EP3053182B1 - Radiation generation device - Google Patents

Radiation generation device Download PDF

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Publication number
EP3053182B1
EP3053182B1 EP14772094.0A EP14772094A EP3053182B1 EP 3053182 B1 EP3053182 B1 EP 3053182B1 EP 14772094 A EP14772094 A EP 14772094A EP 3053182 B1 EP3053182 B1 EP 3053182B1
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EP
European Patent Office
Prior art keywords
cathode
emission surface
generating apparatus
radiation generating
central axis
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EP14772094.0A
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German (de)
French (fr)
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EP3053182A1 (en
Inventor
Oliver Heid
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Siemens AG
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Siemens AG
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H01J3/027—Construction of the gun or parts thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/14—Arrangements for focusing or reflecting ray or beam
    • H01J3/18—Electrostatic lenses
    • 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
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H01J35/147—Spot size control

Definitions

  • the present invention relates to a radiation generator according to claim 1.
  • An electron gun generally has a cathode for emitting free electrons, which are subsequently accelerated by an electron optical system.
  • electrostatic lenses or magnetic fields are used.
  • the minimum achievable focus size is limited in electron beams high current density by the mutual repulsion of the electrons within the beam.
  • pamphlet US 2007/0278928 A1 describes an electron source for low energy electrons.
  • pamphlet US 3980919 describes an electron source for emitting an electron beam of rectangular cross-section, which comprises a cathode with a planar, rectangular emission surface.
  • pamphlet JP H05174761 A describes an electron source with a cathode, which also has a rectangular, planar emission surface.
  • pamphlet US 2842703 describes an electron source with a concave cathode in the form of a circular disk.
  • pamphlet DE 2334106 describes a device for welding the end faces of tubular bodies by means of an electron beam generated by a ring cathode.
  • pamphlet DE 1589006 describes an electrode system for generating an electron beam with a ring-shaped cathode for material processing.
  • pamphlet WO 2015/05897 A1 describes a device for generating accelerated electrons for the chemical material modification or disinfection of surfaces.
  • DE 10 2009 038 687 A1 discloses a beam generator for generating X-radiation.
  • the object of the present invention is to provide an improved radiation generating system. This object is achieved by a radiation generating system having the features of claim 1. Preferred developments are specified in the dependent claims.
  • the emission surface has a width in the azimuthal direction and a height oriented perpendicular to the width, the width being at least ten times as great as the height. Width and height are each defined along the emission surface, wherein the azimuthal or width direction designates the direction in which the emission surface has the curvature about the central axis.
  • an electron flat-beam with a large width-to-thickness ratio can be generated.
  • the thickness of the beam is defined perpendicular to the width direction and perpendicular to a beam direction. Since the flat electron beam can change its direction during acceleration, the beam direction always refers to the local mean direction of movement of the electrons.
  • Such a flat jet can be advantageously well focused in the thickness direction, which allows the generation of a very fine focal line.
  • the accelerating device is designed to deflect the electrons in the thickness direction. This allows the electron gun a beam guide that is not limited to one plane.
  • the acceleration device is additionally designed to to focus the electron flat beam in the thickness direction. This advantageously allows the generation of a focused flat electron beam.
  • the width of the emission surface is at least one hundred times, preferably at least one thousand times greater than its height.
  • a larger width leads to a reduction in the current density and thus the space charge forces at the cathode. Since space charge forces, in particular in the areas in which the flat electron beam is slow, have a great influence on the beam quality, an improvement in the emittance of the beam can advantageously be achieved by a lower space charge density at the cathode.
  • the emission surface of the cathode is formed as a closed ring.
  • the cathode has no edge surfaces in the width direction whose stray fields could cause a deflection of the electron flat beam.
  • the space charge forces compensate for a single electron in the width direction, so that a radial beam guidance is much easier.
  • a beam direction in the target area does not lead to the emission area of the cathode.
  • a beam direction at the location of the cathode is not perpendicular to the central axis.
  • a beam direction in the target area is not perpendicular to the central axis. In this way, it can likewise be avoided that electrons which leave the cathode along the relevant beam direction and / or pass through the target area impinge on an opposite part of the emission surface.
  • an edge surface of an electrode of the acceleration device is formed as a segment of a surface of revolution, wherein the axis of rotation of the surface is oriented parallel to the central axis.
  • the rotational surface segment forming an edge surface of an electrode comprises a rotation angle of three hundred and sixty degrees. This allows a compact and simple design of the accelerating device, in particular, but not exclusively, when all the edge surfaces facing the electrons of the accelerating device are formed in this way. In addition, stray fields at the azimuthally limiting surfaces of rotation are avoided, which facilitates beam guidance in the radial direction.
  • An annular formation of the accelerating device also makes it possible to focus the flat electron beam in the width direction alone by a radial beam guidance on the target area. It thus eliminates otherwise possibly necessary elements that cause a focus in the width direction, which simplifies the structure of the overall system.
  • a small current density and a reduced space charge effect are realized by an annular configuration in a particularly simple manner at the location of the cathode, while at the same time the current density of the electrons in the target area can be high.
  • the acceleration device has a device for generating a magnetic field. This advantageously allows a magnetic deflection of the electrons. Magnetic field-guided beam guidance and focusing makes it possible to realize electron-optical elements with small aberrations, which can further reduce the achievable focus size.
  • the magnetic field is rotationally symmetrical with respect to an axis which is aligned parallel to the central axis.
  • a radiation generating system has an electron gun of the aforementioned type, in whose target area a target structure is arranged.
  • the good focussability of the electron flat-beam generated by the electron gun allows a high current density on the target structure and thus, for example, a high intensity of the generated radiation.
  • the target structure is formed as an X-ray target. As a result, a particularly compact x-ray source of high intensity can be realized.
  • the accelerator device of the electron gun is designed to accelerate the electrons to an energy of at least 25 keV, preferably to an energy of at least 100 keV. This enables a particularly efficient generation of short-wave X-ray light.
  • FIG. 1 the sectional view of an electron gun 1 is shown schematically.
  • the electron gun 1 makes it possible to generate a flat electron beam and to focus it both in the thickness and in the width direction. While focusing in the thickness direction is realized by electron-optical elements, focusing in the width direction is achieved by a radial beam guidance.
  • all elements of this embodiment are arranged rotationally symmetrical about a central axis 20. In addition to the rotational symmetry, the entire structure has a mirror symmetry with respect to a centrally arranged beam plane 11.
  • the illustrated electron gun 1 comprises an annular cathode 100 and an accelerator 200.
  • the cathode 100 has an emitting surface 110 which is located on the inner surface of the cathode 100 and oriented in the direction of the central axis 20.
  • the accelerator 200 includes a likewise annular cathode electrode 230 surrounding the outside of the cathode 100, and a lower lens electrode 210 and an upper lens electrode 215 disposed between the cathode 100 and the central axis 20 are arranged.
  • the accelerator 200 includes a lower anode member 220 and an upper anode member 225.
  • the cathode 100 is designed as a rotation body with a rotation axis 101, and the elements of the acceleration device 200 as a rotation body with a common rotation axis 201.
  • the axes of rotation 101, 201 of the cathode 100 and accelerator 200 coincide with the center axis 20.
  • embodiments are also possible in which two or all three axes do not lie on top of each other but are only arranged parallel to one another.
  • the individual elements 210, 215, 220, 225, 230 of the acceleration device 200 may have differently arranged axes of rotation.
  • the cathode 100 and the cathode electrode 230 form an outer ring around the central axis 20.
  • the ring-shaped lens electrodes 210, 215, which are likewise annular, are arranged concentrically in the interior of this ring.
  • the lower lens electrode 210 and the upper lens electrode 215 are symmetrical to each other on one side of the beam plane 11. Electrons emitted from the emission surface 110 of the cathode 100 move radially along the beam plane 11 in the space between the lens electrodes 210, 215 inside to a target area 30, which is located in the center of the electron gun 11 on the central axis 20.
  • the lower anode element 220 and the upper anode element 225 are arranged, both of which are conical. Like the lens electrodes 210, 215, they lie symmetrically on opposite sides of the beam plane 11, so that accelerated electrons can traverse the resulting gap along the beam plane 11.
  • FIG. 2 a perspective schematic representation of a segment of the electron gun 1. Due to the rotationally symmetrical design of the lens electrodes 210, 215, the surfaces of these electrodes form surfaces of revolution. In the illustrated embodiment of the electron gun 1, the electrons move in particular along an edge surface 211 of the lower lens electrode 210 and an edge surface 216 of the upper lens electrode 215.
  • the emission surface 110 of the cathode 100 has a width 120 which is at least ten times greater than a height 130 which is measured perpendicular to the width 120 along the emission surface. Width and height are each defined along the emission surface 110, with an azimuthal or width direction 125 designating the direction in which the emission surface 110 has the curvature about the central axis 20. In general, the curvature of the emission surface 110 along the width direction 125 need not be constant. In addition to a curvature caused by the ring shape along the width direction 125, the emission surface 110 in the illustrated embodiment also has a curvature along its height 120.
  • the emission surface 110 comprises the region of the surface of the cathode 100, from which electrons are guided to the target region 30 due to the configuration of the electron gun 1.
