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EP2556525B1 - Microfocus x-ray tube with cathode element and process using the same - Google Patents

Microfocus x-ray tube with cathode element and process using the same Download PDF

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Publication number
EP2556525B1
EP2556525B1 EP10716475.8A EP10716475A EP2556525B1 EP 2556525 B1 EP2556525 B1 EP 2556525B1 EP 10716475 A EP10716475 A EP 10716475A EP 2556525 B1 EP2556525 B1 EP 2556525B1
Authority
EP
European Patent Office
Prior art keywords
microfocus
ray tube
filament
electron beam
cathode element
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.)
Active
Application number
EP10716475.8A
Other languages
German (de)
French (fr)
Other versions
EP2556525A1 (en
Inventor
Eberhard Neuser
Andreas Schmitt
Wolfgang Sperner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Baker Hughes Digital Solutions GmbH
Original Assignee
GE Sensing and Inspection Technologies GmbH
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Publication of EP2556525A1 publication Critical patent/EP2556525A1/en
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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/15—Cathodes heated directly by an electric current
    • H01J1/16—Cathodes heated directly by an electric current characterised by the shape
    • 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 invention relates to a microfocus X-ray tube with a cathode element comprising a heatable filament formed from a wire for the glow emission of electrons to form an electron beam.
  • a cathode element comprising a heatable filament formed from a wire for the glow emission of electrons to form an electron beam.
  • hairpin filaments are used to achieve a focal spot size in the micron range, where the wire is bent to a sharp point to emit a fine electron beam.
  • hairpin filaments only have a relatively short life, which is why the cathode must be regularly replaced after a limited number of operating hours.
  • significant additional service costs and corresponding downtime are caused, which in particular preclude the use of microfocus X-ray inspection devices in industrial production.
  • US 2009 129550 A1 disclose different cathode elements for x-ray tubes.
  • US Pat. No. 6,600,809 B1 discloses a microfocus X-ray tube with a hairpin filament.
  • the object of the invention is to provide a microfocus X-ray tube, which can be adapted in a particularly simple way for the user to different applications.
  • the invention solves this problem with the means of the independent claims. Due to the inventive elongated extension of the filament, in the source region of the electron beam, in two directions perpendicular to the electron beam, the effective electron-emissive surface can be significantly increased, so that a considerably lower filament temperature is sufficient to emit the same electron current as compared to the substantially punctiform extent of the electron-emitting tip of a hairpin filament. Elongation of the filament means that the extent is significantly, in particular at least 50% greater than the thickness of the wire, preferably at least twice as large, more preferably at least three times as large. The lower filament temperature leads to a considerable extension of the life of the filament and thus of the cathode element.
  • the invention can be achieved by a multiple, up to an order of magnitude and more, extended filament life. Surprisingly, it has been shown that, despite the increased electron-emitting area, a focal point size of less than 10 ⁇ m, preferably 7 ⁇ m and less, can be achieved. Due to the invention, it is therefore possible to use high-resolution microfocus X-ray inspection devices in industrial production.
  • the filament in the source region of the electron beam on a plurality of juxtaposed wire sections.
  • the wire sections are formed by a plurality of wire loops so that the electron-emitting region of the filament has the shape of a wire helix.
  • the wire portions are spaced from each other. Then the wire edges, ie the lateral Contribute wire surfaces between the wire sections, in addition to the electron-emitting surface, whereby the effect according to the invention can be further increased.
  • the number of wire sections is at least three in order to achieve a significant increase in the electron-emitting area.
  • the number of electron-emitting wire sections is preferably at most ten, more preferably at most six, in order to be able to achieve a microfocus, ie a focal spot of the electron beam of at most 10 ⁇ m.
  • An odd number of wire sections is advantageous because the beam profile of the electron beam becomes more favorable due to the one exactly central wire section. Particularly preferred are three, five or seven wire sections.
  • the cathode element is designed as a replaceable unit for use in an exchange of a microfocus X-ray tube. Consequently, depending on the application, a cathode element according to the invention or a cathode element with a hairpin filament can be inserted into the interchangeable receptacle of a microfocus X-ray tube according to the invention.
  • a microfocus X-ray tube according to the invention comprises a condenser lens in order to align the electron beam approximately parallel in the case of a cathode element according to the invention. This makes it possible, in particular using a downstream conventional focusing lens, to obtain the specified nominal sizes of the tube regardless of the type of cathode element used.
  • the condenser lens becomes in the case of a cathode element with a hairpin filament expediently switched off. An adaptation of the focusing lens to the cathode element according to the invention is not required.
  • the microcomputer tomography system shown comprises an x-ray system 10 which is set up to record a set of x-ray projections of a sample 13.
  • X-ray system 10 comprises a microfocus X-ray tube 11 emitting X-radiation 14 from a focal point or focus 16 of X-ray tube 11, an X-ray imaging detector 12, and a sample holder 20 preferably arranged to rotate sample 13 about a vertical axis.
  • the X-ray detector 12 is preferably an area detector, in particular a flat-panel detector, but a line detector is also possible.
  • a set of X-ray projections of the sample 13 is obtained, for example, by stepwise rotating the sample holder 20 by a defined small angle step and recording an X-ray projection at each rotation angle.
  • the X-ray system 10 is not limited to rotation of the sample holder 20 about a vertical axis.
  • the X-ray tube 11 and the X-ray detector 12 may be rotated around the fixed sample 13.
