EP0063840B1 - High tension vacuum tube, particularly x ray tube - Google Patents

High tension vacuum tube, particularly x ray tube Download PDF

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Publication number
EP0063840B1
EP0063840B1 EP82200452A EP82200452A EP0063840B1 EP 0063840 B1 EP0063840 B1 EP 0063840B1 EP 82200452 A EP82200452 A EP 82200452A EP 82200452 A EP82200452 A EP 82200452A EP 0063840 B1 EP0063840 B1 EP 0063840B1
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EP
European Patent Office
Prior art keywords
insulator
electrode
conductive part
shielding electrode
vacuum tube
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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.)
Expired
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EP82200452A
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German (de)
French (fr)
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EP0063840A1 (en
Inventor
Horst Dr. Brettschneider
Walter Dr. Hartl
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Philips Intellectual Property and Standards GmbH
Koninklijke Philips NV
Original Assignee
Philips Patentverwaltung GmbH
Philips Gloeilampenfabrieken NV
Koninklijke Philips Electronics NV
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Publication of EP0063840A1 publication Critical patent/EP0063840A1/en
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    • 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
    • H01J1/52—Screens for shielding; Guides for influencing the discharge; Masks interposed in the electron stream
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details

Definitions

  • the invention relates to a high-voltage vacuum tube, in particular an X-ray tube, with an electrode located in its vacuum space which, in the operating state, carries positive high voltage with respect to an electrically conductive part which at least partially surrounds it, the electrode or a part connected to it having the conductive one Part is connected via an insulator.
  • Such a high-voltage vacuum tube is known from DE-OS 2 506 841.
  • the electrode is generally the anode of the high-voltage vacuum tube.
  • the electrode can also be the shaft carrying the same potential as the anode disk and carrying the anode disk.
  • the electrically conductive part is usually the metal tube bulb of such a tube or a part thereof.
  • it can also be a metal cylinder which rotates together with an insulator and the shaft of the rotating anode disc and is connected to the housing of the x-ray tube via a bearing, as is known from DE-PS 2 455 974.
  • the insulator is shaped in such a way that its truncated cone-shaped inner jacket widens in the axial direction from the connection area with the electrode.
  • the shape of the isolator means that discharge processes on the isolator surface are prevented, which could reduce the operational reliability of the tube.
  • the binding energy of gas layers adsorbed on the surface is reduced by the increased temperature of the insulator, so that desorption stimulated by electrons can take place to an increased extent and discharge processes can thereby be initiated (RA Anderson, JP Brainard; Mechanism of pulsed surface flashover involving electron-stimulated desorption, J. Appl. Phys. 51, 1414, (1980).
  • the object of the present invention is to design a high-voltage vacuum tube of the type mentioned at the outset in such a way that the described discharge processes are largely prevented even when subjected to high thermal loads.
  • This object is achieved according to the invention by the measures specified in the characterizing part of the main claim.
  • the inventors have recognized that the described discharge processes in the operating state under high thermal stress have their origin in the area of the connection between the insulator and the conductive part, which is exposed to the electric field between the conductive part and the electrode, especially if in this area the insulator is brazed to the electrically conductive part. Because the shielding electrode reduces the electric field in this area, the described discharge processes are largely prevented.
  • the shielding electrode itself cannot become the starting point for the described discharge processes, it must be shaped and arranged in such a way that the electrons emitted by it largely cannot hit the inner surface of the insulator which is exposed to a strong electric field in the operating state.
  • a vacuum tube in the form of a magnetic field tube is already known from US-PS 4205250, with an electrode located in its vacuum space, which is mechanically connected via a cup-shaped insulator to a conductive cylinder surrounding it, in the connection area a shielding electrode is provided between the insulator and the conductive cylinder.
  • magnetrons generate a magnetic field in the axial direction and the electrode has a negative potential with respect to the cylinder. Since the connection between the conductive cylinder or electrode and the insulator takes place with the aid of a ferromagnetic intermediate piece or a ferromagnetic metal connection (Kovar), such a magnetic field tube results in a magnetic leakage flux between the connections mentioned.
  • the shielding electrode which can in principle also be replaced by a shielding electrode in the area of the connection between the electrode and the insulator, must now be shaped in such a way that it cuts the path of the charged particles between the two connection areas and the charged particles on their path on them can hit.
  • the electrode has a positive potential (however) with respect to the conductive cylinder, this shape is disadvantageous from a high-voltage point of view because electrons emitted from the shielding electrode can strike the inner surface of the insulator, where they cause discharge processes on the surface of the insulator.
  • the insulator is shaped in such a way that a cavity which is open between the shielding electrode and the conductive part is enclosed.
