquée sur une plaque est de 500 volts, l'autre plaque étant à la masse.FIG. 5b shows that the energy distribution of the beam is less regular over the diameter of the impact when the voltage applied to a plate is 500 volts, the other plate being grounded.

Sur l'exemple schématique de réalisation de la figure 2 la concentration du faisceau est obtenue à l'aide d'une cathode comportant deux marches de part et d'autre du filament. Par ailleurs, la déflexion est obtenue par deux plaques disposées dans le prolongement extérieur de la deuxième marche. Une telle disposition conduit à appliquer des tensions de déflexion relativement élevées sur ces plaques car l'énergie du faisceau est déjà importante au niveau des plaques. Pour diminuer ces tensions de déflexion, il est possible (figure 6) de supprimer les deux dernières marches de la cathode et de les remplacer par des plaques de déflexion qui agissent alors sur un faisceau présentant moins d'énergie. Une telle réalisation conduit à une moins bonne concentration du faisceau car l'effet du dispositif de concentration est moindre.In the schematic embodiment of FIG. 2, the concentration of the beam is obtained using a cathode comprising two steps on either side of the filament. Furthermore, the deflection is obtained by two plates arranged in the external extension of the second step. Such an arrangement leads to applying relatively high deflection voltages on these plates because the energy of the beam is already high at the level of the plates. To reduce these deflection voltages, it is possible (Figure 6) to remove the last two steps of the cathode and replace them with deflection plates which then act on a beam having less energy. Such an embodiment results in poorer beam concentration since the effect of the concentrating device is less.

Afin d'aboutir au résultat recherché, de multiples variantes peuvent être envisagées telles que celles décrites ci-dessus. On peut en ajouter d'autres sans sortir du cadre de la présente invention telles que des plaques de déflexion de longueurs différentes et polarisées symétriquement ou non. Egalement, les plaques de déflexion peuvent présenter un profil en forme de marches d'escalier.In order to achieve the desired result, multiple variants can be envisaged such as those described above. We can add others without departing from the scope of the present invention such as deflection plates of different lengths and symmetrically polarized or not. Also, the deflection plates may have a profile in the form of stairs.

Un tube à rayons X selon l'invention a été décrit à l'aide de vues schématiques sans indiquer la manière de réaliser de telles plaques de déflexion solidaires de la cathode. Les figures 7 et 8 montrent, à titre illustratif et non limitatif, deux façons parmi d'autres de réaliser une cathode à plaques de déflexion selon la présente invention. Dans ces figures, les éléments analogues à ceux de la figure 2 portent les mêmes références.An X-ray tube according to the invention has been described using schematic views without indicating the manner of producing such deflection plates integral with the cathode. FIGS. 7 and 8 show, by way of non-limiting illustration, two ways among others of producing a cathode with deflection plates according to the present invention. In these figures, elements similar to those of Figure 2 have the same references.

Dans le mode de réalisation de la figure 7, la cathode est constituée d'une pièce métallique 40 percée d'au moins un trou 41 en son centre pour le passage des conducteurs 42 d'alimentation du filament 22; ces conducteurs 42 servent également de support mécanique au filament 22. Ces conducteurs 42 sont isolés entre eux et vis-à-vis de la pièce métallique 40 par un isolant 43.In the embodiment of FIG. 7, the cathode consists of a metal part 40 pierced with at least one hole 41 in its center for the passage of the conductors 42 for feeding the filament 22; these conductors 42 also serve as mechanical support for the filament 22. These conductors 42 are isolated from each other and from the metal part 40 by an insulator 43.

Pour obtenir la concentration souhaitée du faisceau d'électrons, la pièce métallique 40 est conformée, côté filament, de manière à présenter des marches d'escalier référencées 44, 45 d'un côté et 46, 47 de l'autre, qui éloignent les bords de la pièce du filament. Le filament est disposé au niveau de la première marche 44 et 46.To obtain the desired concentration of the electron beam, the metal part 40 is shaped, filament side, so as to present stair steps referenced 44, 45 on one side and 46, 47 on the other, which separate the edges of the filament piece. The filament is placed at the first step 44 and 46.