  • the emission surface 110 can also be defined by a diaphragm which is arranged between the cathode 100 and the target region 30 and which delimits the emitted beam.
  • FIG. 3 shows a further illustration of the electron gun 1, in addition also exemplified a generated flat electron beam 10 is shown in cross section.
  • the cathode 100 and the lower and upper lens electrodes 210, 215 are arranged so that emitted electrons Each location of the emission surface 110 can be accelerated in a respective radial direction 140 toward the target area.
  • the cathode 100 and the lens electrodes 210, 215 are additionally formed so that a negative voltage with respect to the cathode electrodes 210, 215 can be applied to the cathode 100.
  • a disk-shaped flat electron beam 10 is formed, which is arranged symmetrically about the beam plane 11.
  • Electrons which exit the region between the lens electrodes 210, 215 in a focusing region 250 are then further accelerated to the desired final velocity in the target region 30.
  • an electrical voltage can also be applied between the anode elements 220, 225 and the lens electrodes 210, 215.
  • the inner edge surfaces of the lens electrodes 210, 215 and the edge surfaces of the anode elements 220, 225 are additionally formed such that when voltage is applied in a focusing region 250 an electric field is formed, in which the flat electron beam 10 in a thickness direction 150, which in the shown Embodiment is oriented at each location parallel to the central axis 20, is focused.
  • An exemplary voltage assignment to obtain the sketched beam path at a beam energy of 25 keV to 200 keV is, based on the cathode potential, a voltage of 25 kV to 200 kV on the anode elements 220, 225.
  • the lens electrodes 210, 215 are then with about one fifth of the anode voltage is applied, that is about 5 kV to 40 kV.
  • the anode elements 220, 225 are applied with 50 kV and the lens electrodes 210, 215 with 10 kV, particularly preferably with 100 kV or 20 kV.
  • a beam energy of 25 keV to 200 keV represents a sensible energy range for the generation of X-ray light, in which an X-ray spectrum suitable for medical applications, for example, is generated in conventional X-ray targets.
  • the flat electron beam 10 In order to focus the flat electron beam 10 on the target area 30, two different methods are used in the width direction 125 and the thickness direction 150.
  • the flat electron beam In the thickness direction 150, the flat electron beam is focused by an electrostatic lens.
  • a beam guidance directed radially inward on the target area 30 is used, whereby no deflection of the electrons in the width direction 125 is required.
  • the in the FIGS. 1 to 3 shown rotationally symmetrical design of the electron gun 1 has the advantage that compensate for the space charge forces generated in the width direction 125 by the mutual repulsion of the electrons of the flat electron beam 10.
  • the flat electron beam 10 can be focused very finely not only in the thickness direction 150 but also in the width direction 125.
  • the remaining radial component of the space charge has a negligible effect on the achievable focus size.
  • the fields generated by the cathode 100 and the accelerating device 200 in the width direction 125 are also homogeneous and depend only on the radial distance of the electrons from the central axis 20. Therefore, no edge fields occur in the width direction 125, which could lead to a deflection of the beam.
  • electron gun 1 allows a large emission area 110 in the edge region of the electron gun 1 and thus a low electron density at the points where the electrons are still slow. This has a beneficial effect on the beam quality, since space charges affect them especially in those areas where the resulting forces can accelerate the electrons to velocities comparable to the longitudinal velocity of the beam.
  • a critical density for space charge effects is achieved by the flat electron beam 10 only in the vicinity of the target area 30, where such a high density is desired and the electrons are so fast that space charge forces only play a minor role.
  • an isotropic beam shape in the target region 30 can be achieved by the illustrated beam guidance in the radial direction 140.
  • the flat beam shape also makes it possible to achieve small foci in the target area 30 with a moderate electron optical reduction. As a result, the requirements for the imaging quality of the electron lens, which is formed by the electric field in the focusing region 250, decrease. In particular, it is possible to use purely electrostatic lenses with relatively large spherical aberrations and it can be dispensed with elaborate lens shapes, such as magnetic immersion lenses.
  • the advantages achieved by a large width-to-height ratio of the emitting surface 110 are particularly pronounced when the width 120 is at least one hundred times, better yet at least one thousand times greater than the height 130.
  • the width 120 is at least one hundred times, better yet at least one thousand times greater than the height 130.
  • a perveance of 2 * 10 ⁇ -6 A / V ⁇ (3/2) gives a minimum primary focus of about 0.6 mm.
  • an electron optical reduction of one to twelve is required.
  • an emission surface of the same size can be realized by a 300 mm wide and 100 ⁇ m high annular strip.
  • the required reduction ratio in the thickness direction 150 is then only one to two and can be achieved with electrostatic lenses.
  • the illustrated closed arrangement of the emission area 110 around the target area 30 and the configuration of the anode elements 220, 225 as cones in the center are just one possible variant.
  • a focusing of the electron flat beam 10 can then be achieved by a suitable shaping of the electrode surfaces.
  • the accelerator 200 may consist of more electrodes than the cathode electrode 230, the lens electrodes 210, 215 and the anode elements 220, 225.
  • the accelerator 200 may consist of more electrodes than the cathode electrode 230, the lens electrodes 210, 215 and the anode elements 220, 225.
  • a separate design of electrodes that pull the electrons from the cathode and electrodes that focus the flat electron beam 10 is possible.
  • these could also be combined with the cathode 100 into a single element.
  • the electrode surfaces facing the electron flat beam 10 for example a surface 211 of the lower lens electrode 210 and / or a surface 216 of the upper lens electrode 215, need not necessarily be designed as rotation surfaces in order to achieve the desired beam guidance in the radial direction 140.
  • further elements such as radial grooves or webs to the electrodes in order to allow additional beam shaping.
  • additional elements and diaphragms are integrated into the electron gun 1. critical with all these modifications, it is merely that the electric field which results when voltage is applied to the electrodes, further enables beam guidance in the primarily radial direction 140.
  • both the cathode 10, the cathode electrode 230, and the lens electrodes 210, 215 and the anode elements 220, 225 are formed as a rotational body.
  • a segmental configuration in which in particular the emission surface of the cathode 110 and / or one or more edge surfaces of the lower lens electrode 210 and / or one or more edge surfaces of the upper lens electrode 216 are formed only as segments of a rotation surface.
  • the segments include instead of in the FIGS. 1 and 3 three hundred and sixty degrees, for example, only ninety or one hundred and eighty degrees.
  • a rotation axis 219 of the corresponding edge surfaces is oriented parallel to the center axis 20 and particularly preferably coincides therewith.
  • This embodiment would correspond to the schematic representation in FIG. 2 , wherein the electrodes consist exclusively of the illustrated segments.
  • additional edge electrodes could be provided to minimize the influence of stray fields at the segment edges.
  • an embodiment of the cathode 100, the cathode electrode 230, the lens electrodes 210, 215 and the anode elements 220, 225 as segments of a rotating body is not required to produce according to the invention, a flat electron beam, in which by a radially convergent beam guide Focusing in the width direction 125 is supported.
  • a curved version of the emission surface 110 with a not necessarily constant curvature and a correspondingly large ratio of width 120 and height 130 of the emission surface 110 are sufficient.
  • the accelerator 200 may include, in addition to the lens electrodes 210, 215, means for generating a magnetic field 240, 245 consisting of, for example, a lower magnetic field generating element 240 and an upper magnetic field generating element 245 shown in FIG FIG. 1 are shown.
  • a magnetic field 240, 245 consisting of, for example, a lower magnetic field generating element 240 and an upper magnetic field generating element 245 shown in FIG FIG. 1 are shown.
  • the device for generating a magnetic field 240, 245 generates a rotationally symmetrical magnetic field, with a rotation axis 242, which coincides with the central axis 20. As a result, the symmetry of the structure is not disturbed.
  • the described radial beam guidance can also include a deflection of the electron flat jet 10 in the thickness direction 150 so that it no longer runs everywhere in the same plane.
  • a beam guidance can be achieved, for example, by a suitable configuration of the lens electrodes 210, 215 of the acceleration device 200.
  • a simultaneous deflection and focusing of the beam is possible.
  • FIG. 4 For example, with an electron gun 3, a modified embodiment of the electron gun 1 in which the lower lens electrode 210 and the upper lens electrode 215 have been replaced by a lower deflection electrode 260 and an upper deflection electrode 265, respectively. These are no longer mirror-symmetrically shaped with respect to a beam plane 12 in the cathode region, so that an electron flat beam 15 in the exit region 251 at the end of the deflection electrodes 260, 265 is deflected parallel to the central axis 20.
  • the illustrated beam guidance is characterized, inter alia, by the fact that a beam direction 14 in the target area 30 does not point to the emission area 110 of the cathode 100. This avoids that emitted electrons can again impinge on a part of the emission surface 110 on the side opposite to their emission site and there contaminate the emission surface 110, for example by electron beam-induced adsorption.
  • the same goal can also be achieved if the beam direction 14 in the target region 30 is not perpendicular to the central axis 20, but the beam guide otherwise contains no deflection in the thickness direction 150. In this case, a flat electron beam is generated, which forms approximately a cone sheath.
  • a renewed impact of the electrons on the emission region 110 can also be prevented by a beam direction 13 in the region of the cathode 100 not being perpendicular to the central axis 20.
  • the electrons may then be deflected, for example, by suitable shaping and applying voltage to the cathode electrode 230 and / or the lens electrodes 210, 215 and / or additional electrodes to a beam plane perpendicular to the central axis 20, and then further radially inward be accelerated.
  • the electron guns 1 and 3 are designed as part of a radiation generating installation 2 which additionally comprises a target structure 31 arranged in the target area 30.
  • this is a target for generating X-ray radiation.
  • Possible materials for such an X-ray target are, for example, tungsten, rhenium-tungsten alloys, molybdenum, copper or cobalt.
  • the target structure 31 may, for example, have a cylindrical shape and be arranged symmetrically about the central axis 20.