  • the area of the connection point between the insulator and the conductive part is largely protected against discharge carriers which run through the gap between the shielding electrode and the insulator in the direction of the electrically conductive part, so that the discharge processes can be prevented particularly effectively.
  • Fig. 1 shows an X-ray tube
  • the piston 1 is made entirely of metal.
  • the piston 1 is essentially rotationally symmetrical.
  • the anode disk 2 has a flattened focal spot path, which is arranged opposite the cathode 3, which is connected via an insulator 4 to a metal cylinder 5, which in turn is connected to the piston having an opening in this area.
  • the anode is held in two places.
  • a pin 6 is provided which is concentric with the axis of rotation and which carries a bearing 7 which is connected to the cylindrical rotor 9 via a ring 8.
  • the pin 6, the bearing 7 and the ring 8 establish a conductive connection between the piston 1 and the rotor 9, so that the rotor is also grounded to the metal piston.
  • the ring 8 and with it the rotor 9 is connected via a further ring 15 to an insulator 11 which is fastened on a shaft 12 carrying the anode disk 2.
  • the supply of the high voltage to the anode takes place via a further bearing 13, which is mounted in an insulator 14 connected to the tubular bulb 1, which has a conical opening 16 for receiving a high-voltage plug.
  • the ball bearing 13 serves to support the shaft 12. The high voltage is thus supplied to the anode disk 2 via the bearing 13 and the shaft 12.
  • the critical area is the area 17 in which the piston 1, the insulator 14 and the vacuum in the tube adjoin one another. This area, which, as the drawing suggests, cannot be limited to one point, but rather concentrically surrounds the shaft 12, is exposed to the electric field between the piston 1 and the shaft 12. If the thermal load is excessive, it can reach temperatures of well over 100 ° C.
  • FIG. 2 shows a part of the metal piston with the insulator 14 in a partially broken-away representation on a larger scale compared to FIG. 1 with the shielding electrode according to the invention.
  • the ring-shaped shielding electrode 18 is located in the immediate vicinity of the end of the insulator, in which the critical region 17 is located, in which the piston 1, the insulator and the vacuum adjoin one another.
  • the shielding electrode is preferably made of pure iron or another metal, e.g. CrNi steel, and is welded concentrically to the shaft 12 on the inside of the metal piston 1.
  • Both the shielding electrode and the insulator are shaped such that they each form a groove-shaped cavity 21 or 20 with the piston 1, which is open towards the insulator or the shielding electrode.
  • This design on the one hand reduces the field strength in the critical area and on the other hand the charge carriers passing through the gap between the shielding electrode 18 and the insulator 14 cannot hit this critical area directly.
  • the gap between the mutually facing ends of the insulator 14 and the shielding electrode 18 is approximately 1 mm. However, it should not exceed 3 mm. However, if it is significantly smaller than 0.5 mm, then very high field strengths result in this gap, which can lead to field emission on the surface of the shielding electrode 18. In addition, the shielding electrode can then be poorly conditioned. If it is significantly larger than 3 mm, then the electric field in the critical area between metal piston 1, insulator 14 and vacuum is hardly reduced by the shielding electrode 18.
  • the shielding electrode is expediently e.g. treated by electropolishing so that there are hardly any emission centers on its surface.
  • the electrode 18 should be arranged so that electrons emitted from it run directly to the shaft 12 and cannot reach the insulator.
  • the shielding electrode is expediently arranged in a reset manner, i.e. its inner diameter is dimensioned such that the frustoconical inner jacket surface of the insulator 14, which extends towards the shielding electrode or its extension, indicated by lines 19, does not intersect the shielding electrode 18.
  • FIG. 3 shows a section of an X-ray tube according to the invention.
  • the mutually facing end faces 22 and 23 of the insulator 14 and the shielding electrode 18 are approximately flat and run approximately perpendicular to the wall of the metal piston 1. This does indeed reduce the field strength in the critical zone between the piston, the insulator 14 and the vacuum, however, charge carriers passing through the gap can reach this zone directly. This embodiment is therefore not quite as effective as that shown in FIG. 2.
  • the shielding electrode 18 is shaped similarly to that in FIG. it encloses with the wall of the piston 1 a groove-shaped, circumferential cavity 21 which is open towards the insulator 14 and into which a comparatively thin end of the insulator 14 projects.
  • the invention has been explained above in connection with a fixed insulator, it can in principle also be used with a rotating insulator. If, for example in FIG. 1, the grounded metal ring 15 were so long that there would be an area or a zone in which the vacuum space, the metal ring 15 and the insulator 11 adjoin one another and into which that between the metal ring 15 and the shaft 12 would intervene effective electrical field, the invention could also be applied accordingly.
  • the insulator is shaped in such a way that the electrons striking in the operating state find an electric field at least on a substantial part of its surface, which moves it away from the insulator surface, because the truncated cone-shaped inner jacket of the insulator extends in the axial direction from the connection area with the Electrode expanded.
  • the invention can also be applied to an insulator arrangement which is provided with a concentric trough and has an insulator part which is enclosed by the trough and carries the electrode, and an outer insulator part which surrounds the trough and with the conductive part (the tubular bulb or the rotor) is connected.
  • the invention is also not limited to rotating anode X-ray tubes. Rather, it can also be used with other X-ray tubes and with other high-voltage vacuum tubes (e.g. neutron tubes).