Chaque deuxième marche 45 ou 47 se prolonge diamétralement vers l'extérieur suivant une face plane 48 ou 49 qui sert de support à une barre isolante 50 ou 51. Cette barre isolante 50 ou 51 constitue en quelque sorte une troisième marche pour le dispositif de concentration. Chaque barre isolante 50 ou 51 sert de support à une électrode métallique 52 ou 53 qui a la forme d'une équerre dont un côté 54 ou 55 est fixé sur la barre correspondante et dont l'autre côté 56 ou 57 vient en retour parallèlement à l'axe central du faisceau. Ce deuxième côté 56 ou 57 s'étend en direction de la pièce métallique 40 mais s'arrête à une certaine distance de cette dernière pour éviter tout claquage électrique entre les deux éléments métalliques portés à des potentiels différents.Each second step 45 or 47 is extended diametrically outward along a flat face 48 or 49 which serves as a support for an insulating bar 50 or 51. This insulating bar 50 or 51 constitutes in a way a third step for the concentration device . Each insulating bar 50 or 51 serves as a support for a metal electrode 52 or 53 which has the shape of a square, one side 54 or 55 of which is fixed to the corresponding bar and the other side of which 56 or 57 comes back parallel to the central axis of the beam. This second side 56 or 57 extends in the direction of the metal part 40 but stops at a certain distance from the latter to avoid any electrical breakdown between the two metal elements brought to different potentials.

Ces électrodes métalliques 52 et 53, et notamment leur partie 56 ou 57, constituent les plaques de déflexion décrites précédemment. Les tensions de déflexion sont appliquées à ces électrodes 52 et 53 par des conducteurs respectifs 58 et 59 qui traversent chacun la barre isolante associée 50 ou 51 et la pièce métallique 40 grâce à des trous, notamment les trous 60 et 61 percés dans la pièce métallique 40. Bien entendu, il est prévu un isolant 62 entre le conducteur 58 ou 59 et la pièce métallique 40.These metal electrodes 52 and 53, and in particular their part 56 or 57, constitute the deflection plates described above. The deflection voltages are applied to these electrodes 52 and 53 by respective conductors 58 and 59 which each pass through the associated insulating bar 50 or 51 and the metal part 40 by means of holes, in particular the holes 60 and 61 drilled in the metal part. 40. Of course, an insulator 62 is provided between the conductor 58 or 59 and the metal part 40.

Par ailleurs, la tension de polarisation de la cathode est appliquée par l'intermédiaire d'une borne métallique 63.Furthermore, the bias voltage of the cathode is applied via a metal terminal 63.

Les barres isolantes 50 et 51 peuvent être réalisées en tout matériau isolant susceptible de supporter des températures élevées. Il en est ainsi de l'alumine. Ces barres en alumine peuvent être soudées sur la pièce métallique 40.The insulating bars 50 and 51 can be made of any insulating material capable of withstanding high temperatures. This is the case with alumina. These alumina bars can be welded to the metal part 40.

En ce qui concerne les électrodes métalliques de déflexion 52 et 53, il faut également des métaux ou des alliages de métaux qui résistent aux hautes températures. On peut utiliser du molybdène qui peut être soudé à l'alumine des barres isolantes 50 et 51.With regard to the metal deflection electrodes 52 and 53, metals or metal alloys which are resistant to high temperatures are also required. Molybdenum can be used which can be welded to the alumina from the insulating bars 50 and 51.

Le mode de réalisation de la figure 8 est semblable à celui de la figure 7 en ce qui concerne la cathode et son filament. Il en diffère par la manière dont sont réalisées les électrodes de déflexion. Alors que sur la figure 7, les électrodes 52 et 53 sont supportées par la face avant plane 48 ou 49 de la cathode sur laquelle les barres isolantes sont fixées, sur la figure 8, les éléments isolants 77 et 78 sont fixés sur la face latérale 79 et 79′ extérieure de la pièce métallique 40. Les éléments isolants 77 et 78 comprennent deux parties distinctes, l'une 64 ou 65 de fixation à la face latérale extérieure 79 et l'autre 66 ou 67 de support des électrodes de déflexion 68 et 69. Les parties isolantes 66 et 67 sont conformées de manière à présenter, côté filament, deux faces opposées 70 et 71 parallèles aux marches du dispositif de concentration. Les électrodes métalliques 68 et 69 sont déposées sur ces faces opposées 70 et 71 ainsi que sur les surfaces supérieures 72 et 73 et inférieures 74 et 75 des parties isolantes 66 et 67. Ces électrodes sont connectées à un dispositif d'alimentation en tension (non représenté) par des conducteurs 76 et 76′ qui traversent les éléments isolants 64 et 65.The embodiment of Figure 8 is similar to that of Figure 7 with regard to the cathode and its filament. It differs from it in the way in which the deflection electrodes are produced. While in FIG. 7, the electrodes 52 and 53 are supported by the flat front face 48 or 49 of the cathode on which the insulating bars are fixed, in FIG. 8, the insulating elements 77 and 78 are fixed on the lateral face 79 and 79 ′ outside of the metal part 40. The insulating elements 77 and 78 comprise two distinct parts, one 64 or 65 for fixing to the external lateral face 79 and the another 66 or 67 for supporting the deflection electrodes 68 and 69. The insulating parts 66 and 67 are shaped so as to present, on the filament side, two opposite faces 70 and 71 parallel to the steps of the concentration device. The metal electrodes 68 and 69 are deposited on these opposite faces 70 and 71 as well as on the upper surfaces 72 and 73 and lower 74 and 75 of the insulating parts 66 and 67. These electrodes are connected to a voltage supply device (not shown) by conductors 76 and 76 ′ which pass through the insulating elements 64 and 65.