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Description

Die vorliegende Erfindung betrifft eine Strahlungserzeugungsanlage gemäß Anspruch 1. Eine Elektronenkanone weist im Allgemeinen eine Kathode zur Emission freier Elektronen auf, welche anschließend durch ein elektronenoptisches System beschleunigt werden. Zusätzlich können Vorrichtungen vorhanden sein, die die Elektronen zu einem gerichteten Strahl bündeln und auf einen Zielbereich fokussieren. Hierzu werden zum Beispiel elektrostatische Linsen oder auch Magnetfelder eingesetzt. Die dabei minimal erreichbare Fokusgröße ist bei Elektronenstrahlen hoher Stromdichte durch die gegenseitige Abstoßung der Elektronen innerhalb des Strahls begrenzt.The present invention relates to a radiation generator according to claim 1. An electron gun generally has a cathode for emitting free electrons, which are subsequently accelerated by an electron optical system. In addition, there may be devices that focus the electrons into a directional beam and focus on a target area. For this purpose, for example, electrostatic lenses or magnetic fields are used. The minimum achievable focus size is limited in electron beams high current density by the mutual repulsion of the electrons within the beam.

Druckschrift US 2007/0278928 A1 beschreibt eine Elektronenquelle für niederenergetische Elektronen. Druckschrift US 3980919 beschreibt eine Elektronenquelle zur Emission eines Elektronenstrahls mit rechteckigem Querschnitt, welche eine Kathode mit planer, rechteckiger Emissionsfläche umfasst. Druckschrift JP H05174761 A beschreibt eine Elektronenquelle mit einer Kathode, die ebenfalls eine rechteckige, plane Emissionsfläche aufweist. Druckschrift US 2842703 beschreibt eine Elektronenquelle mit einer konkaven Kathode in Form einer Kreisscheibe.pamphlet US 2007/0278928 A1 describes an electron source for low energy electrons. pamphlet US 3980919 describes an electron source for emitting an electron beam of rectangular cross-section, which comprises a cathode with a planar, rectangular emission surface. pamphlet JP H05174761 A describes an electron source with a cathode, which also has a rectangular, planar emission surface. pamphlet US 2842703 describes an electron source with a concave cathode in the form of a circular disk.

Druckschrift DE 2334106 beschreibt eine Vorrichtung zum Verschweißen der Stirnflächen rohrförmiger Körper mittels eines von einer Ringkathode erzeugten Elektronenstrahls. Druckschrift DE 1589006 beschreibt ein Elektrodensystem zur Erzeugung eines Elektronenstrahls mit einer ringförmig ausgebildeten Kathode für die Materialbearbeitung. Druckschrift WO 2015/05897 A1 beschreibt eine Vorrichtung zum Erzeugen beschleunigter Elektronen für die chemische Materialmodifikation oder Desinfektion von Oberflächen. DE 10 2009 038 687 A1 offenbart eine Strahlerzeugungsanlage zur Erzeugung von Röntgenstrahlung.pamphlet DE 2334106 describes a device for welding the end faces of tubular bodies by means of an electron beam generated by a ring cathode. pamphlet DE 1589006 describes an electrode system for generating an electron beam with a ring-shaped cathode for material processing. pamphlet WO 2015/05897 A1 describes a device for generating accelerated electrons for the chemical material modification or disinfection of surfaces. DE 10 2009 038 687 A1 discloses a beam generator for generating X-radiation.

Aufgabe der vorliegenden Erfindung ist es, eine verbesserte Strahlungserzeugungsanlage bereitzustellen. Diese Aufgabe wird durch eine Strahlungserzeugungsanlage mit den Merkmalen des Anspruchs 1 gelöst. Bevorzugte Weiterbildungen sind in den abhängigen Ansprüchen angegeben.The object of the present invention is to provide an improved radiation generating system. This object is achieved by a radiation generating system having the features of claim 1. Preferred developments are specified in the dependent claims.

Gemäß der Erfindung umfasst eine Elektronenkanone einer Strahlerzeugungsanlage gemäss Anspruch 1 zur Erzeugung eines Elektronen-Flachstrahls eine Kathode mit einer um eine Zentralachse gekrümmten Emissionsfläche, die dazu ausgebildet ist, Elektronen zu emittieren, sowie eine Beschleunigungsvorrichtung zur radialen Beschleunigung der Elektronen in Richtung eines Zielbereich an der Zentralachse. Des Weiteren weist die Emissionsfläche eine Breite in azimutaler Richtung und eine senkrecht zur Breite orientierte Höhe auf, wobei die Breite mindestens zehnmal so groß wie die Höhe ist. Breite und Höhe sind jeweils entlang der Emissionsfläche definiert, wobei die azimutale oder Breitenrichtung die Richtung bezeichnet, in der die Emissionsfläche die Krümmung um die Zentralachse aufweist.According to the invention, an electron gun of a beam generating system according to claim 1 for generating a flat electron beam comprises a cathode having an emission surface curved about a central axis, which is adapted to emit electrons, and an accelerating device for radially accelerating the electrons toward a target region on the central axis. Furthermore, the emission surface has a width in the azimuthal direction and a height oriented perpendicular to the width, the width being at least ten times as great as the height. Width and height are each defined along the emission surface, wherein the azimuthal or width direction designates the direction in which the emission surface has the curvature about the central axis.

Durch die erfindungsgemäße Ausgestaltung der Emissionsfläche der Kathode kann ein Elektronen-Flachstrahl mit einem großen Breiten-zu-Dicken-Verhältnis erzeugt werden. Die Dicke des Strahls wird dabei senkrecht zur Breitenrichtung und senkrecht zu einer Strahlrichtung definiert. Da der Elektronen-Flachstrahl seine Richtung während der Beschleunigung ändern kann, wird mit der Strahlrichtung immer auf die lokale mittlere Bewegungsrichtung der Elektronen Bezug genommen. Ein solcher Flachstrahl lässt sich vorteilhafterweise in Dickenrichtung gut fokussieren, was die Erzeugung einer sehr feinen Brennlinie ermöglicht.The inventive design of the emission surface of the cathode, an electron flat-beam with a large width-to-thickness ratio can be generated. The thickness of the beam is defined perpendicular to the width direction and perpendicular to a beam direction. Since the flat electron beam can change its direction during acceleration, the beam direction always refers to the local mean direction of movement of the electrons. Such a flat jet can be advantageously well focused in the thickness direction, which allows the generation of a very fine focal line.

Zusätzlich ist bei Flachstrahlen zur Fokussierung in Dickenrichtung eine geringere elektronenoptische Verkleinerung als bei Rundstrahlen gleicher Querschnittsfläche notwendig, wodurch die Anforderungen an die elektronenoptische Qualität einer Linse zur Fokussierung in dieser Richtung sinken. Dies kann es ermöglichen, rein elektrostatisch zu fokussieren und auf komplizierte Magnetlinsen zu verzichten. Die damit erreichbare Vereinfachung des Kanonenaufbaus verringert den Kostenaufwand bei Fertigung und Wartung. Eine Fokussierung des Strahls in Breitenrichtung wird durch die gekrümmte Emissionsfläche und die radiale Beschleunigung unterstützt, die die emittierten Elektronen schon in der Elektronenkanone zum Zielbereich hin zusammenlaufen lassen.In addition, in the case of flat beams for focusing in the thickness direction, a smaller electron-optical reduction than in circular beams of the same cross-sectional area is necessary, as a result of which the demands on the electron-optical quality of a lens for focusing in this direction decrease. This may allow to focus purely electrostatically and to dispense with complicated magnetic lenses. The achievable simplification of the gun construction reduces the cost of production and maintenance. Focusing of the beam in the width direction is assisted by the curved emission surface and the radial acceleration, which cause the emitted electrons to converge towards the target region already in the electron gun.

In einer bevorzugten Ausführungsform der Erfindung ist die Beschleunigungsvorrichtung dazu ausgebildet, die Elektronen in Dickenrichtung abzulenken. Dadurch ermöglicht die Elektronenkanone eine Strahlführung, die nicht auf eine Ebene beschränkt ist.In a preferred embodiment of the invention, the accelerating device is designed to deflect the electrons in the thickness direction. This allows the electron gun a beam guide that is not limited to one plane.

Gemäß einer weiteren bevorzugten Ausführungsform der Erfindung ist die Beschleunigungsvorrichtung zusätzlich dazu ausgebildet, den Elektronen-Flachstrahl in Dickenrichtung zu fokussieren. Dies ermöglicht vorteilhafterweise die Erzeugung eines fokussierten Elektronen-Flachstrahls.According to a further preferred embodiment of the invention, the acceleration device is additionally designed to to focus the electron flat beam in the thickness direction. This advantageously allows the generation of a focused flat electron beam.

Gemäß einer weiteren bevorzugten Ausführungsform ist die Breite der Emissionsfläche mindestens einhundertmal, vorzugsweise mindestens eintausendmal größer als ihre Höhe. Bei konstantem Gesamtstrom und konstanter Höhe der Emissionsfläche führt eine größere Breite zu einer Reduktion der Stromdichte und damit der Raumladungskräfte an der Kathode. Da Raumladungskräfte insbesondere in den Bereichen, in denen der Elektronen-Flachstrahl langsam ist, einen großen Einfluss auf die Strahlqualität haben, lässt sich durch eine geringere Raumladungsdichte an der Kathode auf vorteilhafte Weise eine Verbesserung der Emittanz des Strahls erreichen.According to a further preferred embodiment, the width of the emission surface is at least one hundred times, preferably at least one thousand times greater than its height. With constant total current and constant height of the emission surface, a larger width leads to a reduction in the current density and thus the space charge forces at the cathode. Since space charge forces, in particular in the areas in which the flat electron beam is slow, have a great influence on the beam quality, an improvement in the emittance of the beam can advantageously be achieved by a lower space charge density at the cathode.

Gemäß einer weiteren bevorzugten Ausführungsform der Erfindung ist die Emissionsfläche der Kathode als geschlossener Ring ausgebildet. Hierdurch weist die Kathode in Breitenrichtung keine Randflächen auf, deren Streufelder eine Ablenkung des Elektronen-Flachstrahls bewirken könnten. Außerdem kompensieren sich die Raumladungskräfte auf ein einzelnes Elektron in Breitenrichtung, so dass eine radiale Strahlführung wesentlich erleichtert wird.According to a further preferred embodiment of the invention, the emission surface of the cathode is formed as a closed ring. As a result, the cathode has no edge surfaces in the width direction whose stray fields could cause a deflection of the electron flat beam. In addition, the space charge forces compensate for a single electron in the width direction, so that a radial beam guidance is much easier.

