EP3518266A1 - Thermionic emission device - Google Patents
Thermionic emission device Download PDFInfo
- Publication number
- EP3518266A1 EP3518266A1 EP18154147.5A EP18154147A EP3518266A1 EP 3518266 A1 EP3518266 A1 EP 3518266A1 EP 18154147 A EP18154147 A EP 18154147A EP 3518266 A1 EP3518266 A1 EP 3518266A1
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- EP
- European Patent Office
- Prior art keywords
- emission surface
- main
- emitter
- heating
- emission device
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
- H01J35/06—Cathodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/13—Solid thermionic cathodes
- H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/13—Solid thermionic cathodes
- H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
- H01J1/22—Heaters
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2235/00—X-ray tubes
- H01J2235/06—Cathode assembly
- H01J2235/068—Multi-cathode assembly
Definitions
- the invention relates to a thermionic emission device.
- Such a thermionic emission device is for example from the DE 10 2009 005 454 B4 known and effective in an X-ray tube as a cathode.
- the known thermionic emission device comprises an indirectly heated main emitter, which is designed as a flat emitter with an unstructured main emission surface, and with a heating emitter, which is designed as a flat emitter with a structured heating emission surface.
- An unstructured emission surface is understood to mean a flat, substantially homogeneous emission surface without slits or similar interruptions.
- An emission surface, which is interrupted for example by slots or has a meander-shaped conductor track, is referred to as structured.
- the main emitter and the heater emitter each have at least two terminal lugs, said heater is nested in a manner possible in the main emitter.
- the main emission surface and the heating emission surface are aligned substantially parallel and centric to one another.
- the terminal lugs of the main emitter are oriented substantially perpendicular to the main emission surface and do not project beyond the main emission surface in the lateral direction.
- the quality of the focal spot is achieved with structurally simple means and avoided even at high thermal loads undesirable widening or defocusing of the electron beam.
- the electron beam generated in the thermionic emission device impinges on a rotary anode in a focal spot. Due to the focal spot profile of the electron beam, a surface temperature of up to 2,400 ° C is generated on the focal track. This surface temperature of the focal track can not be increased without undesirable shortening of the life of the rotary anode, so that only a very small increase in power over a very short period of time and a subsequent cooling phase can be realized.
- the WO 2013/080074 A1 describes the use of carbon nanotubes (carbon nanotubes) as emitters in X-ray tubes.
- An asymmetric emission of electrons is eg from the US 7,835,501 B2 known.
- an electron beam emerging from the cathode is modulated by a focal spot modulation unit such that an asymmetrical intensity distribution of the electron beam is adjustable.
- Object of the present invention is to provide a thermionic emission device for an X-ray tube, which ensures a longer life of the X-ray tube with the same image quality.
- the thermionic emission device of claim 1 comprises a flat emitter having a main emission surface switchable to a main potential and a switchable field effect electron emitter having a heating emission surface switchable to a heating potential different from the main potential.
- the main emission surface of the flat emitter is heated by electrons emitted from the heating emission surface of the field effect electron emitter.
- the field effect electron emitter thus forms an indirect heater for the flat emitter.
- the heating potential causing the emission of the electrons from the heating emission surface is different from the main potential resulting in the thermal emission of the electrons from the main emission surface of the flat emitter.
- the field-effect electron emitters can be designed, for example, as CNT-based field emitters (CNT, carbon nanotubes, carbon nanotubes) or as Si-based field emitters (Si, silicon).
- CNT CNT-based field emitters
- Si Si-based field emitters
- nanocrystalline diamond is according to the DE 197 27 606 A1 suitable for the production of cold cathodes.
- the main emission surface and the heating emission surface are structured (claim 2).
- This structuring can be realized in the case of a flat emitter with a rectangular surface, for example by means of slots on the main emission surface.
- this structuring is e.g. can be realized by a corresponding segmentation of the field effect emitter material. By such structuring, a defined focal spot is easily obtained.
- the heating emission surface to the main emission surface has a predeterminable distance (claim 3).
- the predeterminable distance between the heating emission surface and the main emission surface is, for example, between approximately 0.5 mm and 5 mm.
- CNT-based field emitters Si-based field emitters (Si, silicon) can also be used.
- Si Si-based field emitters
- the main emission surface of the thermionic emission device can advantageously be heated by the heating emission surface in a predeterminable range (claim 4).