  • the X-ray projections are read out of the X-ray detector 12 and transmitted to a computer device 41 where reconstructed three-dimensional volume data of the sample 13 are calculated from the recorded set of X-ray projections by means of a basically known reconstruction algorithm and displayed, for example, on a screen 42.
  • the computing device 41 may, as in Fig. 1 also be arranged to control the X-ray source 11, the sample holder 20 and the X-ray detector 12; Alternatively, a separate control device may be provided.
  • the microfocus X-ray tube 11 comprises a cathode element 15, a Wehnelt cylinder 21, an anode 19, a focusing lens 22, preferably embodied as an electromagnetic lens, and an electron beam target 23. Furthermore, a further electromagnetic lens 25 may be provided. which is arranged as a condenser lens to align the electron beam 24 approximately parallel.
  • the microfocus X-ray tube 11 further expediently comprises a deflection unit (not shown) for adjusting the beam position.
  • the cathode element 15 comprises a filament 17, which consists of a suitable wire 27, in particular of tungsten, and is mounted on an insulating, for example made of a ceramic base 34.
  • the filament wire 27 preferably has a thickness in the range of 100 microns to 300 microns, for example, about 200 microns, on.
  • a heating voltage is applied to the glow emission of electrons from the filamentary wire 27.
  • an acceleration voltage generated by a high-voltage generator is applied to accelerate the electrons extracted from the wire toward the anode 19 and to generate an electron beam 24.
  • the maximum acceleration voltage is preferably at least 100 kV, preferably at least 200 kV.
  • the generated electron beam is focused by means of the focusing lens 22 on the target 23, whereby the X-ray radiation 14 is generated.
  • the target 23 is preferably arranged in a reflecting arrangement (direct beam target).
  • the solidly executed target 23 can absorb a comparatively high power, so that the x-ray tube 11 is advantageously set up to generate a maximum tube current of at least 1 mA and / or a maximum tube power of at least 100 W.
  • the X-ray tube 11 is therefore suitable for testing relatively thick samples such as castings.
  • the invention is not limited to a direct beam target.
  • the filament 17 according to the invention can in particular also be used in an X-ray tube 11 with a transmission target.
  • the maximum tube current is preferably at least 0.5 mA and / or the maximum tube output is at least 50 W.
  • the electron beam 24 is first focused by means of a Wehnelt cylinder or grating 21 lying at a suitable negative potential relative to the filament 17 in order to produce a sharp crossover point 26.
  • the electron-emitting region 28 of the filament 17 is formed by a plurality of loops 29 preferably arranged substantially parallel to one another.
  • the filament 17 in this embodiment is a simple coiled filament.
  • it is at least three loops 29.
  • it is at least three loops 29.
  • it is at least three Loops 29 are shown.
  • the surface of the filament facing the target 23, which is the major source of the electron beam 24, is formed by a plurality of wire sections 30, as best shown in FIG FIG. 4 can be seen.
  • the wire sections 30 are preferably aligned substantially parallel and thus lead to a total planar extension of the surface 23 of the filament 17 facing the target, with a first elongate extension 11 perpendicular to the electron beam and a second elongated extension 12 perpendicular to the electron beam and perpendicular to the extension 11 (please refer FIG. 4 ).
  • Elongated extension means that 11 and 12 are significantly larger than the thickness d of the wire, in particular at least 50% larger, preferably at least twice as large, more preferably at least three times as large, in the present embodiment about four times as large.
  • the extensions 11 and 12 are preferably approximately the same size, ie differ from each other, for example by not more than 50% relative to the larger of the two extensions.
  • the filament 17 is preferably free of points or kinks with a bending radius in the range of the wire diameter d.
  • the loops 29, and thus the electron-emitting wire sections 30, are preferably spaced apart from each other, as in FIG FIG. 4 recognizable.
  • the distance is preferably smaller than or equal to the thickness d of the filament wire 27, and is preferably in the range of 0.1 d to d, in the present case, for example 0.5 d or about 100 microns.
  • the spaced arrangement of the wire sections 30 has the merit that the flanks or side surfaces of the wire sections 30 contribute in addition to the electron emitting surface forming the source of the electron beam. As a result, the effective electron-emitting surface can be further increased without additional effort.
  • each wire section 30 may be formed by a separate simple filament.
  • five wire sections 30 are formed by a serpentine filament.
  • the embodiment according to FIG. 6 illustrates that a total planar extent of the target 23 facing surface of the filament wire 27 can be realized without straight wire sections 30.
  • the X-ray tube 11 is designed in an open design, that is, the tube 11 has means for venting and can be opened in the ventilated state to remove a cathode member 15 and insert a new cathode member 15, especially when a filament reaches or exceeded a predetermined operating time Has.
  • the housing 34 of the X-ray tube 11 consists for this purpose of two housing halves 35, 36, which are separable from each other on a flange 37.
  • the cathode element 15 designed as a replaceable unit comprises the Wehnelt cylinder 21, so that the centering of the filament 17 relative to the front opening 31 for the electron beam 24 can already be made by the manufacturer and does not have to be performed by the operator of the X-ray tube 11.
  • the X-ray tube 11 After inserting a new cathode element 15, the X-ray tube 11 is vacuum-tight closed by connecting the two housing halves 35, 36 and evacuated by means of a permanently mounted on the X-ray tube 11 vacuum pump 33 to the operating vacuum.
  • the x-ray tube 11, especially if a higher detail detectability of the x-ray images is desired, is arranged for optional use with a hairpin filament 17.
  • a cathode element 15 with a Haarnadelfilament in the receptacle 32 to use; the X-ray tube 11 in this high-resolution operating state is in FIG. 7 shown.
  • essential parameters of the filament 17 to be used with the substantially flat extension such as wire length and diameter, dimensions such as, for example, loop diameter and spacing, are optimally adapted.
  • FIG. 1 The embodiment shown relates to a microcomputer tomography system 10.
  • the X-ray tube 11 is also suitable for a two-dimensional radiographic testing system without CT reconstruction.