Gemäß einer weiteren bevorzugten Ausführungsform der Erfindung weist eine Strahlrichtung im Zielbereich nicht zu der Emissionsfläche der Kathode. Hierdurch lässt sich - insbesondere bei einer ringförmigen Ausführung der Emissionsfläche - vermeiden, dass Elektronen, die entlang der betreffenden Strahlrichtung den Zielbereich durchqueren, wieder auf der Emissionsfläche auftreffen. Andernfalls könnte die Emissionsfläche durch ein Aufheizen oder elektroneninduzierte Adsorption von Fremdatomen beschädigt werden.According to a further preferred embodiment of the invention, a beam direction in the target area does not lead to the emission area of the cathode. As a result, it is possible, in particular in the case of an annular embodiment of the emission surface, to prevent electrons traversing the target region along the relevant beam direction from hitting the emission surface again. Otherwise, the emission surface could be damaged by heating or electron-induced adsorption of foreign atoms.

Gemäß einer weiteren bevorzugten Ausführungsform der Erfindung steht eine Strahlrichtung am Ort der Kathode nicht senkrecht auf der Zentralachse. Alternativ oder zusätzlich dazu steht gemäß einer anderen bevorzugten Ausführungsform eine Strahlrichtung im Zielbereich nicht senkrecht auf der Zentralachse. Hierdurch kann ebenfalls vermieden werden, dass Elektronen, die entlang der betreffenden Strahlrichtung die Kathode verlassen und/oder den Zielbereich durchqueren, auf einem gegenüberliegenden Teil der Emissionsfläche auftreffen.According to a further preferred embodiment of the invention, a beam direction at the location of the cathode is not perpendicular to the central axis. Alternatively or in addition According to another preferred embodiment, a beam direction in the target area is not perpendicular to the central axis. In this way, it can likewise be avoided that electrons which leave the cathode along the relevant beam direction and / or pass through the target area impinge on an opposite part of the emission surface.

Gemäß einer weiteren bevorzugten Ausführungsform der Erfindung ist eine Randfläche einer Elektrode der Beschleunigungsvorrichtung als Segment einer Rotationsfläche ausgebildet, wobei die Rotationsachse der Fläche parallel zur Zentralachse orientiert ist. Dies ermöglicht eine besonders einfache und kompakte Ausführung der Beschleunigungsvorrichtung zur radialen Beschleunigung der Elektronen in Richtung des Zielbereichs an der Zentralachse.According to a further preferred embodiment of the invention, an edge surface of an electrode of the acceleration device is formed as a segment of a surface of revolution, wherein the axis of rotation of the surface is oriented parallel to the central axis. This allows a particularly simple and compact design of the accelerator device for the radial acceleration of the electrons in the direction of the target area at the central axis.

Gemäß einer weiteren bevorzugten Ausführungsform umfasst das Rotationsflächensegment, das eine Randfläche einer Elektrode bildet, einen Rotationswinkel von dreihundertsechzig Grad. Dies ermöglicht eine kompakte und einfache Bauform der Beschleunigungsvorrichtung, insbesondere, aber nicht ausschließlich, wenn alle den Elektronen zugewandten Randflächen der Beschleunigungsvorrichtung in dieser Weise ausgebildet sind. Zusätzlich werden Streufelder an den die Rotationsflächen azimutal begrenzenden Randflächen vermieden, was eine Strahlführung in radialer Richtung erleichtert.According to another preferred embodiment, the rotational surface segment forming an edge surface of an electrode comprises a rotation angle of three hundred and sixty degrees. This allows a compact and simple design of the accelerating device, in particular, but not exclusively, when all the edge surfaces facing the electrons of the accelerating device are formed in this way. In addition, stray fields at the azimuthally limiting surfaces of rotation are avoided, which facilitates beam guidance in the radial direction.

Eine ringförmige Ausbildung der Beschleunigungsvorrichtung erlaubt es außerdem, den Elektronen-Flachstrahl in Breitenrichtung alleine durch eine radiale Strahlführung auf den Zielbereich zu fokussieren. Es entfallen also ansonsten eventuell notwendige Elemente, die eine Fokussierung in Breitenrichtung bewirken, was den Aufbau des Gesamtsystems vereinfacht. Außerdem werden durch eine ringförmige Ausgestaltung auf besonders einfache Weise am Ort der Kathode eine geringe Stromdichte und eine reduzierte Raumladungswirkung realisiert, während gleichzeitig die Stromdichte der Elektronen im Zielbereich hoch sein kann.An annular formation of the accelerating device also makes it possible to focus the flat electron beam in the width direction alone by a radial beam guidance on the target area. It thus eliminates otherwise possibly necessary elements that cause a focus in the width direction, which simplifies the structure of the overall system. In addition, a small current density and a reduced space charge effect are realized by an annular configuration in a particularly simple manner at the location of the cathode, while at the same time the current density of the electrons in the target area can be high.

Gemäß einer weiteren bevorzugten Ausführungsform weist die Beschleunigungsvorrichtung eine Einrichtung zur Erzeugung eines Magnetfeldes auf. Dies ermöglicht vorteilhafterweise eine magnetische Ablenkung der Elektronen. Eine magnetfeldgestützte Strahlführung und -fokussierung erlaubt es, elektronenoptische Elemente mit kleinen Abbildungsfehlern zu realisieren, was die erreichbare Fokusgröße weiter reduzieren kann.According to a further preferred embodiment, the acceleration device has a device for generating a magnetic field. This advantageously allows a magnetic deflection of the electrons. Magnetic field-guided beam guidance and focusing makes it possible to realize electron-optical elements with small aberrations, which can further reduce the achievable focus size.

Hierbei ist das Magnetfeld gemäß einer weiteren bevorzugten Ausführungsform rotationssymmetrisch zu einer Achse, die parallel zur Zentralachse ausgerichtet ist. Dadurch lässt sich die Einrichtung zur Erzeugung eines Magnetfelds vorteilhafterweise besonders einfach konstruieren.In this case, according to a further preferred embodiment, the magnetic field is rotationally symmetrical with respect to an axis which is aligned parallel to the central axis. As a result, the device for generating a magnetic field can advantageously be constructed particularly simply.

Eine Strahlungserzeugungsanlage gemäss der Erfindung weist eine Elektronenkanone der vorgenannten Art auf, in deren Zielbereich eine Zielstruktur angeordnet ist. Hier ermöglicht die gute Fokussierbarkeit des von der Elektronenkanone erzeugten Elektronen-Flachstrahls eine hohe Stromdichte auf der Zielstruktur und damit beispielsweise eine hohe Intensität der erzeugten Strahlung. Erfindungsgemäss wird die Zielstruktur als Röntgentarget ausgebildet. Hierdurch kann eine besonders kompakte Röntgenquelle hoher Intensität realisiert werden.A radiation generating system according to the invention has an electron gun of the aforementioned type, in whose target area a target structure is arranged. Here, the good focussability of the electron flat-beam generated by the electron gun allows a high current density on the target structure and thus, for example, a high intensity of the generated radiation. According to the invention, the target structure is formed as an X-ray target. As a result, a particularly compact x-ray source of high intensity can be realized.

Gemäß einer weiteren bevorzugten Ausführung der Strahlungserzeugungsanlage ist die Beschleunigungsvorrichtung der Elektronenkanone dazu ausgebildet, die Elektronen auf eine Energie von mindestens 25keV, bevorzugt auf eine Energie von mindestens 100keV zu beschleunigen. Dies ermöglicht eine besonders effiziente Erzeugung von kurzwelligem Röntgenlicht.According to a further preferred embodiment of the radiation generating system, the accelerator device of the electron gun is designed to accelerate the electrons to an energy of at least 25 keV, preferably to an energy of at least 100 keV. This enables a particularly efficient generation of short-wave X-ray light.

Die oben beschriebenen Eigenschaften, Merkmale und Vorteile dieser Erfindung sowie die Art und Weise, wie diese erreicht werden, werden klarer und deutlicher verständlich im Zusammenhang mit der folgenden Beschreibung der Ausführungsbeispiele, die im Zusammenhang mit den Zeichnungen näher erläutert werden. Es zeigen in jeweils schematischer Darstellung:

Figur 1
eine Gesamtansicht eines Querschnitts einer Elektronenkanone;
Figur 2
eine perspektivische Darstellung eines Segments einer Elektronenkanone;
Figur 3
eine Detailansicht eines Querschnitts einer Elektronenkanone mit ringförmiger Emissionsfläche und einer Beschleunigungsvorrichtung; und
Figur 4
eine Detailansicht eines Querschnitts einer Elektronenkanone mit ringförmiger Emissionsfläche und einer Beschleunigungsvorrichtung.
The above-described characteristics, features and advantages of this invention and the manner in which it achieves will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings. Shown schematically in each case:
FIG. 1
an overall view of a cross section of an electron gun;
FIG. 2
a perspective view of a segment of an electron gun;
FIG. 3
a detailed view of a cross section of an electron gun with an annular emission surface and an accelerator device; and
FIG. 4
a detailed view of a cross section of an electron gun with an annular emission surface and an accelerator.