Description

Die Erfindung bezieht sich auf eine Hochspannungs-Vakuumröhre, insbesondere eine Röntgenröhre, mit einer in ihrem Vakuumraum befindlichen Elektrode, die im Betriebszustand gegenüber einem sie wenigstens teilweise umschliessenden elektrisch leitenden Teil positive Hochspannung führt, wobei die Elektrode oder ein mit ihr verbundener Teil mit dem leitfähigen Teil über einen Isolator verbunden ist.The invention relates to a high-voltage vacuum tube, in particular an X-ray tube, with an electrode located in its vacuum space which, in the operating state, carries positive high voltage with respect to an electrically conductive part which at least partially surrounds it, the electrode or a part connected to it having the conductive one Part is connected via an insulator.

Eine solche Hochspannungs-Vakuumröhre ist aus der DE-OS 2 506 841 bekannt. Die Elektrode ist dabei im allgemeinen die Anode der Hochspannungs-Vakuumröhre. Bei Drehanoden-Röntgenröhren kann die Elektrode aber auch die das gleiche Potential wie die Anodenscheibe führende, die Anodenscheibe tragende Welle sein. Der elektrisch leitende Teil ist in der Regel der aus Metall bestehende Röhrenkolben einer solchen Röhre bzw. ein Teil davon. Es kann jedoch auch - bei Drehanoden-Röntgenröhren - ein Metallzylinder sein, der zusammen mit einem Isolator und der Welle der Drehanodenscheibe rotiert und über ein Lager mit dem Gehäuse der Röntgenröhre verbunden ist, wie aus der DE-PS 2 455 974 bekannt. Der Isolator ist in der Regel so geformt, dass sein kegelstumpfförmiger Innenmantel sich in Achsrichtung von dem Verbindungsbereich mit der Elektrode aus erweitert.Such a high-voltage vacuum tube is known from DE-OS 2 506 841. The electrode is generally the anode of the high-voltage vacuum tube. In the case of rotating anode X-ray tubes, however, the electrode can also be the shaft carrying the same potential as the anode disk and carrying the anode disk. The electrically conductive part is usually the metal tube bulb of such a tube or a part thereof. However, in the case of rotating anode x-ray tubes, it can also be a metal cylinder which rotates together with an insulator and the shaft of the rotating anode disc and is connected to the housing of the x-ray tube via a bearing, as is known from DE-PS 2 455 974. As a rule, the insulator is shaped in such a way that its truncated cone-shaped inner jacket widens in the axial direction from the connection area with the electrode.

Bei der bekannten Hochspannungs-Vakuumröhre wird durch die Formgebung des Isolators erreicht, dass Entladungsvorgänge auf der Isolatoroberfläche unterbunden werden, die die Betriebssicherheit der Röhre herabsetzen könnten. Bei thermisch stark belasteten Röhren wird jedoch durch die erhöhte Temperatur des Isolators die Bindungsenergie von auf der Oberfläche adsorbierten Gasschichten herabgesetzt, so dass durch Elektronen stimulierte Desorption in erhöhtem Masse stattfinden kann und dadurch Entladungsvorgänge eingeleitet werden (R.A. Anderson, J.P. Brainard; Mechanism of pulsed surface flashover involving electron-stimulated desorption, J. Appl. Phys. 51, 1414, (1980).In the known high-voltage vacuum tube, the shape of the isolator means that discharge processes on the isolator surface are prevented, which could reduce the operational reliability of the tube. In the case of tubes with high thermal loads, however, the binding energy of gas layers adsorbed on the surface is reduced by the increased temperature of the insulator, so that desorption stimulated by electrons can take place to an increased extent and discharge processes can thereby be initiated (RA Anderson, JP Brainard; Mechanism of pulsed surface flashover involving electron-stimulated desorption, J. Appl. Phys. 51, 1414, (1980).

Aufgabe der vorliegenden Erfindung ist es, eine Hochspannungs-Vakuumröhre der eingangs genannten Art so auszugestalten, dass auch bei starker thermischer Belastung die beschriebenen Entladungsvorgänge weitgehend unterbunden werden. Diese Aufgabe wird erfindungsgemäss durch die im kennzeichnenden Teil des Hauptanspruches angegebenen Massnahmen gelöst.The object of the present invention is to design a high-voltage vacuum tube of the type mentioned at the outset in such a way that the described discharge processes are largely prevented even when subjected to high thermal loads. This object is achieved according to the invention by the measures specified in the characterizing part of the main claim.