On remarquera que les faces inférieures 73 et 74 sont écartées de la pièce métallique 40 de manière à éviter un claquage électrique.It will be noted that the lower faces 73 and 74 are separated from the metal part 40 so as to avoid electrical breakdown.

Les éléments isolants 77 et 78 peuvent être réalisés en tout matériau isolant susceptible de supporter des températures élevées, par exemple en alumine. Ces éléments 77 et 78 peuvent être soudés ou collés à la pièce 40. Le matériau des électrodes 68 et 69 est un métal ou un alliage de métaux qui résiste aux hautes températures, par exemple le molybdène.The insulating elements 77 and 78 can be made of any insulating material capable of withstanding high temperatures, for example alumina. These elements 77 and 78 can be welded or glued to the part 40. The material of the electrodes 68 and 69 is a metal or a metal alloy which resists high temperatures, for example molybdenum.

Claims (5)

1. Tube à rayons X comportant, dans une enceinte sous vide, une cathode (C2) qui émet un faisceau d'électrons et une anode (24) qui reçoit ledit faisceau et émet un rayonnement X, ladite cathode (C2) étant constituée d'un filament (22) émetteur d'électrons, d'un dispositif de concentration (23) du faisceau d'électrons et de deux électrodes de déflexion (30,31) disposées de part et d'autre du faisceau d'électrons et isolées de la cathode (C2) et de l'anode (24), lesdites électrodes pouvant être portées à des potentiels différents entre eux et de celui de la cathode et de l'anode,
caractérisé en ce que lesdites électrodes de déflexion (30,31) sont disposées à proximité immédiate dudit dispositif de concentration (23) et dans le prolongement de ce dernier et sont fixées chacune à la cathode (C2) par l'intermédiaire d'un élément isolant (32,33 ou 50,51 ou 66,67).1. X-ray tube comprising, in a vacuum enclosure, a cathode (C2) which emits an electron beam and an anode (24) which receives said beam and emits X-radiation, said cathode (C2) consisting of '' an electron emitting filament (22), a device (23) for concentrating the electron beam and two deflection electrodes (30, 31) arranged on either side of the electron beam and isolated the cathode (C2) and the anode (24), the said electrodes being able to be brought to potentials different from each other and from that of the cathode and the anode,
characterized in that said deflection electrodes (30,31) are arranged in the immediate vicinity of and in the extension of said concentration device (23) and are each fixed to the cathode (C2) by means of an element insulator (32.33 or 50.51 or 66.67). 2. Tube à rayons X selon la revendication 1, caractérisé en ce que lesdites électrodes de déflexion (30,31) sont constituées par des plaques métalliques opposées l'une à l'autre et parallèles à l'axe (29) du faisceau d'électrons en l'absence de déflexion.2. X-ray tube according to claim 1, characterized in that said deflection electrodes (30,31) are constituted by metal plates opposite one another and parallel to the axis (29) of the beam d electrons in the absence of deflection. 3. Tube à rayons X selon la revendication 2, caractérisé en ce que les plaques métalliques (30,31) sont obtenues par dépôt d'un métal ou d'un alliage métallique sur les éléments isolants (66,67), lesdits éléments isolants étant conformés pour présenter entre eux deux faces en regard parallèles à l'axe du faisceau d'électrons en l'absence de déflexion.3. X-ray tube according to claim 2, characterized in that the metal plates (30,31) are obtained by depositing a metal or a metal alloy on the insulating elements (66,67), said insulating elements being shaped to present between them two opposite faces parallel to the axis of the electron beam in the absence of deflection. 4. Tube à rayons X selon la revendication 2 ou 3 caractérisé en ce que l'élément isolant (32,33 ou 50,51 ou 66,67) est de l'alumine.4. X-ray tube according to claim 2 or 3 characterized in that the insulating element (32.33 or 50.51 or 66.67) is alumina. 5. Tube à rayons X selon l'une quelconque des revendications précédentes, caractérisé en ce que les potentiels appliqués sur les deux électrodes sont égaux mais de polarités opposées.5. X-ray tube according to any one of the preceding claims, characterized in that the potentials applied to the two electrodes are equal but of opposite polarities.
EP90400622A 1989-03-24 1990-03-08 Beam switching X-ray tube with deflection plates Withdrawn EP0389326A1 (en)

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FR8903888A FR2644931A1 (en) 1989-03-24 1989-03-24 SCANNING X-RAY TUBE WITH DEFLECTION PLATES
FR8903888 1989-03-24

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