In Figur 1 ist die Schnittansicht einer Elektronenkanone 1 schematisch dargestellt. Die Elektronenkanone 1 erlaubt es, einen Elektronen-Flachstrahl zu erzeugen und diesen sowohl in Dicken- als auch in Breitenrichtung zu fokussieren. Während eine Fokussierung in Dickenrichtung durch elektronenoptische Elemente realisiert wird, wird eine Fokussierung in Breitenrichtung durch eine radiale Strahlführung erreicht. Hierzu sind alle Elemente dieses Ausführungsbeispiels rotationssymmetrisch um eine Zentralachse 20 angeordnet. Zusätzlich zur Rotationssymmetrie weist der gesamte Aufbau eine Spiegelsymmetrie bezüglich einer mittig angeordneten Strahlebene 11 auf.In FIG. 1 the sectional view of an electron gun 1 is shown schematically. The electron gun 1 makes it possible to generate a flat electron beam and to focus it both in the thickness and in the width direction. While focusing in the thickness direction is realized by electron-optical elements, focusing in the width direction is achieved by a radial beam guidance. For this purpose, all elements of this embodiment are arranged rotationally symmetrical about a central axis 20. In addition to the rotational symmetry, the entire structure has a mirror symmetry with respect to a centrally arranged beam plane 11.

Die dargestellte Elektronenkanone 1 umfasst eine ringförmige Kathode 100 und eine Beschleunigungsvorrichtung 200. Die Kathode 100 weist dabei eine Emissionsfläche 110 auf, welche sich auf der Innenfläche der Kathode 100 befindet und in Richtung der Zentralachse 20 ausgerichtet ist. Die Beschleunigungsvorrichtung 200 umfasst eine ebenfalls ringförmige Kathodenelektrode 230, die die Außenseite der Kathode 100 umgibt, sowie eine untere Linsenelektrode 210 und eine obere Linsenelektrode 215, die zwischen Kathode 100 und Zentralachse 20 angeordnet sind. Des Weiteren umfasst die Beschleunigungsvorrichtung 200 ein unteres Anodenelement 220 und ein oberes Anodenelement 225.The illustrated electron gun 1 comprises an annular cathode 100 and an accelerator 200. The cathode 100 has an emitting surface 110 which is located on the inner surface of the cathode 100 and oriented in the direction of the central axis 20. The accelerator 200 includes a likewise annular cathode electrode 230 surrounding the outside of the cathode 100, and a lower lens electrode 210 and an upper lens electrode 215 disposed between the cathode 100 and the central axis 20 are arranged. Furthermore, the accelerator 200 includes a lower anode member 220 and an upper anode member 225.

Die Kathode 100 ist als Rotationskörper mit einer Rotationsachse 101, die Elemente der Beschleunigungsvorrichtung 200 als Rotationskörper mit einer gemeinsamen Rotationsachse 201 ausgebildet. In der dargestellten Ausführung fallen die Rotationsachsen 101, 201 von Kathode 100 und Beschleunigungsvorrichtung 200 mit der Mittenachse 20 zusammen. Es sind allerdings auch Ausführungen möglich, bei denen zwei oder alle drei Achsen nicht aufeinander liegen, sondern lediglich parallel zueinander angeordnet sind. Ebenso können die einzelnen Elemente 210, 215, 220, 225, 230 der Beschleunigungsvorrichtung 200 unterschiedlich angeordnete Rotationsachsen aufweisen.The cathode 100 is designed as a rotation body with a rotation axis 101, and the elements of the acceleration device 200 as a rotation body with a common rotation axis 201. In the illustrated embodiment, the axes of rotation 101, 201 of the cathode 100 and accelerator 200 coincide with the center axis 20. However, embodiments are also possible in which two or all three axes do not lie on top of each other but are only arranged parallel to one another. Likewise, the individual elements 210, 215, 220, 225, 230 of the acceleration device 200 may have differently arranged axes of rotation.

Die Kathode 100 und die Kathodenelektrode 230 bilden bei der dargestellten Elektronenkanone 1 einen äußeren Ring um die Zentralachse 20. Im Inneren dieses Rings sind konzentrisch die ebenfalls ringförmigen Linsenelektroden 210, 215 angeordnet. Dabei liegen die untere Linsenelektrode 210 und die obere Linsenelektrode 215 symmetrisch zueinander auf jeweils einer Seite der Strahlebene 11. Elektronen, die von der Emissionsfläche 110 der Kathode 100 emittiert werden, bewegen sich entlang der Strahlebene 11 im Zwischenraum zwischen den Linsenelektroden 210, 215 radial nach innen auf einen Zielbereich 30 zu, der sich im Zentrum der Elektronenkanone 11 an der Zentralachse 20 befindet.In the illustrated electron gun 1, the cathode 100 and the cathode electrode 230 form an outer ring around the central axis 20. The ring-shaped lens electrodes 210, 215, which are likewise annular, are arranged concentrically in the interior of this ring. In this case, the lower lens electrode 210 and the upper lens electrode 215 are symmetrical to each other on one side of the beam plane 11. Electrons emitted from the emission surface 110 of the cathode 100 move radially along the beam plane 11 in the space between the lens electrodes 210, 215 inside to a target area 30, which is located in the center of the electron gun 11 on the central axis 20.

Dort sind auch das untere Anodenelement 220 und das obere Anodenelement 225 angeordnet, welche beide kegelförmig ausgebildet sind. Wie die Linsenelektroden 210, 215 liegen sie symmetrisch zueinander auf gegenüberliegenden Seiten der Strahlebene 11, so dass beschleunigte Elektronen den entstehenden Zwischenraum entlang der Strahlebene 11 durchqueren können.There, the lower anode element 220 and the upper anode element 225 are arranged, both of which are conical. Like the lens electrodes 210, 215, they lie symmetrically on opposite sides of the beam plane 11, so that accelerated electrons can traverse the resulting gap along the beam plane 11.

Zur besseren Illustration, insbesondere der Ausgestaltung der Kathode 100, zeigt Figur 2 eine perspektivische schematische Darstellung eines Segments der Elektronenkanone 1. Bedingt durch die rotationssymmetrische Ausführung der Linsenelektroden 210, 215 bilden die Oberflächen dieser Elektroden Rotationsflächen. Im dargestellten Ausführungsbeispiel der Elektronenkanone 1 bewegen sich die Elektronen insbesondere entlang einer Randfläche 211 der unteren Linsenelektrode 210 und einer Randfläche 216 der oberen Linsenelektrode 215.For better illustration, in particular the embodiment of the cathode 100, shows FIG. 2 a perspective schematic representation of a segment of the electron gun 1. Due to the rotationally symmetrical design of the lens electrodes 210, 215, the surfaces of these electrodes form surfaces of revolution. In the illustrated embodiment of the electron gun 1, the electrons move in particular along an edge surface 211 of the lower lens electrode 210 and an edge surface 216 of the upper lens electrode 215.

Die Emissionsfläche 110 der Kathode 100 weist eine Breite 120 auf, die mindestens zehnmal größer ist als eine Höhe 130, die senkrecht zur Breite 120 entlang der Emissionsfläche gemessen wird. Breite und Höhe sind jeweils entlang der Emissionsfläche 110 definiert, wobei eine azimutale oder Breitenrichtung 125 die Richtung bezeichnet, in der die Emissionsfläche 110 die Krümmung um die Zentralachse 20 aufweist. Im Allgemeinen muss die Krümmung der Emissionsfläche 110 entlang der Breitenrichtung 125 nicht konstant sein. Neben einer durch die Ringform bedingten Krümmung entlang der Breitenrichtung 125 weist die Emissionsfläche 110 im dargestellten Ausführungsbeispiel auch eine Krümmung entlang ihrer Höhe 120 auf.The emission surface 110 of the cathode 100 has a width 120 which is at least ten times greater than a height 130 which is measured perpendicular to the width 120 along the emission surface. Width and height are each defined along the emission surface 110, with an azimuthal or width direction 125 designating the direction in which the emission surface 110 has the curvature about the central axis 20. In general, the curvature of the emission surface 110 along the width direction 125 need not be constant. In addition to a curvature caused by the ring shape along the width direction 125, the emission surface 110 in the illustrated embodiment also has a curvature along its height 120.

Die Emissionsfläche 110 umfasst dabei definitionsgemäß den Bereich der Oberfläche der Kathode 100, von dem aufgrund der Ausgestaltung der Elektronenkanone 1 Elektronen bis zum Zielbereich 30 geführt werden. Insbesondere kann die Emissionsfläche 110 auch durch eine Blende, die zwischen Kathode 100 und Zielbereich 30 angeordnet ist und den emittiert Strahl begrenzt, definiert werden.By definition, the emission surface 110 comprises the region of the surface of the cathode 100, from which electrons are guided to the target region 30 due to the configuration of the electron gun 1. In particular, the emission surface 110 can also be defined by a diaphragm which is arranged between the cathode 100 and the target region 30 and which delimits the emitted beam.

Figur 3 zeigt eine weitere Darstellung der Elektronenkanone 1, in der zudem beispielhaft ein erzeugter Elektronen-Flachstrahl 10 im Querschnitt dargestellt ist. FIG. 3 shows a further illustration of the electron gun 1, in addition also exemplified a generated flat electron beam 10 is shown in cross section.

Die Kathode 100 und die untere bzw. obere Linsenelektrode 210, 215 sind so angeordnet, dass emittierte Elektronen an jedem Ort der Emissionsfläche 110 in einer jeweils radialen Richtung 140 zum Zielbereich hin beschleunigt werden können. Hierzu sind die Kathode 100 und die Linsenelektroden 210, 215 zusätzlich so ausgebildet, dass an die Kathode 100 eine negative Spannung mit Bezug auf die Linsenelektroden 210, 215 angelegt werden kann. Durch die radiale Beschleunigung bildet sich im Betrieb der Elektronenkanone 1 ein scheibenförmiger Elektronen-Flachstrahl 10 aus, der symmetrisch um die Strahlebene 11 angeordnet ist.The cathode 100 and the lower and upper lens electrodes 210, 215 are arranged so that emitted electrons Each location of the emission surface 110 can be accelerated in a respective radial direction 140 toward the target area. For this, the cathode 100 and the lens electrodes 210, 215 are additionally formed so that a negative voltage with respect to the cathode electrodes 210, 215 can be applied to the cathode 100. As a result of the radial acceleration, during operation of the electron gun 1, a disk-shaped flat electron beam 10 is formed, which is arranged symmetrically about the beam plane 11.