Die Erfinder haben erkannt, dass die geschilderten Entladungsvorgänge im Betriebszustand bei starker thermischer Belastung ihren Ursprung in dem Bereich der Verbindung zwischen dem Isolator und dem leitenden Teil haben, der dem elektrischen Feld zwischen dem leitenden Teil und der Elektrode ausgesetzt ist, insbesondere wenn in diesem Bereich der Isolator durch eine Hartlötung an den elektrisch leitenden Teil angelötet ist. Dadurch, dass die Abschirmelektrode das elektrische Feld in diesem Bereich herabsetzt, werden die geschilderten Entladungsvorgänge weitgehend unterbunden.The inventors have recognized that the described discharge processes in the operating state under high thermal stress have their origin in the area of the connection between the insulator and the conductive part, which is exposed to the electric field between the conductive part and the electrode, especially if in this area the insulator is brazed to the electrically conductive part. Because the shielding electrode reduces the electric field in this area, the described discharge processes are largely prevented.

Damit die Abschirmelektrode selbst nicht Ausgangspunkt der beschriebenen Entladungsvorgänge werden kann, muss sie so geformt und angeordnet sein, dass von ihr emittierte Elektronen grösstenteils nicht auf die im Betriebszustand einem starken elektrischen Feld ausgesetzte Innenfläche des Isolators treffen können.So that the shielding electrode itself cannot become the starting point for the described discharge processes, it must be shaped and arranged in such a way that the electrons emitted by it largely cannot hit the inner surface of the insulator which is exposed to a strong electric field in the operating state.

Es sei an dieser Stelle erwähnt, dass aus der US-PS 4205250 bereits eine Vakuumröhre in Form einer Magnetfeldröhre bekannt ist, mit einer in ihrem Vakuumraum befindlichen Elektrode, die über einen becherförmigen Isolator mit einem sie umschliessenden leitenden Zylinder mechanisch verbunden ist, wobei im Verbindungsbereich zwischen dem Isolator und dem leitenden Zylinder eine Abschirmelektrode vorgesehen ist. In derartigen Magnetrons wird bekanntlich ein Magnetfeld in axialer Richtung erzeugt und die Elektrode führt gegenüber dem Zylinder ein negatives Potential. Da die Verbindung zwischen dem leitenden Zylinder bzw. Elektrode und dem Isolator mit Hilfe eines ferromagnetischen Zwischenstücks bzw. einer ferromagnetischen Metallverbindung (Kovar) erfolgt, ergibt sich bei einer solchen Magnetfeldröhre ein magnetischer Streufluss zwischen den genannten Verbindungen. Geladene Teilchen, die aus den genannten Verbindungen austreten, werden infolge des Magnetfeldes auf einer spiralförmigen Bahn bewegt, die eine erhebliche, gegenüber der mittleren freien Weglänge der geladenen Teilchen nicht mehr vernachlässigbare Länge erreichen kann. Diese Ladungsträger können daher mit den Molekülen des in der Röhre noch enthaltenen Restgases kollidieren, was zu einer Glimmentladung führen kann. Die Abschirmelektrode, die grundsätzlich auch durch eine Abschirmelektrode im Bereich der Verbindung zwischen der Elektrode und dem Isolator ersetzt werden kann, muss nun so geformt sein, dass sie die Bahn der geladenen Teilchen zwischen den beiden Verbindungsbereichen schneidet und die geladenen Teilchen auf ihrer Bahn auf sie auftreffen können. Führt die Elektrode gegenüber dem leitenden Zylinder (jedoch) ein positives Potential, ist diese Formgebung hochspannungstechnisch ungünstig, weil aus der Abschirmelektrode emittierte Elektronen auf die Innenfläche des Isolators auftreffen können, wo sie Entladungsvorgänge auf der Oberfläche des Isolators hervorrufen.It should be mentioned at this point that a vacuum tube in the form of a magnetic field tube is already known from US-PS 4205250, with an electrode located in its vacuum space, which is mechanically connected via a cup-shaped insulator to a conductive cylinder surrounding it, in the connection area a shielding electrode is provided between the insulator and the conductive cylinder. As is known, such magnetrons generate a magnetic field in the axial direction and the electrode has a negative potential with respect to the cylinder. Since the connection between the conductive cylinder or electrode and the insulator takes place with the aid of a ferromagnetic intermediate piece or a ferromagnetic metal connection (Kovar), such a magnetic field tube results in a magnetic leakage flux between the connections mentioned. Charged particles that emerge from the compounds mentioned are moved as a result of the magnetic field on a spiral path, which can reach a considerable length, which is no longer negligible compared to the mean free path of the charged particles. These charge carriers can therefore collide with the molecules of the residual gas still contained in the tube, which can lead to a glow discharge. The shielding electrode, which can in principle also be replaced by a shielding electrode in the area of the connection between the electrode and the insulator, must now be shaped in such a way that it cuts the path of the charged particles between the two connection areas and the charged particles on their path on them can hit. If the electrode has a positive potential (however) with respect to the conductive cylinder, this shape is disadvantageous from a high-voltage point of view because electrons emitted from the shielding electrode can strike the inner surface of the insulator, where they cause discharge processes on the surface of the insulator.