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  • X-Ray Techniques (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Description

Die Erfindung betrifft eine Mikrofokus-Röntgenröhre mit einem Kathodenelement umfassend ein aus einem Draht gebildetes, heizbares Filament zur Glühemission von Elektronen zur Bildung eines Elektronenstrahls.
In Mikrofokus-Röntgenröhren werden zur Erzielung einer Brennfleckgröße im µm-Bereich Haarnadel-Filamente verwendet, bei denen der Draht zu einer scharfen Spitze gebogen ist, um einen feinen Elektronenstrahl zu emittieren. Aufgrund zunehmend höherer Röhrenströme und damit verbundener Filamenttemperaturen haben Haarnadel-Filamente jedoch nur eine relativ kurze Lebensdauer, weshalb die Kathode regelmäßig nach einer begrenzten Anzahl von Betriebsstunden ausgetauscht werden muss. Hierdurch werden erheblicher zusätzlicher Serviceaufwand und entsprechende Ausfallzeiten verursacht, die insbesondere dem Einsatz von Mikrofokus-Röntgenprüfvorrichtungen in der industriellen Fertigung entgegenstehen.
US 2009 129550 A1 , DE-OS 2 249 365 und US 2005 141670 A1 offenbaren unterschiedliche Kathodenelemente für Röntgenröhren.The invention relates to a microfocus X-ray tube with a cathode element comprising a heatable filament formed from a wire for the glow emission of electrons to form an electron beam.
In microfocus X-ray tubes, hairpin filaments are used to achieve a focal spot size in the micron range, where the wire is bent to a sharp point to emit a fine electron beam. However, due to increasingly higher tube currents and associated filament temperatures, hairpin filaments only have a relatively short life, which is why the cathode must be regularly replaced after a limited number of operating hours. As a result, significant additional service costs and corresponding downtime are caused, which in particular preclude the use of microfocus X-ray inspection devices in industrial production.
US 2009 129550 A1 . DE-OS 2 249 365 and US 2005 141670 A1 disclose different cathode elements for x-ray tubes.

US 6 600 809 B1 offenbart eine Mikrofokus-Röntgenröhre mit einem Haarnadel-Filament. US Pat. No. 6,600,809 B1 discloses a microfocus X-ray tube with a hairpin filament.

Die Aufgabe der Erfindung besteht darin, eine Mikrofokus-Röntgenröhre bereitzustellen, die in für den Benutzer besonders einfacher Weise an unterschiedliche Anwendungsfälle angepasst werden kann.The object of the invention is to provide a microfocus X-ray tube, which can be adapted in a particularly simple way for the user to different applications.

Die Erfindung löst diese Aufgabe mit den Mitteln der unabhängigen Ansprüche. Aufgrund der erfindungsgemäßen länglichen Erstreckung des Filaments, im Quellbereich des Elektronenstrahls, in zwei Richtungen senkrecht zum Elektronenstrahl kann die effektive Elektronen emittierende Fläche signifikant erhöht werden, so dass im Vergleich zu der im Wesentlichen punktförmigen Erstreckung der Elektronen emittierenden Spitze eines HaarnadelFilaments eine erheblich niedrigere Filamenttemperatur zur Emission des gleichen Elektronenstroms ausreicht. Längliche Erstreckung des Filaments bedeutet, dass die Erstreckung signifikant, insbesondere mindestens 50% größer ist als die Dicke des Drahts, vorzugsweise mindestens doppelt so groß, weiter vorzugsweise mindestens drei mal so groß. Die niedrigere Filamenttemperatur führt zu einer erheblichen Verlängerung der Lebensdauer des Filaments und damit des Kathodenelements. Mit der Erfindung lässt sich eine um ein Vielfaches, bis zu einer Größenordnung und mehr, verlängerte Filament-Lebensdauer erzielen. Überraschenderweise hat sich gezeigt, dass trotz der vergrößerten Elektronen emittierenden Fläche dennoch eine Brennpunktgröße von weniger als 10 µm, vorzugsweise 7 µm und weniger, erzielbar ist. Aufgrund der Erfindung ist daher ein Einsatz hochauflösender Mikrofokus-Röntgenprüfvorrichtungen in der industriellen Fertigung möglich.The invention solves this problem with the means of the independent claims. Due to the inventive elongated extension of the filament, in the source region of the electron beam, in two directions perpendicular to the electron beam, the effective electron-emissive surface can be significantly increased, so that a considerably lower filament temperature is sufficient to emit the same electron current as compared to the substantially punctiform extent of the electron-emitting tip of a hairpin filament. Elongation of the filament means that the extent is significantly, in particular at least 50% greater than the thickness of the wire, preferably at least twice as large, more preferably at least three times as large. The lower filament temperature leads to a considerable extension of the life of the filament and thus of the cathode element. With the invention can be achieved by a multiple, up to an order of magnitude and more, extended filament life. Surprisingly, it has been shown that, despite the increased electron-emitting area, a focal point size of less than 10 μm, preferably 7 μm and less, can be achieved. Due to the invention, it is therefore possible to use high-resolution microfocus X-ray inspection devices in industrial production.

Vorzugsweise weist das Filament in dem Quellbereich des Elektronenstrahls eine Mehrzahl von nebeneinander angeordneten Drahtabschnitten auf. Auf diese Weise lässt sich die Erfindung auf einfache Weise aus einem Draht realisieren. In einer besonders einfach zu fertigenden und damit bevorzugten Ausführungsform sind die Drahtabschnitte von einer Mehrzahl von Drahtschleifen gebildet, so dass der Elektronen emittierende Bereich des Filaments die Form einer Drahtwendel hat.Preferably, the filament in the source region of the electron beam on a plurality of juxtaposed wire sections. In this way, the invention can be realized in a simple manner from a wire. In a particularly easy-to-manufacture and thus preferred embodiment, the wire sections are formed by a plurality of wire loops so that the electron-emitting region of the filament has the shape of a wire helix.