Elektronen, die in einem Fokussierbereich 250 wieder aus dem Bereich zwischen den Linsenelektroden 210, 215 austreten, werden anschließend weiter auf die gewünschte Endgeschwindigkeit im Zielbereich 30 beschleunigt. Hierzu kann zwischen den Anodenelementen 220, 225 und den Linsenelektroden 210, 215 ebenfalls eine elektrische Spannung angelegt werden. Die inneren Randflächen der Linsenelektroden 210, 215 und die Randflächen der Anodenelemente 220, 225 sind zusätzlich so geformt, dass sich bei Spannungsbelegung in einem Fokussierbereich 250 ein elektrisches Feld ausbildet, in dem der Elektronen-Flachstrahl 10 in einer Dickenrichtung 150, welche in der gezeigten Ausführung an jedem Ort parallel zur Zentralachse 20 orientiert ist, fokussiert wird.Electrons which exit the region between the lens electrodes 210, 215 in a focusing region 250 are then further accelerated to the desired final velocity in the target region 30. For this purpose, an electrical voltage can also be applied between the anode elements 220, 225 and the lens electrodes 210, 215. The inner edge surfaces of the lens electrodes 210, 215 and the edge surfaces of the anode elements 220, 225 are additionally formed such that when voltage is applied in a focusing region 250 an electric field is formed, in which the flat electron beam 10 in a thickness direction 150, which in the shown Embodiment is oriented at each location parallel to the central axis 20, is focused.

Eine beispielhafte Spannungsbelegung, um den skizzierten Strahlverlauf bei einer Strahlenergie von 25 keV bis 200 keV zu erhalten, ist, bezogen auf das Kathodenpotential, eine Spannung von 25 kV bis 200 kV auf den Anodenelementen 220, 225. Die Linsenelektroden 210, 215 sind dann mit etwa einem Fünftel der Anodenspannung beaufschlagt, also etwa 5 kV bis 40 kV. Bevorzugt werden die Anodenelemente 220, 225 mit 50 kV und die Linsenelektroden 210, 215 mit 10 kV beaufschlagt, besonders bevorzugt mit 100 kV bzw. 20 kV. Eine Strahlenergie von 25 keV bis 200 keV stellt beispielsweise einen sinnvollen Energiebereich zur Röntgenlichterzeugung dar, bei dem in konventionellen Röntgentargets ein für zum Beispiel medizinische Anwendungen geeignetes Röntgenspektrum erzeugt wird.An exemplary voltage assignment to obtain the sketched beam path at a beam energy of 25 keV to 200 keV is, based on the cathode potential, a voltage of 25 kV to 200 kV on the anode elements 220, 225. The lens electrodes 210, 215 are then with about one fifth of the anode voltage is applied, that is about 5 kV to 40 kV. Preferably, the anode elements 220, 225 are applied with 50 kV and the lens electrodes 210, 215 with 10 kV, particularly preferably with 100 kV or 20 kV. For example, a beam energy of 25 keV to 200 keV represents a sensible energy range for the generation of X-ray light, in which an X-ray spectrum suitable for medical applications, for example, is generated in conventional X-ray targets.

Zur Fokussierung des Elektronen-Flachstrahls 10 auf den Zielbereich 30 gelangen in Breitenrichtung 125 und Dickenrichtung 150 zwei unterschiedliche Methoden zur Anwendung. In Dickenrichtung 150 wird der Elektronen-Flachstrahl durch eine elektrostatische Linse fokussiert. Zur Fokussierung in Breitenrichtung 125 wird dagegen durch die Geometrie der Elektronenkanone 1 eine auf den Zielbereich 30 radial nach innen ausgerichtete Strahlführung verwendet, wodurch keine Ablenkung der Elektronen in Breitenrichtung 125 erforderlich ist.In order to focus the flat electron beam 10 on the target area 30, two different methods are used in the width direction 125 and the thickness direction 150. In the thickness direction 150, the flat electron beam is focused by an electrostatic lens. For focusing in the width direction 125, on the other hand, by the geometry of the electron gun 1, a beam guidance directed radially inward on the target area 30 is used, whereby no deflection of the electrons in the width direction 125 is required.

Die in den Figuren 1 bis 3 gezeigte rotationssymmetrische Ausführung der Elektronenkanone 1 hat den Vorteil, dass sich die durch die gegenseitige Abstoßung der Elektronen des Elektronen-Flachstrahls 10 erzeugten Raumladungskräfte in Breitenrichtung 125 kompensieren. Dadurch kann der Elektronen-Flachstrahl 10 nicht nur in Dickenrichtung 150, sondern auch in Breitenrichtung 125 sehr fein fokussiert werden. Die verbleibende Radialkomponente der Raumladung hat auf die erreichbare Fokusgröße eine zu vernachlässigende Auswirkung.The in the FIGS. 1 to 3 shown rotationally symmetrical design of the electron gun 1 has the advantage that compensate for the space charge forces generated in the width direction 125 by the mutual repulsion of the electrons of the flat electron beam 10. As a result, the flat electron beam 10 can be focused very finely not only in the thickness direction 150 but also in the width direction 125. The remaining radial component of the space charge has a negligible effect on the achievable focus size.

Durch die rotationssymmetrische Ausführung sind außerdem die durch die Kathode 100 und die Beschleunigungsvorrichtung 200 erzeugten Felder in Breitenrichtung 125 homogen und hängen nur von der radialen Entfernung der Elektronen von der Zentralachse 20 ab. Daher treten in Breitenrichtung 125 keine Randfelder auf, die zu einer Ablenkung des Strahls führen könnten.Due to the rotationally symmetrical design, the fields generated by the cathode 100 and the accelerating device 200 in the width direction 125 are also homogeneous and depend only on the radial distance of the electrons from the central axis 20. Therefore, no edge fields occur in the width direction 125, which could lead to a deflection of the beam.

Die in Figur 1 bis 3 dargestellte Elektronenkanone 1 ermöglicht eine große Emissionsfläche 110 im Randbereich der Elektronenkanone 1 und damit eine geringe Elektronendichte an den Stellen, in denen die Elektronen noch langsam sind. Dies wirkt sich vorteilhaft auf die Strahlqualität aus, da Raumladungen diese besonders in den Bereichen beeinflussen, in denen die entstehenden Kräfte die Elektronen auf Geschwindigkeiten beschleunigen können, die vergleichbar mit der longitudinalen Geschwindigkeit des Strahls sind.In the Figure 1 to 3 shown electron gun 1 allows a large emission area 110 in the edge region of the electron gun 1 and thus a low electron density at the points where the electrons are still slow. This has a beneficial effect on the beam quality, since space charges affect them especially in those areas where the resulting forces can accelerate the electrons to velocities comparable to the longitudinal velocity of the beam.

Eine für Raumladungseffekte kritische Dichte erreicht der Elektronen-Flachstrahls 10 erst in der Nähe des Zielbereichs 30 statt, wo solch eine hohe Dichte erwünscht ist und die Elektronen so schnell sind, dass Raumladungskräfte nur noch eine untergeordnete Rolle spielen. Trotz der Verwendung eines Elektronen-Flachstrahls lässt sich durch die dargestellte Strahlführung in radialer Richtung 140 eine isotrope Strahlform im Zielbereich 30 erreichen.A critical density for space charge effects is achieved by the flat electron beam 10 only in the vicinity of the target area 30, where such a high density is desired and the electrons are so fast that space charge forces only play a minor role. Despite the use of an electron flat jet, an isotropic beam shape in the target region 30 can be achieved by the illustrated beam guidance in the radial direction 140.

Die flache Strahlform erlaubt es außerdem, kleine Brennpunkte im Zielbereich 30 mit einer moderaten elektronenoptischen Verkleinerung zu erreichen. Dadurch sinken die Anforderungen an die Abbildungsqualität der Elektronenlinse, die durch das elektrische Feld im Fokussierbereich 250 gebildet wird. Insbesondere ist es möglich, rein elektrostatische Linsen mit verhältnismäßig großen sphärischen Aberrationen zu verwenden und es kann auf aufwendige Linsenformen, wie beispielsweise magnetische Immersionslinsen verzichtet werden.The flat beam shape also makes it possible to achieve small foci in the target area 30 with a moderate electron optical reduction. As a result, the requirements for the imaging quality of the electron lens, which is formed by the electric field in the focusing region 250, decrease. In particular, it is possible to use purely electrostatic lenses with relatively large spherical aberrations and it can be dispensed with elaborate lens shapes, such as magnetic immersion lenses.