Eine andere Weiterbildung der Erfindung sieht vor, dass der Isolator so geformt ist, dass zwischen ihm und dem leitenden Teil einzurAbschirmelektrode offener Hohlraum eingeschlossen wird. Hierbei ist der Bereich der Verbindungsstelle zwischen dem Isolator und dem leitenden Teil gegen Entladungsträger, die durch den Zwischenraum zwischen der Abschirmelektrode und dem Isolator hindurch in Richtung auf den elektrisch leitenden Teil laufen, weitgehend geschützt, so dass die Entladungsvorgänge besonders wirksam unterbunden werden können.Another development of the invention provides that the insulator is shaped in such a way that a cavity which is open between the shielding electrode and the conductive part is enclosed. Here, the area of the connection point between the insulator and the conductive part is largely protected against discharge carriers which run through the gap between the shielding electrode and the insulator in the direction of the electrically conductive part, so that the discharge processes can be prevented particularly effectively.

Die Erfindung wird nachstehend anhand eines in der Zeichnung dargestellten Ausführungsbeispiels näher erläutert. Es zeigen

  • Fig. 1 eine bekannte Röntgenröhre,
  • Fig. einen Teil einer solchen Röntgenröhre mit der erfindungsgemässen Ausgestaltung,
  • Fig. 3 und 4 andere Ausgestaltungen der Erfindung.
The invention is explained below with reference to an embodiment shown in the drawing. Show it
  • 1 shows a known X-ray tube,
  • FIG. 1 shows a part of such an X-ray tube with the configuration according to the invention,
  • 3 and 4 other embodiments of the invention.

Anhand der in Fig. 1 dargestellten bekannten Röntgenröhre sollen zunächst nochmals die der Erfindung zugrunde liegenden Probleme erläutert werden. Fig. 1 zeigt eine Röntgenröhre, deren Kolben 1 vollständig aus Metall besteht. Der Kolben 1 ist im wesentlichen rotationssymmetrisch aufgebaut. Die Anodenscheibe 2 weist eine abgeflachte Brennfleckbahn auf, der gegenüber die Kathode 3 angeordnet ist, die über einen Isolator 4 mit einem Metallzylinder 5 verbunden ist, der seinerseits mit dem in diesem Bereich eine Öffnung aufweisenden Kolben verbunden ist. Die Anode ist an zwei Stellen gehaltert. Am unteren Ende des Metallkolbens ist ein zur Rotationsachse konzentrischer Zapfen 6 vorgesehen, der ein Lager 7 trägt, das über einen Ring 8 mit dem zylinderförmigen Rotor 9 verbunden ist. Der Zapfen 6, das Lager 7 und der Ring 8 stellen eine leitende Verbindung zwischen dem Kolben 1 und dem Rotor 9 her, so dass mit dem Metallkolben auch der Rotor geerdet ist. Der Ring 8 und mit ihm der Rotor 9 ist über einen weiteren Ring 15 mit einem Isolator 11 verbunden, der auf einer die Anodenscheibe 2 tragenden Welle 12 befestigt ist.On the basis of the known x-ray tube shown in FIG. 1, the problems on which the invention is based will first be explained again. Fig. 1 shows an X-ray tube, the piston 1 is made entirely of metal. The piston 1 is essentially rotationally symmetrical. The anode disk 2 has a flattened focal spot path, which is arranged opposite the cathode 3, which is connected via an insulator 4 to a metal cylinder 5, which in turn is connected to the piston having an opening in this area. The anode is held in two places. At the lower end of the metal piston, a pin 6 is provided which is concentric with the axis of rotation and which carries a bearing 7 which is connected to the cylindrical rotor 9 via a ring 8. The pin 6, the bearing 7 and the ring 8 establish a conductive connection between the piston 1 and the rotor 9, so that the rotor is also grounded to the metal piston. The ring 8 and with it the rotor 9 is connected via a further ring 15 to an insulator 11 which is fastened on a shaft 12 carrying the anode disk 2.

Die Zufuhr der Hochspannung an die Anode erfolgt über ein weiteres Lager 13, das in einem mit dem Röhrenkolben 1 verbundenen Isolator 14 angebracht ist, der eine konusförmige Öffnung 16 zur Aufnahme eines Hochspannungssteckers aufweist. Das Kugellager 13 dient zur Lagerung der Welle 12. Die Hochspannung wird der Anodenscheibe 2 also über das Lager 13 und die Welle 12 zugeführt.The supply of the high voltage to the anode takes place via a further bearing 13, which is mounted in an insulator 14 connected to the tubular bulb 1, which has a conical opening 16 for receiving a high-voltage plug. The ball bearing 13 serves to support the shaft 12. The high voltage is thus supplied to the anode disk 2 via the bearing 13 and the shaft 12.