- the heating emission surface of the thermionic emission device for this purpose comprises a predeterminable number of individually controllable field effect emitter segments (claim 5).
- the thermionic emission device according to the invention or its advantageous embodiments are suitable for installation in a focus head (claim 6).
- the radiation exposure is reduced accordingly and the recording times are shortened in the imaging.
- the illustrated thermionic emission device comprises a flat emitter 1 with a main emission surface 11 and field effect electron emitter 2 with a heating emission surface 21.
- the flat emitter 1 can be switched to a main potential U 1 and the field effect electron emitter 2 can be switched to a heating potential U 2 , which is different from the main potential U 1 .
- the heating emission surface 21 of the field effect electron emitter 2 comprises a predeterminable number of segments 22, which are applied to a substrate 23 by a metallization, for example.
- the structuring of the heating emission surface 21 is achieved in the embodiment shown by the individually controllable field effect emitter segments 22.
- the main emission surface 11 and the Bankemissions Structure 21 are structured.
- the heating emission surface 21 has a predeterminable distance 3 from the main emission surface 11.
- at least one spacer 4 is arranged in the edge region of the substrate 23, by means of which the distance 3 between the heating emission surface 21 and the main emission surface 11 is ensured.
- a U-shaped spacer 4 is provided, which is arranged on three sides and has a contact 41 for the flat emitter 1.
- a longitudinal side of the substrate 23 is not covered by the spacer 4 in order to be able to electrically contact the field-effect emitter segments 22 arranged on the substrate 23.
- the main emission surface 11 can be heated in a predefined area in a defined manner.
- FIG. 1 illustrated embodiment is not only the heating emission surface 21 of the field effect electron emitter 2, but also the main emission surface 11 of the flat emitter 1.
- the main emission surface 11 is in the 3 and 4 each shown an embodiment.
- the main emission surface 11 has a planar structure 12 with a one-piece frame 13. Within the frame 13, a structure 12 is arranged, by which the main emission surface 11 is divided into segments 14a to 14f. In this way, a freely selectable number of segments 14a to 14f can be heated in a defined manner by the heat emission surface 21 (shown in dashed lines) of the field effect electron emitter 2, whereby the emission of thermal electrons from the main emission surface 11 is purposefully improved.
- the main emission surface 11 according to FIG. 4 also has a planar structure 15 which consists of elastic elements 16.
- the elastic elements 16 are arranged in a two-part frame 17, wherein the larger proportion of the elastic elements 16 over the Schuemissions Solution 21 (shown in dashed lines) of the field effect electron emitter 2 is arranged and the smaller proportion of the elastic elements 16 for mechanical temperature compensation.
- the field effect emitter segments 22 of the field effect electron emitter 2 By applying voltages to the field effect emitter segments 22 of the field effect electron emitter 2, an electric field builds up between the flat emitter 1 (which is at a uniform potential) and the field effect emitter segments 22 of the field effect electron emitter 2. As a result, the power registered in the field effect electron emitter 2 can be regulated individually for each field effect emitter segment 22. As a result, the emission distribution of the flat emitter 1 can be controlled in a simple manner. This allows e.g. an asymmetrical focal spot distribution or an emission distribution optimization, which improves the modulation transfer functions (MTF) and thus the image quality.
- MTF modulation transfer functions
Abstract
Die Erfindung betrifft eine thermionische Emissionsvorrichtung, umfassend
- einen Flachemitter (1) mit einer Hauptemissionsfläche (11), der an ein Hauptpotential (U1) schaltbar ist, und
- einen zuschaltbaren Feldeffekt-Elektronenemitter (2) mit einer Heizemissionsfläche (21), die an ein Heizpotential (U2) schaltbar ist, das unterschiedlich zum Hauptpotential (U1) ist.The invention relates to a thermionic emission device comprising
- A flat emitter (1) having a main emission surface (11), which is switchable to a main potential (U 1 ), and
- A switchable field effect electron emitter (2) with a Heizemissionsfläche (21), which is switchable to a heating potential (U 2 ), which is different from the main potential (U 1 ).
Eine derartige thermionische Emissionsvorrichtung besitzt eine längere Lebensdauer bei gleichbleibender Bildqualität. Such a thermionic emission device has a longer life with the same image quality.