Vorzugsweise sind die Drahtabschnitte beabstandet zueinander angeordnet. Dann können die Drahtflanken, d.h. die seitlichen Drahtoberflächen zwischen den Drahtabschnitten, zusätzlich zu der Elektronen emittierenden Fläche beitragen, wodurch der erfindungsgemäße Effekt noch vergrößert werden kann. Vorzugsweise beträgt die Zahl der Drahtabschnitte mindestens drei, um eine erhebliche Vergrößerung der Elektronen emittierenden Fläche zu erreichen. Vorzugsweise beträgt die Zahl der Elektronen emittierenden Drahtabschnitte höchstens zehn, weiter vorzugsweise höchstens sechs, um einen Mikrofokus, d.h. einen Brennfleck des Elektronenstrahls von höchstens 10 µm, erreichen zu können. Eine ungerade Anzahl von Drahtabschnitten ist vorteilhaft, weil aufgrund des einen genau mittigen Drahtabschnitts das Strahlprofil des Elektronenstrahls günstiger wird. Besonders bevorzugt sind drei, fünf oder sieben Drahtabschnitte. Der Erfindung nach ist das Kathodenelement als auswechselbare Einheit zum Einsatz in eine Wechselaufnahme einer Mikrofokus-Röntgenröhre ausgebildet. Folglich kann je nach Anwendung ein erfindungsgemäßes Kathodenelement oder ein Kathodenelement mit einem Haarnadel-Filament in die Wechselaufnahme einer erfindungsgemäßen Mikrofokus-Röntgenröhre eingesetzt werden.Preferably, the wire portions are spaced from each other. Then the wire edges, ie the lateral Contribute wire surfaces between the wire sections, in addition to the electron-emitting surface, whereby the effect according to the invention can be further increased. Preferably, the number of wire sections is at least three in order to achieve a significant increase in the electron-emitting area. The number of electron-emitting wire sections is preferably at most ten, more preferably at most six, in order to be able to achieve a microfocus, ie a focal spot of the electron beam of at most 10 μm. An odd number of wire sections is advantageous because the beam profile of the electron beam becomes more favorable due to the one exactly central wire section. Particularly preferred are three, five or seven wire sections. According to the invention, the cathode element is designed as a replaceable unit for use in an exchange of a microfocus X-ray tube. Consequently, depending on the application, a cathode element according to the invention or a cathode element with a hairpin filament can be inserted into the interchangeable receptacle of a microfocus X-ray tube according to the invention.

Eine erfindungsgemäße Mikrofokus-Röntgenröhre umfasst eine Kondensorlinse, um den Elektronenstrahl im Falle eines erfindungsgemäßen Kathodenelements näherungsweise parallel auszurichten. Dies ermöglicht es, insbesondere unter Verwendung einer nachgeschalteten herkömmlichen Fokussierlinse, die spezifizierten Nenngrößen der Röhre unabhängig vom Typ des eingesetzten Kathodenelements zu erhalten. Die Kondensorlinse wird im Fall eines Kathodenelements mit einem Haarnadel-Filament zweckmäßigerweise ausgeschaltet. Eine Anpassung der Fokussierlinse an das erfindungsgemäße Kathodenelement ist nicht erforderlich.A microfocus X-ray tube according to the invention comprises a condenser lens in order to align the electron beam approximately parallel in the case of a cathode element according to the invention. This makes it possible, in particular using a downstream conventional focusing lens, to obtain the specified nominal sizes of the tube regardless of the type of cathode element used. The condenser lens becomes in the case of a cathode element with a hairpin filament expediently switched off. An adaptation of the focusing lens to the cathode element according to the invention is not required.

Die Erfindung wird im Folgenden anhand vorteilhafter Ausführungsformen unter Bezugnahme auf die beigefügten Figuren erläutert. Dabei zeigt:

Fig. 1
eine schematische Darstellung eines Mikro-Computertomografiesystems;
Fig. 2
eine schematische Querschnittsansicht einer Mikrofokus-Röntgenröhre mit einem eingesetzten Kathodenelement gemäß Figuren 3, 4;
Fig. 3
eine perspektivische Ansicht eines Filaments in einer Ausführungsform der Erfindung;
Fig. 4
eine Ansicht entgegen der Elektronenstrahlrichtung auf eine Kathodeneinheit mit dem in Fig. 3 gezeigten Filament;
Fig. 5,6
Ansichten entgegen der Elektronenstrahlrichtung auf eine Kathodeneinheit mit einem Filament in weiteren Ausführungsformen; und
Fig. 7
eine schematische Querschnittsansicht einer Mikrofokus-Röntgenröhre mit einem eingesetzten Kathodenelement mit Haarnadel-Filament.
The invention will be explained below with reference to advantageous embodiments with reference to the accompanying figures. Showing:
Fig. 1
a schematic representation of a micro-computer tomography system;
Fig. 2
a schematic cross-sectional view of a microfocus X-ray tube with an inserted cathode element according to FIGS. 3, 4 ;
Fig. 3
a perspective view of a filament in an embodiment of the invention;
Fig. 4
a view opposite to the electron beam direction on a cathode unit with the in Fig. 3 shown filament;
Fig. 5.6
View against the electron beam direction on a cathode unit with a filament in further embodiments; and
Fig. 7
a schematic cross-sectional view of a microfocus X-ray tube with an inserted cathode element with hairpin filament.