Solange die Röntgenröhre thermisch normal belastet wird, finden aufgrund der Form des Isolators 14 keine Entladungsvorgänge statt. Bei sehr starker thermischer Belastung jedoch können auch bei einer derartigen Röntgenröhre Entladungsvorgänge auftreten, insbesondere wenn der Isolator 14 und der Kolben 1 durch eine Hartlötverbindung miteinander verbunden sind. Der kritische Bereich ist dabei der Bereich 17, in dem der Kolben 1, der Isolator 14 und das Vakuum in der Röhre aneinander angrenzen. Dieser Bereich, der sich nicht, wie die Zeichnung vermuten lässt, auf einen Punkt beschränkt, sondern die Welle 12 konzentrisch umschliesst, ist dem elektrischen Feld zwischen dem Kolben 1 und der Welle 12 ausgesetzt. Er kann bei übermässiger thermischer Belastung Temperaturen von weit über 100°C annehmen.As long as the X-ray tube is subjected to normal thermal loads, no discharge processes take place due to the shape of the insulator 14. With very strong thermal stress, however, discharge processes can also occur with such an X-ray tube, in particular if the insulator 14 and the piston 1 are connected to one another by a brazed connection. The critical area is the area 17 in which the piston 1, the insulator 14 and the vacuum in the tube adjoin one another. This area, which, as the drawing suggests, cannot be limited to one point, but rather concentrically surrounds the shaft 12, is exposed to the electric field between the piston 1 and the shaft 12. If the thermal load is excessive, it can reach temperatures of well over 100 ° C.

Fig. 2 zeigt einen Teil des Metallkolbens mit dem Isolator 14 in teilweise aufgebrochener Darstellung in einem im Vergleich zu Fig. 1 vergrösserten Massstab mit der erfindungsgemässen Abschirmelektrode. Die ringförmige Abschirmelektrode 18 befindet sich in unmittelbarer Nähe des Endes des Isolators, in dem sich der kritische Bereich 17 befindet, in dem der Kolben 1, der Isolator und das Vakuum aneinandergrenzen. Die Abschirmelektrode besteht vorzugsweise aus Reineisen oder einem anderen Metall, z.B. CrNi-Stahl, und ist konzentrisch zur Welle 12 auf der Innenseite des Metallkolbens 1 angeschweisst.FIG. 2 shows a part of the metal piston with the insulator 14 in a partially broken-away representation on a larger scale compared to FIG. 1 with the shielding electrode according to the invention. The ring-shaped shielding electrode 18 is located in the immediate vicinity of the end of the insulator, in which the critical region 17 is located, in which the piston 1, the insulator and the vacuum adjoin one another. The shielding electrode is preferably made of pure iron or another metal, e.g. CrNi steel, and is welded concentrically to the shaft 12 on the inside of the metal piston 1.

Sowohl die Abschirmelektrode als auch der Isolator sind so geformt, dass sie mit dem Kolben 1 jeweils einen nutenförmigen Hohlraum 21 bzw. 20 bilden, der zum Isolator bzw. zur Abschirmelektrode hin offen ist. Durch diese Gestaltung wird einerseits die Feldstärke in dem kritischen Bereich herabgesetzt und andererseits können die durch den Spalt zwischen der Abschirmelektrode 18 und dem Isolator 14 hindurchtretenden Ladungsträger nicht unmittelbar diesen kritischen Bereich treffen.Both the shielding electrode and the insulator are shaped such that they each form a groove-shaped cavity 21 or 20 with the piston 1, which is open towards the insulator or the shielding electrode. This design on the one hand reduces the field strength in the critical area and on the other hand the charge carriers passing through the gap between the shielding electrode 18 and the insulator 14 cannot hit this critical area directly.

Der Spalt zwischen den einander zugewandten Enden des Isolators 14 und der Abschirmelektrode 18 beträgt etwa 1 mm. Er sollte aber 3 mm nicht überschreiten. Ist er jedoch wesentlich kleiner als 0,5 mm, dann ergeben sich in diesem Spalt sehr hohe Feldstärken, die zur Feldemission auf der Oberfläche der Abschirmelektrode 18 führen können. Ausserdem lässt sich die Abschirmelektrode dann schlecht konditionieren. Ist er wesentlich grösser als 3 mm, dann wird das elektrische Feld in dem kritischen Bereich zwischen Metallkolben 1, Isolator 14 und Vakuum kaum durch die Abschirmelektrode 18 herabgesetzt.The gap between the mutually facing ends of the insulator 14 and the shielding electrode 18 is approximately 1 mm. However, it should not exceed 3 mm. However, if it is significantly smaller than 0.5 mm, then very high field strengths result in this gap, which can lead to field emission on the surface of the shielding electrode 18. In addition, the shielding electrode can then be poorly conditioned. If it is significantly larger than 3 mm, then the electric field in the critical area between metal piston 1, insulator 14 and vacuum is hardly reduced by the shielding electrode 18.