Die Vorteile, die durch ein großes Breiten-zu-Höhen-Verhältnis der Emissionsfläche 110 erzielt werden, fallen besonders deutlich aus, wenn die Breite 120 mindestens einhundertmal, besser noch mindestens eintausendmal größer ist als die Höhe 130. Zum Vergleich erfordert beispielsweise eine Emissionsfläche von 30 mm2 eine runde Kathode mit einem Durchmesser von ungefähr 6 mm. Eine Perveanz von 2*10^-6 A/V^ (3/2) ergibt einen minimalen primären Fokus von ca. 0,6 mm. Um nun einen Brennfleck von 50 µm zu realisieren, ist eine elektronenoptische Verkleinerung von eins zu zwölf erforderlich. Dagegen kann eine Emissionsfläche derselben Größe durch einen 300 mm breiten und 100 µm hohen ringförmigen Streifen realisiert werden. Das benötigte Verkleinerungsverhältnis in Dickenrichtung 150 beträgt dann nur noch eins zu zwei und kann mit elektrostatischen Linsen erreicht werden.The advantages achieved by a large width-to-height ratio of the emitting surface 110 are particularly pronounced when the width 120 is at least one hundred times, better yet at least one thousand times greater than the height 130. For comparison, for example, requires an emission area of 30 mm 2 a round cathode with a diameter of about 6 mm. A perveance of 2 * 10 ^ -6 A / V ^ (3/2) gives a minimum primary focus of about 0.6 mm. To realize now a focal spot of 50 microns, an electron optical reduction of one to twelve is required. In contrast, an emission surface of the same size can be realized by a 300 mm wide and 100 μm high annular strip. The required reduction ratio in the thickness direction 150 is then only one to two and can be achieved with electrostatic lenses.

Die dargestellte geschlossene Anordnung des Emissionsbereichs 110 um den Zielbereich 30 und die Ausgestaltung der Anodenelemente 220, 225 als Kegel im Zentrum sind nur eine mögliche Ausführungsvariante. Insbesondere ist es denkbar, die Anodenelemente 220, 225 ebenfalls ringförmig um den Zielbereich 30 zu legen. Es ist beispielsweise auch möglich, auf die Linsenelektroden 210, 215 zu verzichten, so dass die Beschleunigungsvorrichtung 200 nur aus der Kathodenelektrode 230 und den Anodenelementen 220, 225 bestehen. Eine Fokussierung des Elektronen-Flachstrahls 10 kann dann durch eine geeignete Ausformung der Elektrodenoberflächen erreicht werden.The illustrated closed arrangement of the emission area 110 around the target area 30 and the configuration of the anode elements 220, 225 as cones in the center are just one possible variant. In particular, it is conceivable to likewise place the anode elements 220, 225 in a ring around the target area 30. For example, it is also possible to dispense with the lens electrodes 210, 215 so that the accelerator 200 only consists of the cathode electrode 230 and the anode elements 220, 225. A focusing of the electron flat beam 10 can then be achieved by a suitable shaping of the electrode surfaces.

Ebenso kann die Beschleunigungsvorrichtung 200 aus mehr Elektroden als der Kathodenelektrode 230, den Linsenelektroden 210, 215 und den Anodenelementen 220, 225 bestehen. So ist zum Beispiel eine separate Ausführung von Elektroden, die die Elektronen von der Kathode abziehen, und Elektroden, die den Elektronen-Flachstrahl 10 fokussieren, möglich. Ebenso könnte, anstatt der gezeigten separaten Ausführung der Kathodenelektrode 230, diese auch mit der Kathode 100 zu einem einzigen Element zusammengefasst werden.Likewise, the accelerator 200 may consist of more electrodes than the cathode electrode 230, the lens electrodes 210, 215 and the anode elements 220, 225. For example, a separate design of electrodes that pull the electrons from the cathode and electrodes that focus the flat electron beam 10 is possible. Likewise, rather than the separate embodiment of the cathode electrode 230 shown, these could also be combined with the cathode 100 into a single element.

Je nach Ausgestaltung der Kathode 100 und eventuell nachfolgend angeordneter Blendenelemente kann es auch mehr als nur die eine Emissionsfläche 110 geben. Außerdem ist es möglich, die Höhe 130 entlang der Breitenrichtung 125 und die Breite 120 entlang einer Höhenrichtung 120 zu variieren, anstatt diese, wie in den Figuren dargestellt, konstant zu halten.Depending on the design of the cathode 100 and possibly subsequently arranged diaphragm elements, there may be more than just one emission surface 110. In addition, it is possible to vary the height 130 along the width direction 125 and the width 120 along a height direction 120, instead of keeping them constant as shown in the figures.

Des Weiteren müssen die dem Elektronen-Flachstrahl 10 zugewandten Elektrodenoberflächen, beispielsweise eine Fläche 211 der unteren Linsenelektrode 210 und/oder eine Fläche 216 der oberen Linsenelektrode 215, nicht zwingend als Rotationsflächen ausgeführt werden, um die gewünschte Strahlführung in radialer Richtung 140 zu erreichen. So ist es beispielsweise denkbar, weitere Elemente wie radiale Nuten oder Stege an den Elektroden anzubringen, um eine zusätzliche Strahlformung zu ermöglichen. Hierzu können natürlich neben den in Figur 1 bis 3 dargestellten Elementen auch noch zusätzliche Elektroden und Blenden in die Elektronenkanone 1 integriert werden. Entscheidend bei all diesen Modifikationen ist lediglich, dass das elektrische Feld, das sich bei Spannungsbeaufschlagung der Elektroden ergibt, weiterhin eine Strahlführung in primär radialer Richtung 140 ermöglicht.Furthermore, the electrode surfaces facing the electron flat beam 10, for example a surface 211 of the lower lens electrode 210 and / or a surface 216 of the upper lens electrode 215, need not necessarily be designed as rotation surfaces in order to achieve the desired beam guidance in the radial direction 140. Thus, it is conceivable, for example, to attach further elements such as radial grooves or webs to the electrodes in order to allow additional beam shaping. This can of course be in addition to the in Figure 1 to 3 also shown additional elements and diaphragms are integrated into the electron gun 1. critical with all these modifications, it is merely that the electric field which results when voltage is applied to the electrodes, further enables beam guidance in the primarily radial direction 140.

In den gezeigten Ausführungsbeispielen sind sowohl die Kathode 10, die Kathodenelektrode 230, als auch die Linsenelektroden 210, 215 und die Anodenelemente 220, 225 als Rotationskörper ausgebildet. Es ist allerdings auch eine segmentweise Ausgestaltung möglich, bei der insbesondere die Emissionsfläche der Kathode 110 und/oder eine oder mehrere Randflächen der unteren Linsenelektrode 210 und/oder eine oder mehrere Randflächen der oberen Linsenelektrode 216 lediglich als Segmente einer Rotationsfläche ausgebildet sind. Die Segmente umfassen dabei anstatt der in den Figuren 1 und 3 gezeigten dreihundertsechzig Grad beispielsweise lediglich neunzig oder einhundertachtzig Grad. Vorzugsweise ist eine Rotationsachse 219 der entsprechenden Randflächen parallel zur Mittenachse 20 orientiert und fällt besonders bevorzugt mit dieser zusammen.In the embodiments shown, both the cathode 10, the cathode electrode 230, and the lens electrodes 210, 215 and the anode elements 220, 225 are formed as a rotational body. However, it is also possible a segmental configuration in which in particular the emission surface of the cathode 110 and / or one or more edge surfaces of the lower lens electrode 210 and / or one or more edge surfaces of the upper lens electrode 216 are formed only as segments of a rotation surface. The segments include instead of in the FIGS. 1 and 3 three hundred and sixty degrees, for example, only ninety or one hundred and eighty degrees. Preferably, a rotation axis 219 of the corresponding edge surfaces is oriented parallel to the center axis 20 and particularly preferably coincides therewith.

Diese Ausführung entspräche der schematischen Darstellung in Figur 2, wobei die Elektroden ausschließlich aus den dargestellten Segmenten bestünden. Abhängig von einem Öffnungswinkel 213 der Rotationsflächensegmente der Linsenelektroden 210, 215 und von einem Öffnungswinkel 111 des Rotationsflächensegments der Emissionsfläche 110 könnten bei einer solchen Ausführung zusätzliche Randelektroden vorgesehen werden, um den Einfluss von Streufeldern an den Segmenträndern zu minimieren.This embodiment would correspond to the schematic representation in FIG. 2 , wherein the electrodes consist exclusively of the illustrated segments. Depending on an aperture angle 213 of the rotational surface segments of the lens electrodes 210, 215 and an aperture angle 111 of the rotational surface segment of the emitting surface 110, in such an embodiment additional edge electrodes could be provided to minimize the influence of stray fields at the segment edges.

Grundsätzlich ist auch eine Ausführung der Kathode 100, der Kathodenelektrode 230, der Linsenelektroden 210, 215 und der Anodenelemente 220, 225 als Segmente eines Rotationskörpers nicht erforderlich, um gemäß der Erfindung einen Elektronen-Flachstrahl zu erzeugen, bei dem durch eine radial konvergente Strahlführung eine Fokussierung in Breitenrichtung 125 unterstützt wird. Eine gekrümmte Ausführung der Emissionsfläche 110 mit einer nicht notwendigerweise konstanten Krümmung und ein entsprechend großes Verhältnis aus Breite 120 und Höhe 130 der Emissionsfläche 110 sind ausreichend.Basically, an embodiment of the cathode 100, the cathode electrode 230, the lens electrodes 210, 215 and the anode elements 220, 225 as segments of a rotating body is not required to produce according to the invention, a flat electron beam, in which by a radially convergent beam guide Focusing in the width direction 125 is supported. A curved version of the emission surface 110 with a not necessarily constant curvature and a correspondingly large ratio of width 120 and height 130 of the emission surface 110 are sufficient.

Gemäß einer weiteren Ausführungsform der Elektronenkanone 1 kann die Beschleunigungsvorrichtung 200 neben den Linsenelektroden 210, 215 auch eine Einrichtung zur Erzeugung eines Magnetfelds 240, 245 umfassen, die beispielsweise aus einem unteren Magnetfelderzeugungselement 240 und einem oberen Magnetfelderzeugungselement 245 besteht, welche in Figur 1 dargestellt sind. Dies erlaubt eine zusätzliche, geschwindigkeitsabhängige Ablenkung der Elektronen. Dabei kann es vorteilhaft sein, dass die Einrichtung zur Erzeugung eines Magnetfeldes 240, 245 ein rotationssymmetrisches Magnetfeld erzeugt, mit einer Rotationsachse 242, die mit der Zentralachse 20 zusammenfällt. Hierdurch wird die Symmetrie des Aufbaus nicht gestört.According to another embodiment of the electron gun 1, the accelerator 200 may include, in addition to the lens electrodes 210, 215, means for generating a magnetic field 240, 245 consisting of, for example, a lower magnetic field generating element 240 and an upper magnetic field generating element 245 shown in FIG FIG. 1 are shown. This allows an additional, speed-dependent deflection of the electrons. It may be advantageous that the device for generating a magnetic field 240, 245 generates a rotationally symmetrical magnetic field, with a rotation axis 242, which coincides with the central axis 20. As a result, the symmetry of the structure is not disturbed.