Die in Figur 1 gezeigte Mikro-Computertomografieanlage umfasst ein Röntgensystem 10, das zur Aufnahme eines Satzes von Röntgenprojektionen einer Probe 13 eingerichtet ist. Zu diesem Zweck umfasst das Röntgensystem 10 eine Mikrofokus-Röntgenröhre 11, die Röntgenstrahlung 14 ausgehend von einem Brennpunkt oder Fokus 16 der Röntgenröhre 11 emittiert, einen bildgebenden Röntgendetektor 12 und einen Probenhalter 20, der vorzugsweise zum Rotieren der Probe 13 um eine vertikale Achse eingerichtet ist. Der Röntgendetektor 12 ist vorzugsweise ein Flächendetektor, insbesondere ein flat panel-Detektor, jedoch ist auch ein Zeilendetektor möglich. Ein Satz von Röntgenprojektionen der Probe 13 wird beispielsweise durch schrittweises Rotieren des Probenhalters 20 um jeweils einen definierten kleinen Winkelschritt und Aufnahme einer Röntgenprojektion bei jedem Rotationswinkel erhalten. Das Röntgensystem 10 ist nicht auf eine Rotation des Probenhalters 20 um eine vertikale Achse beschränkt. Alternativ können beispielsweise die Röntgenröhre 11 und der Röntgendetektor 12 um die feststehende Probe 13 rotiert werden.
Die Röntgenprojektionen werden aus dem Röntgendetektor 12 ausgelesen und an eine Computervorrichtung 41 übermittelt, wo aus dem aufgenommenen Satz von Röntgenprojektionen mittels eines grundsätzlich bekannten Rekonstruktionsalgorithmus rekonstruierte dreidimensionale Volumendaten der Probe 13 errechnet und beispielsweise auf einem Bildschirm 42 dargestellt werden. Die Computervorrichtung 41 kann, wie in Fig. 1 gezeigt, ebenfalls zur Steuerung der Röntgenquelle 11, des Probenhalters 20 und des Röntgendetektors 12 eingerichtet sein; alternativ kann eine separate Steuervorrichtung vorgesehen sein.In the FIG. 1 The microcomputer tomography system shown comprises an x-ray system 10 which is set up to record a set of x-ray projections of a sample 13. To this Purpose X-ray system 10 comprises a microfocus X-ray tube 11 emitting X-radiation 14 from a focal point or focus 16 of X-ray tube 11, an X-ray imaging detector 12, and a sample holder 20 preferably arranged to rotate sample 13 about a vertical axis. The X-ray detector 12 is preferably an area detector, in particular a flat-panel detector, but a line detector is also possible. A set of X-ray projections of the sample 13 is obtained, for example, by stepwise rotating the sample holder 20 by a defined small angle step and recording an X-ray projection at each rotation angle. The X-ray system 10 is not limited to rotation of the sample holder 20 about a vertical axis. Alternatively, for example, the X-ray tube 11 and the X-ray detector 12 may be rotated around the fixed sample 13.
The X-ray projections are read out of the X-ray detector 12 and transmitted to a computer device 41 where reconstructed three-dimensional volume data of the sample 13 are calculated from the recorded set of X-ray projections by means of a basically known reconstruction algorithm and displayed, for example, on a screen 42. The computing device 41 may, as in Fig. 1 also be arranged to control the X-ray source 11, the sample holder 20 and the X-ray detector 12; Alternatively, a separate control device may be provided.

Die Mikrofokus-Röntgenröhre 11 umfasst ein Kathodenelement 15, einen Wehnelt-Zylinder 21, eine Anode 19, eine vorzugsweise als elektromagnetische Linse ausgeführte Fokussierlinse 22 und ein Elektronenstrahl-Target 23. Des Weiteren kann eine weitere elektromagnetische Linse 25 vorgesehen sein, die als Kondensorlinse eingerichtet ist, um den Elektronenstrahl 24 näherungsweise parallel auszurichten. Die Mikrofokus-Röntgenröhre 11 umfasst weiterhin zweckmäßigerweise eine nicht gezeigte Ablenkeinheit zur Strahllagejustierung. Das Kathodenelement 15 umfasst ein Filament 17, das aus einem geeigneten Draht 27, insbesondere aus Wolfram, besteht und auf einem isolierenden, beispielsweise aus einer Keramik bestehenden Sockel 34 montiert ist. Der Filamentdraht 27 weist vorzugsweise eine Stärke im Bereich von 100 µm bis 300 µm, beispielsweise etwa 200 µm, auf. An die Enden des Filaments 17 wird eine Heizspannung zur Glühemission von Elektronen aus dem Filamentdraht 27 angelegt. Zwischen das Filament 17 und die Anode 19 wird eine mit einem nicht gezeigten Hochspannungsgenerator erzeugte Beschleunigungsspannung angelegt, um die aus dem Draht extrahierten Elektronen zur Anode 19 hin zu beschleunigen und einen Elektronenstrahl 24 zu erzeugen. Die maximale Beschleunigungsspannung beträgt vorzugsweise mindestens 100 kV, vorzugsweise mindestens 200 kV.
Der erzeugte Elektronenstrahl wird mittels der Fokussierlinse 22 auf das Target 23 fokussiert, wodurch die Röntgenstrahlung 14 erzeugt wird. Das Target 23 ist vorzugsweise in einer reflektierenden Anordnung angeordnet (Direktstrahltarget). Das massiv ausgeführte Target 23 kann eine vergleichsweise hohe Leistung aufnehmen, so dass die Röntgenröhre 11 vorteilhafterweise zur Erzeugung eines maximalen Röhrenstroms von mindestens 1 mA und/oder einer maximalen Röhrenleistung von mindestens 100 W eingerichtet ist. Die Röntgenröhre 11 ist daher zur Prüfung von relativ dicken Proben wie etwa Gussteilen geeignet.The microfocus X-ray tube 11 comprises a cathode element 15, a Wehnelt cylinder 21, an anode 19, a focusing lens 22, preferably embodied as an electromagnetic lens, and an electron beam target 23. Furthermore, a further electromagnetic lens 25 may be provided. which is arranged as a condenser lens to align the electron beam 24 approximately parallel. The microfocus X-ray tube 11 further expediently comprises a deflection unit (not shown) for adjusting the beam position. The cathode element 15 comprises a filament 17, which consists of a suitable wire 27, in particular of tungsten, and is mounted on an insulating, for example made of a ceramic base 34. The filament wire 27 preferably has a thickness in the range of 100 microns to 300 microns, for example, about 200 microns, on. At the ends of the filament 17, a heating voltage is applied to the glow emission of electrons from the filamentary wire 27. Between the filament 17 and the anode 19, an acceleration voltage generated by a high-voltage generator, not shown, is applied to accelerate the electrons extracted from the wire toward the anode 19 and to generate an electron beam 24. The maximum acceleration voltage is preferably at least 100 kV, preferably at least 200 kV.
The generated electron beam is focused by means of the focusing lens 22 on the target 23, whereby the X-ray radiation 14 is generated. The target 23 is preferably arranged in a reflecting arrangement (direct beam target). The solidly executed target 23 can absorb a comparatively high power, so that the x-ray tube 11 is advantageously set up to generate a maximum tube current of at least 1 mA and / or a maximum tube power of at least 100 W. The X-ray tube 11 is therefore suitable for testing relatively thick samples such as castings.