Zweckmässigerweise wird die Abschirmelektrode z.B. durch Elektropolieren so behandelt, dass sich auf ihrer Oberfläche kaum Emissionszentren befinden. Um zu verhindern, dass gleichwohl noch aus ihrer Oberfläche austretende Elektronen auf die der Welle 12 zugewandten Fläche des lsolators treffen können und auf dieser zur Welle 12 bzw. dem damit verbundenen Kugellager 13 (Fig. 1) laufen können, wodurch Entladungsvorgänge ausgelöst werden könnten, sollte die Elektrode 18 so angeordnet sein, dass aus ihr emittierte Elektronen direkt zur Welle 12 laufen und den Isolator nicht erreichen können. Zu diesem Zweck ist die Abschirmelektrode zweckmässigerweise zurückgesetzt angeordnet, d.h. ihr Innendurchmesser ist so bemessen, dass die kegelstumpfförmige, sich zur Abschirmelektrode hin erweiternde Innenmantelfläche des Isolators 14 bzw. deren durch Linien 19 angedeutete Verlängerung die Abschirmelektrode 18 nicht schneiden.The shielding electrode is expediently e.g. treated by electropolishing so that there are hardly any emission centers on its surface. In order to prevent electrons that still emerge from their surface from striking the surface of the insulator facing the shaft 12 and from running to the shaft 12 or the associated ball bearing 13 (FIG. 1), which could trigger discharge processes, the electrode 18 should be arranged so that electrons emitted from it run directly to the shaft 12 and cannot reach the insulator. For this purpose, the shielding electrode is expediently arranged in a reset manner, i.e. its inner diameter is dimensioned such that the frustoconical inner jacket surface of the insulator 14, which extends towards the shielding electrode or its extension, indicated by lines 19, does not intersect the shielding electrode 18.

Eine andere Ausführungsform der Erfindung ist in Fig. 3 dargestellt, die einen Ausschnitt aus einer erfindungsgemässen Röntgenröhre zeigt. Die einander zugewandten Stirnflächen 22 bzw. 23 des Isolators 14 und der Abschirmelektrode 18 sind dabei näherungsweise eben und verlaufen ungefähr senkrecht zur Wand des Metallkolbens 1. Dadurch wird zwar die Feldstärke in der kritischen Zone zwischen dem Kolben, dem Isolator 14 und dem Vakuum herabgesetzt, doch können durch den Spalt hindurchtretende Ladungsträger diese Zone unmittelbar erreichen. Diese Ausführungsform ist daher nicht ganz so wirksam wie die in Fig. 2 dargestellte.Another embodiment of the invention is shown in FIG. 3, which shows a section of an X-ray tube according to the invention. The mutually facing end faces 22 and 23 of the insulator 14 and the shielding electrode 18 are approximately flat and run approximately perpendicular to the wall of the metal piston 1. This does indeed reduce the field strength in the critical zone between the piston, the insulator 14 and the vacuum, however, charge carriers passing through the gap can reach this zone directly. This embodiment is therefore not quite as effective as that shown in FIG. 2.

Eine weitere Ausführungsform istschliesslich in Fig. 4 dargestellt. Die Abschirmelektrode 18 ist dabei ähnlich geformt wie in Fig.2, d.h. sie schliesst mit der Wand des Kolbens 1 einen nutenförmigen, umlaufenden und zum Isolator 14 hin offenen Hohlraum 21 ein, in den ein vergleichsweise dünnes Ende des Isolators 14 hineinragt.Another embodiment is finally shown in FIG. 4. The shielding electrode 18 is shaped similarly to that in FIG. it encloses with the wall of the piston 1 a groove-shaped, circumferential cavity 21 which is open towards the insulator 14 and into which a comparatively thin end of the insulator 14 projects.

Obwohl die Erfindung vorstehend in Verbindung mit einem feststehenden Isolator erläutert wurde, ist sie grundsätzlich auch bei einem rotierenden Isolator anwendbar. Wenn beispielsweise in Fig. 1 der geerdete Metallring 15 so lang wäre, dass sich ein Bereich bzw. eine Zone ergäbe, in der der Vakuumraum, der Metallring 15 und der Isolator 11 aneinander angrenzen und in die das zwischen dem Metallring 15 und der Welle 12 wirksame elektrische Feld eingreifen würde, könnte die Erfindung auch dabei entsprechend angewandt werden.Although the invention has been explained above in connection with a fixed insulator, it can in principle also be used with a rotating insulator. If, for example in FIG. 1, the grounded metal ring 15 were so long that there would be an area or a zone in which the vacuum space, the metal ring 15 and the insulator 11 adjoin one another and into which that between the metal ring 15 and the shaft 12 would intervene effective electrical field, the invention could also be applied accordingly.