Grundsätzlich kann die beschriebene radiale Strahlführung auch eine Ablenkung des Elektronen-Flachstrahls 10 in Dickenrichtung 150 beinhalten, so dass dieser nicht mehr überall in derselben Ebene verläuft. Eine solche Strahlführung kann zum Beispiel durch eine geeignete Ausgestaltung der Linsenelektroden 210, 215 der Beschleunigungsvorrichtung 200 erzielt werden. Insbesondere ist dabei auch eine gleichzeitige Ablenkung und Fokussierung des Strahls möglich.In principle, the described radial beam guidance can also include a deflection of the electron flat jet 10 in the thickness direction 150 so that it no longer runs everywhere in the same plane. Such a beam guidance can be achieved, for example, by a suitable configuration of the lens electrodes 210, 215 of the acceleration device 200. In particular, a simultaneous deflection and focusing of the beam is possible.

In Figur 4 ist mit einer Elektronenkanone 3 eine modifizierte Ausführung der Elektronenkanone 1 dargestellt, bei der die untere Linsenelektrode 210 und die obere Linsenelektrode 215 durch eine untere Ablenkelektrode 260 bzw. eine obere Ablenkelektrode 265 ersetzt wurden. Diese sind nicht mehr spiegelsymmetrisch bezüglich einer Strahlebene 12 im Kathodenbereich geformt, so dass ein Elektronen-Flachstrahl 15 im Austrittsbereich 251 am Ende der Ablenkelektroden 260, 265 parallel zur Zentralachse 20 abgelenkt wird.In FIG. 4 For example, with an electron gun 3, a modified embodiment of the electron gun 1 in which the lower lens electrode 210 and the upper lens electrode 215 have been replaced by a lower deflection electrode 260 and an upper deflection electrode 265, respectively. These are no longer mirror-symmetrically shaped with respect to a beam plane 12 in the cathode region, so that an electron flat beam 15 in the exit region 251 at the end of the deflection electrodes 260, 265 is deflected parallel to the central axis 20.

Die dargestellte Strahlführung ist unter Anderem dadurch charakterisiert, dass eine Strahlrichtung 14 im Zielbereich 30 nicht zur Emissionsfläche 110 der Kathode 100 weist. Dadurch wird vermieden, dass emittierte Elektronen auf der ihrem Emissionsort gegenüberliegenden Seite wieder auf einen Teil der Emissionsfläche 110 auftreffen können und dort die Emissionsfläche 110, zum Beispiel durch elektronenstrahlinduzierte Adsorption, kontaminieren.The illustrated beam guidance is characterized, inter alia, by the fact that a beam direction 14 in the target area 30 does not point to the emission area 110 of the cathode 100. This avoids that emitted electrons can again impinge on a part of the emission surface 110 on the side opposite to their emission site and there contaminate the emission surface 110, for example by electron beam-induced adsorption.

Dasselbe Ziel lässt sich auch erreichen, wenn die Strahlrichtung 14 im Zielbereich 30 nicht senkrecht auf der Zentralachse 20 steht, die Strahlführung ansonsten aber keine Ablenkung in Dickenrichtung 150 beinhaltet. In diesem Falle wird ein Elektronen-Flachstrahl erzeugt, der näherungsweise einen Kegelmantel bildet.The same goal can also be achieved if the beam direction 14 in the target region 30 is not perpendicular to the central axis 20, but the beam guide otherwise contains no deflection in the thickness direction 150. In this case, a flat electron beam is generated, which forms approximately a cone sheath.

Ein erneutes Auftreffen der Elektronen auf dem Emissionsbereich 110 kann auch dadurch verhindert werden, dass eine Strahlrichtung 13 im Bereich der Kathode 100 nicht senkrecht auf der Zentralachse 20 steht. Nach der Emission können die Elektronen dann zum Beispiel durch eine geeignete Ausformung und Spannungsbeaufschlagung der Kathodenelektrode 230 und/oder der Linsenelektroden 210, 215 und/oder zusätzlicher Elektroden in eine Strahlebene, die senkrecht auf der Zentralachse 20 steht, abgelenkt und anschießend weiter radial nach innen beschleunigt werden.A renewed impact of the electrons on the emission region 110 can also be prevented by a beam direction 13 in the region of the cathode 100 not being perpendicular to the central axis 20. After emission, the electrons may then be deflected, for example, by suitable shaping and applying voltage to the cathode electrode 230 and / or the lens electrodes 210, 215 and / or additional electrodes to a beam plane perpendicular to the central axis 20, and then further radially inward be accelerated.

Die Elektronenkanonen 1 bzw. 3 sind erfindungsgemäss als Bestandteil einer Strahlungserzeugungsanlage 2 ausgeführt sein, die zusätzlich eine im Zielbereich 30 angeordnete Zielstruktur 31 umfasst. Erfindungsgemäss handelt es sich hierbei um ein Target zur Erzeugung von Röntgenstrahlung. Mögliche Materialien für ein solches Röntgentarget sind zum Beispiel Wolfram, Rhenium-Wolfram Legierungen, Molybdän, Kupfer oder Kobalt. Die Zielstruktur 31 kann zum Beispiel eine zylindrische Form besitzen und symmetrisch um die Zentralachse 20 angeordnet sein.According to the invention, the electron guns 1 and 3 are designed as part of a radiation generating installation 2 which additionally comprises a target structure 31 arranged in the target area 30. According to the invention, this is a target for generating X-ray radiation. Possible materials for such an X-ray target are, for example, tungsten, rhenium-tungsten alloys, molybdenum, copper or cobalt. The target structure 31 may, for example, have a cylindrical shape and be arranged symmetrically about the central axis 20.

Obwohl die Erfindung im Detail durch die bevorzugten Ausführungsbeispiele näher illustriert und beschrieben wurde, so ist die Erfindung nicht durch die offenbarten Beispiele eingeschränkt und andere Variationen können vom Fachmann hieraus abgeleitet werden, ohne den Schutzumfang der Erfindung zu verlassen.While the invention has been further illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims (11)

  1. Radiation generating apparatus (2) for generating x-ray radiation having an electron gun (1, 3) for generating a flat electron beam (10, 15) and having a target structure (31), wherein the electron gun (1, 3) has a cathode (100) having an emission surface (110) which is curved about a central axis (20) and which is designed to emit electrons,
    and has an accelerating device (200) for accelerating the electrons in a direction (140) radial to the emission surface toward a target region (30) on the central axis (20),
    wherein the emission surface (110) has a width (120) in the azimuthal direction
    and the emission surface (110) has a height (130) oriented perpendicularly to the width (120),
    wherein the width (120) is at least ten times the magnitude of the height (130),
    wherein the target structure (31) is arranged in the target region (30) and designed as an x-ray target.
  2. Radiation generating apparatus (2) according to Claim 1, wherein the accelerating device (200) is designed to deflect the electrons in a thickness direction (150) oriented perpendicularly to a beam direction and perpendicularly to a width direction (125).
  3. Radiation generating apparatus (2) according to Claim 2, wherein the accelerating device (200) is designed to focus the flat electron beam (10, 15) in the thickness direction (150).
  4. Radiation generating apparatus (2) according to any of the preceding claims, wherein the width (120) of the emission surface (110) is at least one hundred times, preferably at least one thousand times, greater than the height (130) of the emission surface (110).
  5. Radiation generating apparatus (2) according to any of the preceding claims, wherein the emission surface (110) of the cathode (100) is designed as a closed ring.
  6. Radiation generating apparatus (2) according to any of the preceding claims, wherein the electron gun (3) has an upper deflection electrode (265) and a lower deflection electrode (260),
    wherein a mirror symmetry relative to a beam plane (12) in the region of the cathode (100) between the upper deflection electrode (265) and the lower deflection electrode (260) is broken in such a way that the flat electron beam (15) in an exit region (251) at the end of the upper and lower deflection electrodes (265, 260) is deflected parallel to the central axis (20) and a beam direction (14) in the target region (30) does not point toward the emission surface (110) of the cathode (100) .
  7. Radiation generating apparatus (2) according to any of the preceding claims, wherein an edge surface (211) of an electrode (210) of the accelerating device (200) is designed as a segment of a surface of revolution whose axis (219) of the rotation is oriented parallel to the central axis (20).
  8. Radiation generating apparatus (2) according to Claim 7, wherein the surface of revolution segment of the edge surface (211) has a rotation angle (213) of three hundred and sixty degrees.
  9. Radiation generating apparatus (2) according to any of the preceding claims, wherein the accelerating device (200) has a unit (240, 245) for generating a magnetic field.
  10. Radiation generating apparatus (2) according to Claim 9, wherein the unit (240, 245) for generating the magnetic field is designed to generate a magnetic field designed to be rotationally symmetrical about an axis parallel to the central axis (20).
  11. Radiation generating apparatus (2) according to any of the preceding claims,
    wherein the accelerating device (200) has anode elements (200, 225) which are arranged on the central axis (20) and which are embodied to have a voltage of at least 25 keV, preferably at least 100 keV, in relation to a potential of the cathode (100) applied thereto for the purposes of accelerating the electrons.
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