Die Erfindung ist nicht auf ein Direktstrahltarget beschränkt. Das erfindungsgemäße Filament 17 kann insbesondere auch in einer Röntgenröhre 11 mit einem Transmissionstarget verwendet werden. Im Hinblick darauf beträgt der maximale Röhrenstrom vorzugsweise mindestens 0.5 mA und/oder die maximale Röhrenleistung mindestens 50 W.
Um die in der Mikro-Computertomografie gewünschte Detailerkennbarkeit im Röntgenbild von deutlich unter 10 µm zu erzielen, ist es erforderlich, dass die Größe des Elektronenstrahl-Brennflecks 16 auf dem Target 23 unterhalb von 10 µm liegt. Zu diesem Zweck wird der Elektronenstrahl 24 zunächst mittels eines auf einem geeigneten negativen Potential relativ zu dem Filament 17 liegenden Wehnelt-Zylinders bzw. Gitters 21 fokussiert, um einen scharfen Crossover-Punkt 26 zu erzeugen. Kathode 17, Wehnelt-Zylinder 21 und Anode 19 bildet somit eine Triode. Hinter der Anode 19 wird der Elektronenstrahl des Weiteren mit einer Fokussierlinse 22 auf den Brennpunkt 16 des Targets fokussiert. Verallgemeinert ist die Elektronenoptik der Röhre 11, hier bestehend aus Wehnelt-Zylinder 21, Fokussierlinse 22 und Kondensorlinse 25, zur Erzeugung eines Brennflecks 16 mit einem mittleren Durchmesser von höchsten 10 µm eingerichtet.
In einer bevorzugten Ausführungsform gemäß den Figur 3 und 4 wird der Elektronen emittierende Bereich 28 des Filaments 17 von einer Mehrzahl von vorzugsweise im Wesentlichen parallel zueinander angeordneten Schleifen 29 gebildet. Das Filament 17 ist in dieser Ausführungsform eine einfach gewendelte Glühwendel. Vorzugsweise handelt es sich um mindestens drei Schleifen 29. Im Ausführungsbeispiel der Figuren 3 und 4 sind drei Schleifen 29 gezeigt. Vorzugsweise handelt es sich weiterhin um höchstens zehn Schleifen 29, weiter vorzugsweise um höchstens sieben Schleifen 29, um die Ausdehnung des Elektronen emittierenden Bereichs im Hinblick auf die gewünschte Detailerkennbarkeit im Röntgenbild zu begrenzen.The invention is not limited to a direct beam target. The filament 17 according to the invention can in particular also be used in an X-ray tube 11 with a transmission target. In this regard, the maximum tube current is preferably at least 0.5 mA and / or the maximum tube output is at least 50 W.
In order to achieve the detail recognition in the X-ray image of significantly below 10 μm desired in microcomputer tomography, it is necessary for the size of the electron beam focal spot 16 on the target 23 to be below 10 μm. For this purpose, the electron beam 24 is first focused by means of a Wehnelt cylinder or grating 21 lying at a suitable negative potential relative to the filament 17 in order to produce a sharp crossover point 26. Cathode 17, Wehnelt cylinder 21 and anode 19 thus forms a triode. Behind the anode 19, the electron beam is further focused with a focusing lens 22 on the focal point 16 of the target. Generalized is the electron optics of the tube 11, here consisting of Wehnelt cylinder 21, focusing lens 22 and condenser lens 25, set up to produce a focal spot 16 with a mean diameter of 10 microns maximum.
In a preferred embodiment according to the FIGS. 3 and 4 For example, the electron-emitting region 28 of the filament 17 is formed by a plurality of loops 29 preferably arranged substantially parallel to one another. The filament 17 in this embodiment is a simple coiled filament. Preferably, it is at least three loops 29. In the embodiment of the FIGS. 3 and 4 are three Loops 29 are shown. Furthermore, preferably at most ten loops 29, more preferably at most seven loops 29, in order to limit the extent of the electron-emitting region with regard to the desired detail recognition in the X-ray image.

Die dem Target 23 zugewandte Oberfläche des Filaments, die die hauptsächliche Quelle des Elektronenstrahls 24 bildet, wird von einer Mehrzahl von Drahtabschnitten 30 gebildet, wie am besten in Figur 4 zu erkennen ist. Die Drahtabschnitte 30 sind vorzugsweise im Wesentlichen parallel ausgerichtet und führen somit zu einer insgesamt flächigen Erstreckung der dem Target 23 zugewandte Oberfläche des Filaments 17, mit einer ersten länglichen Erstreckung 11 senkrecht zum Elektronenstrahl und einer zweiten länglichen Erstreckung 12 senkrecht zum Elektronenstrahl und senkrecht zur Erstreckung 11 (siehe Figur 4). Längliche Erstreckung bedeutet, dass 11 und 12 signifikant größer sind als die Dicke d des Drahts, insbesondere mindestens 50% größer, vorzugsweise mindestens doppelt so groß, weiter vorzugsweise mindestens drei mal so groß, im vorliegenden Ausführungsbeispiel etwa viermal so groß. Im Vergleich zu der "punktförmigen" Oberfläche der Spitze eines Haarnadelfilaments mit einer Erstreckung von etwa d2 ergibt sich eine um bis zu einen Faktor drei und mehr vergrößerte Elektronen emittierende Oberfläche des Filaments 17. Zur Erzeugung des gleichen Röhrenstromes kann damit die Heiztemperatur des Filaments 17 erheblich abgesenkt und damit dessen Lebensdauer um bis zu einem Faktor zehn und mehr erhöht werden. Die Erstreckungen 11 und 12 sind vorzugsweise etwa gleich groß, d.h. unterscheiden sich voneinander beispielsweise um nicht mehr als 50% bezogen auf die größere der beiden Erstreckungen. Das Filament 17 ist vorzugsweise frei von Spitzen bzw. Knickstellen mit einem Biegeradius im Bereich des Drahtdurchmessers d.The surface of the filament facing the target 23, which is the major source of the electron beam 24, is formed by a plurality of wire sections 30, as best shown in FIG FIG. 4 can be seen. The wire sections 30 are preferably aligned substantially parallel and thus lead to a total planar extension of the surface 23 of the filament 17 facing the target, with a first elongate extension 11 perpendicular to the electron beam and a second elongated extension 12 perpendicular to the electron beam and perpendicular to the extension 11 (please refer FIG. 4 ). Elongated extension means that 11 and 12 are significantly larger than the thickness d of the wire, in particular at least 50% larger, preferably at least twice as large, more preferably at least three times as large, in the present embodiment about four times as large. Compared to the "dot-shaped" surface of the tip of a Haarnadelfilaments with an extension of about d 2 results in up to a factor of three and more enlarged electron-emitting surface of the filament 17. To produce the same tube current so that the heating temperature of the filament 17th significantly lowered and thus its life can be increased by a factor of ten or more. The extensions 11 and 12 are preferably approximately the same size, ie differ from each other, for example by not more than 50% relative to the larger of the two extensions. The filament 17 is preferably free of points or kinks with a bending radius in the range of the wire diameter d.