In der Zeichnung ist der Isolator so geformt, dass die im Betriebszustand auftreffenden Elektronen zumindest auf einem wesentlichen Teil seiner Oberfläche ein elektrisches Feld vorfinden, das sie von der Isolatoroberfläche weg bewegt, weil der kegelstumpfförmige Innenmantel des Isolators sich in Achsrichtung gesehen von dem Verbindungsbereich mit der Elektrode aus erweitert.In the drawing, the insulator is shaped in such a way that the electrons striking in the operating state find an electric field at least on a substantial part of its surface, which moves it away from the insulator surface, because the truncated cone-shaped inner jacket of the insulator extends in the axial direction from the connection area with the Electrode expanded.

Anstelle dieser Isolatorform ist die Erfindung jedoch auch bei einer Isolatoranordnung anwendbar, die mit einer konzentrischen Mulde versehen ist und einen von der Mulde umschlossenen, die Elektrode tragenden Isolatorteil aufweist sowie einen äusseren Isolatorteil, der die Mulde umschliesst und mit dem leitenden Teil (dem Röhrenkolben oder dem Rotor) verbunden ist.Instead of this form of insulator, however, the invention can also be applied to an insulator arrangement which is provided with a concentric trough and has an insulator part which is enclosed by the trough and carries the electrode, and an outer insulator part which surrounds the trough and with the conductive part (the tubular bulb or the rotor) is connected.

Die Erfindung beschränkt sich auch nicht auf Drehanoden-Röntgenröhren. Sie kann vielmehr auch bei anderen Röntgenröhren sowie bei anderen Hochspannungs-Vakuumröhren (z.B. Neutronenröhren) angewandt werden.The invention is also not limited to rotating anode X-ray tubes. Rather, it can also be used with other X-ray tubes and with other high-voltage vacuum tubes (e.g. neutron tubes).

Claims (6)

1. A high-voltage vacuum tube, specifically an X-ray tube, which comprises an electrode disposed in its vacuum space, which electrode carries a positive high voltage relative to an electrically conductive part by which it is at least partly enclosed, the electrode or a part connected to the electrode being connected to the conductive part via an insulator, characterized in that at the location (17) of the connection between the insulator (14) and the conductive part (1) a shielding electrode (18) carrying the potential of the conductive part (1) is arranged, which electrode forms a gap- like or groove-like space in conjunction with the neighbouring insulator (14) and comprises a surface area which is remote from the neighbouring inner wall of the conductive part (1) so as to reduce the electric field strength at the location (17) of the connection, said surface area of the shielding electrode (18) being shaped so that the electrons emitted thereby for the most part cannot impinge on the inner surface of the insulator (14).
2. A high-voltage vacuum tube as claimed in Claim 1, characterized in that the shielding electrode (18) recedes from the generated surface (19) defined by the inner surface of the insulator (14), so that it does not intersect the extension (19) of the conical inner surface of the insulator (14).
3. A high-voltage vacuum tube as claimed in any one of the preceding Claims, characterized in that the shielding electrode (18) is constructed so that between this electrode and the conductive part (1) a cavity (21) is enclosed, which cavity is open towards the insulator (Fig. 2).
4. A high-voltage vacuum tube as claimed in any one of the preceding Claims, characterized in that the insulator is constructed so that between this insulator and the conductive part a cavity (20) is enclosed, which cavity is open towards the shielding electrode (Fig. 2).
5. A high-voltage vacuum tube as claimed in any one of the preceding Claims, characterized in that the end surface (22) of the insulator which faces the shielding electrode is flat and extends substantially perpendicularly to the wall (Fig. 3).
6. A high-voltage vacuum tube as claimed in any one of the preceding Claims, characterized in that the end surface (23) of the shielding electrode which faces the insulator is flat and extends substantially perpendicularly to the surface of the conductive part (Fig. 3).
EP82200452A 1981-04-23 1982-04-14 High tension vacuum tube, particularly x ray tube Expired EP0063840B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19813116169 DE3116169A1 (en) 1981-04-23 1981-04-23 HIGH VOLTAGE VACUUM TUBES, ESPECIALLY X-RAY TUBES
DE3116169 1981-04-23

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EP0063840A1 EP0063840A1 (en) 1982-11-03
EP0063840B1 true EP0063840B1 (en) 1985-10-16

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EP82200452A Expired EP0063840B1 (en) 1981-04-23 1982-04-14 High tension vacuum tube, particularly x ray tube

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US (1) US4499592A (en)
EP (1) EP0063840B1 (en)
JP (1) JPS57182952A (en)
CA (1) CA1184231A (en)
DE (2) DE3116169A1 (en)
IL (1) IL65554A (en)

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Also Published As

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DE3116169A1 (en) 1982-11-11
CA1184231A (en) 1985-03-19
US4499592A (en) 1985-02-12
EP0063840A1 (en) 1982-11-03
IL65554A (en) 1985-04-30
JPS57182952A (en) 1982-11-11
JPH0355933B2 (en) 1991-08-26
IL65554A0 (en) 1982-07-30
DE3266898D1 (en) 1985-11-21

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