Die Schleifen 29, und damit die Elektronen emittierenden Drahtabschnitte 30, sind vorzugsweise beabstandet voneinander angeordnet, wie in Figur 4 erkennbar. Der Abstand ist vorzugsweise kleiner oder gleich der Dicke d des Filamentdrahtes 27, und liegt vorzugsweise im Bereich von 0.1 d bis d, im vorliegenden Fall beispielsweise bei 0.5 d oder etwa 100 µm. Die beabstandete Anordnung der Drahtabschnitte 30 hat den Vorzug, dass die Flanken bzw. die seitlichen Oberflächen der Drahtabschnitte 30 zusätzlich zu der Elektronen emittierenden, die Quelle des Elektronenstrahls bildenden Fläche beitragen. Hierdurch kann die effektive Elektronen emittierende Fläche ohne Mehraufwand noch weiter erhöht werden.The loops 29, and thus the electron-emitting wire sections 30, are preferably spaced apart from each other, as in FIG FIG. 4 recognizable. The distance is preferably smaller than or equal to the thickness d of the filament wire 27, and is preferably in the range of 0.1 d to d, in the present case, for example 0.5 d or about 100 microns. The spaced arrangement of the wire sections 30 has the merit that the flanks or side surfaces of the wire sections 30 contribute in addition to the electron emitting surface forming the source of the electron beam. As a result, the effective electron-emitting surface can be further increased without additional effort.

Die Drahtabschnitte 30 können auch auf andere Weise als mittels Drahtschleifen 29 gebildet werden. In einer nicht gezeigten Ausführungsform kann beispielsweise jeder Drahtabschnitt 30 von einem separaten einfachen Filament gebildet sein. In der in Fig. 5 gezeigten Ausführungsform werden beispielsweise fünf Drahtabschnitte 30 von einem schlangenförmigen Filament gebildet. Die Ausführungsform gemäß Figur 6 verdeutlicht, dass eine insgesamt flächigen Erstreckung der dem Target 23 zugewandte Oberfläche des Filamentdrahts 27 auch ohne gerade Drahtabschnitte 30 realisiert werden kann.The wire sections 30 may also be formed in other ways than by means of wire loops 29. In an embodiment not shown, for example, each wire section 30 may be formed by a separate simple filament. In the in Fig. 5 In the embodiment shown, for example, five wire sections 30 are formed by a serpentine filament. The embodiment according to FIG. 6 illustrates that a total planar extent of the target 23 facing surface of the filament wire 27 can be realized without straight wire sections 30.

Die Röntgenröhre 11 ist in offener Bauform ausgeführt, das heißt die Röhre 11 weist Einrichtungen zum Belüften auf und kann im belüfteten Zustand geöffnet werden, um ein Kathodenelement 15 zu entnehmen und ein neues Kathodenelement 15 einzusetzen, insbesondere wenn ein Filament eine vorbestimmte Betriebsdauer erreicht oder überschritten hat. Das Gehäuse 34 der Röntgenröhre 11 besteht zu diesem Zweck aus zwei Gehäusehälften 35, 36, die an einem Flansch 37 voneinander trennbar sind. Das als auswechselbare Einheit ausgeführte Kathodenelement 15 umfasst den Wehnelt-Zylinder 21, damit die Zentrierung des Filaments 17 relativ zu der stirnseitigen Öffnung 31 für den Elektronenstrahl 24 bereits herstellerseitig erfolgen kann und nicht vom Betreiber der Röntgenröhre 11 durchgeführt werden muss. Nach dem Einsetzen eines neuen Kathodenelements 15 wird die Röntgenröhre 11 durch Verbinden der beiden Gehäusehälften 35, 36 vakuumdicht verschlossen und mittels einer an der Röntgenröhre 11 dauerhaft montierten Vakuumpumpe 33 auf das Betriebsvakuum evakuiert.
In einer bevorzugten Ausführungsform ist die Röntgenröhre 11, insbesondere wenn eine höhere Detailerkennbarkeit der Röntgenbilder erwünscht ist, zur optionalen Verwendung mit einem Haarnadel-Filament 17 eingerichtet. Zu diesem Zweck ist lediglich ein Kathodenelement 15 mit einem Haarnadelfilament in die Aufnahme 32 einzusetzen; die Röntgenröhre 11 in diesem hochauflösende Betriebszustand ist in Figur 7 gezeigt. Einer weiteren baulichen Veränderung der Röntgenröhre 11, abgesehen vom Austausch des Kathodenelements 15, oder des nicht gezeigten Hochspannungsgenerators bedarf es nicht. Um dies zu ermöglichen, sind wesentliche Parameter des zu verwendenden Filaments 17 mit der im Wesentlichen flächigen Erstreckung, wie Drahtlänge und -durchmesser, Abmessungen wie beispielsweise Schleifendurchmesser sowie Abstände, optimal angepasst. Beim Betrieb der Röntgenröhre 11 mit einem Haarnadelfilament wird die Kondensorlinse 25 ausgeschaltet. Die Röntgenröhre 11 wird daher in herkömmlicher Weise mit der Fokussierlinse 22 betrieben. Das Ausschalten der Kondensorlinse 25 erfolgt automatisch infolge des Einsetzens eines Kathodenelements mit einem Haarnadelfilament.The X-ray tube 11 is designed in an open design, that is, the tube 11 has means for venting and can be opened in the ventilated state to remove a cathode member 15 and insert a new cathode member 15, especially when a filament reaches or exceeded a predetermined operating time Has. The housing 34 of the X-ray tube 11 consists for this purpose of two housing halves 35, 36, which are separable from each other on a flange 37. The cathode element 15 designed as a replaceable unit comprises the Wehnelt cylinder 21, so that the centering of the filament 17 relative to the front opening 31 for the electron beam 24 can already be made by the manufacturer and does not have to be performed by the operator of the X-ray tube 11. After inserting a new cathode element 15, the X-ray tube 11 is vacuum-tight closed by connecting the two housing halves 35, 36 and evacuated by means of a permanently mounted on the X-ray tube 11 vacuum pump 33 to the operating vacuum.
In a preferred embodiment, the x-ray tube 11, especially if a higher detail detectability of the x-ray images is desired, is arranged for optional use with a hairpin filament 17. For this purpose, only a cathode element 15 with a Haarnadelfilament in the receptacle 32 to use; the X-ray tube 11 in this high-resolution operating state is in FIG. 7 shown. A further structural change of the X-ray tube 11, apart from the replacement of the cathode element 15, or the high-voltage generator, not shown, is not required. In order to make this possible, essential parameters of the filament 17 to be used with the substantially flat extension, such as wire length and diameter, dimensions such as, for example, loop diameter and spacing, are optimally adapted. When operating the X-ray tube 11 with a Haarnadelfilament the condenser lens 25 is turned off. The X-ray tube 11 is therefore operated in a conventional manner with the focusing lens 22. Turning off the condenser lens 25 is automatic due to the insertion of a cathode member having a hairpin filament.

Die in Figur 1 gezeigte Ausführungsform betrifft ein Mikro-Computertomografieanlage 10. Die Röntgenröhre 11 ist jedoch ebenfalls für eine zweidimensionale Durchstrahlungsprüfanlage ohne CT-Rekonstruktion geeignet.In the FIG. 1 The embodiment shown relates to a microcomputer tomography system 10. However, the X-ray tube 11 is also suitable for a two-dimensional radiographic testing system without CT reconstruction.

Claims (8)

  1. A microfocus X-ray tube (11), comprising a cathode element (15), the cathode element (15) comprising:
    a heatable filament (17) consisting of a wire (27), for the thermionic emission of electrons for forming an electron beam (24), wherein the filament (17), in a source area of the electron beam (24), has an elongate extent, respectively, in two directions perpendicular to the electron beam,
    and a Wehnelt cylinder (21) with an end-side opening, configured for focusing the electron beam,
    wherein the cathode element (15) is configured as a replaceable unit for insertion into an exchange-enabling mounting (32) of the microfocus X-ray tube (11),
    wherein the filament (17) of the cathode element (15) is centered relative to the end-side opening already in the replaceable unit,
    wherein the microfocus X-ray tube (11) further includes a target (23) for generating X-radiation (14) as a result of the electron beam (24) hitting the target (23), and
    wherein the microfocus X-ray tube (11) includes a condenser lens (25) configured to orientate the electron beam (24) approximately parallel, wherein the condenser lens (25) can be switched off automatically as a consequence of a cathode element with a hairpin filament being inserted into the exchange-enabling mounting (32).
  2. The microfocus X-ray tube (11) according to claim 1, wherein the microfocus X-ray tube (11) can be vented, opened and sealed to be vacuum-tight for replacing the cathode unit.
  3. The microfocus X-ray tube (11) according to claim 1 or 2, comprising a vacuum pump (33) for evacuating the microfocus X-ray tube.
  4. The microfocus X-ray tube according to any one of the claims 1 to 3, wherein the filament (17) has a plurality of wire portions (30) disposed laterally side-by-side in the source area (28) of the electron beam (24).
  5. The microfocus X-ray tube (11) according to claim 4, wherein the wire portions (30) are disposed so as to be spaced apart from one another.
  6. The microfocus X-ray tube (11) according to claim 4 or 5, wherein the number of the wire portions (30) is at least three.
  7. The microfocus X-ray tube (11) according to any one of the claims 2 to 6, wherein the wire portions (30) are formed by a plurality of wire loops (29) of the filament wire (27).
  8. A method for the microfocus X-ray inspection of a sample, comprising the generation of X-radiation using a microfocus X-ray tube (11) according to any one of the claims 1 to 7, and further comprising:
    removing the cathode element (15) from the exchange-enabling mounting (32) of the microfocus X-ray tube (11), and
    inserting a cathode element with a hairpin filament into the exchange-enabling mounting (32), wherein the condenser lens (25) of the microfocus X-ray tube (11) is switched off automatically as a consequence of the insertion of the cathode element with a hairpin filament into the exchange-enabling mounting (32).
EP10716475.8A 2010-04-09 2010-04-09 Microfocus x-ray tube with cathode element and process using the same Active EP2556525B1 (en)

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WO2011124237A1 (en) 2011-10-13
US9601300B2 (en) 2017-03-21

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