Description
Die Erfindung betrifft eine thermionische Emissionsvorrichtung.The invention relates to a thermionic emission device.
Eine derartige thermionische Emissionsvorrichtung ist z.B. aus der
Unter einer unstrukturierten Emissionsfläche wird eine flache, im Wesentlichen homogene Emissionsfläche ohne Schlitze oder ähnliche Unterbrechungen verstanden. Eine Emissionsfläche, die beispielsweise durch Schlitze unterbrochen ist oder eine mäanderförmige Leiterbahn aufweist, wird als strukturiert bezeichnet.An unstructured emission surface is understood to mean a flat, substantially homogeneous emission surface without slits or similar interruptions. An emission surface, which is interrupted for example by slots or has a meander-shaped conductor track, is referred to as structured.
Bei der aus der
Der in der thermionische Emissionsvorrichtung erzeugte Elektronenstrahl trifft in einem Brennfleck auf eine Drehanode auf. Aufgrund des Brennfleckprofils des Elektronenstrahls entsteht auf der Brennbahn eine Oberflächentemperatur von bis zu 2.400 °C. Diese Oberflächentemperatur der Brennbahn kann ohne unerwünschte Verkürzung der Lebensdauer der Drehanode nicht erhöht werden, so dass allenfalls nur eine sehr geringe Leistungserhöhung über einen sehr kurzen Zeitraum und einer anschließenden Abkühlphase realisierbar ist.The electron beam generated in the thermionic emission device impinges on a rotary anode in a focal spot. Due to the focal spot profile of the electron beam, a surface temperature of up to 2,400 ° C is generated on the focal track. This surface temperature of the focal track can not be increased without undesirable shortening of the life of the rotary anode, so that only a very small increase in power over a very short period of time and a subsequent cooling phase can be realized.
Weitere indirekte Heizungen für thermionische Emitter sind in der
In der
Aus der
Die
Weiterhin ist aus der
Eine asymmetrische Emission von Elektronen ist z.B. aus der
In der
Aufgabe der vorliegenden Erfindung ist es, eine thermionische Emissionsvorrichtung für eine Röntgenröhre zu schaffen, die bei gleichbleibender Bildqualität eine längere Lebensdauer der Röntgenröhre gewährleistet.Object of the present invention is to provide a thermionic emission device for an X-ray tube, which ensures a longer life of the X-ray tube with the same image quality.
Die Aufgabe wird erfindungsgemäß durch eine thermionische Emissionsvorrichtung gemäß Anspruch 1 gelöst. Vorteilhafte Ausgestaltungen der Erfindung sind jeweils Gegenstand von weiteren Ansprüchen.The object is achieved by a thermionic emission device according to
Die thermionische Emissionsvorrichtung nach Anspruch 1 umfasst einen Flachemitter mit einer Hauptemissionsfläche, der an ein Hauptpotential schaltbar ist, sowie einen zuschaltbaren Feldeffekt-Elektronenemitter mit einer Heizemissionsfläche, die an ein Heizpotential schaltbar ist, das unterschiedlich zum Hauptpotential ist.The thermionic emission device of
Bei der erfindungsgemäßen Emissionsvorrichtung wird die Hauptemissionsfläche des Flachemitters durch Elektronen aufgeheizt, die von der Heizemissionsfläche des Feldeffekt-Elektronenemitters emittiert werden. Der Feldeffekt-Elektronenemitter bildet somit eine indirekte Heizung für den Flachemitter.In the emission device of the present invention, the main emission surface of the flat emitter is heated by electrons emitted from the heating emission surface of the field effect electron emitter. The field effect electron emitter thus forms an indirect heater for the flat emitter.
Dadurch, dass bei dem Feldeffekt-Elektronenemitter eine kalte Emission der Elektronen erfolgt, ist das Heizpotential das die Emission der Elektronen aus der Heizemissionsfläche bewirkt, unterschiedlich zum Hauptpotential, das zu der thermischen Emission der Elektronen aus der Hauptemissionsfläche des Flachemitters führt.By performing a cold emission of the electrons in the field effect electron emitter, the heating potential causing the emission of the electrons from the heating emission surface is different from the main potential resulting in the thermal emission of the electrons from the main emission surface of the flat emitter.
Aufgrund der kalten Elektronenemission ist im Stand-by-Betrieb deshalb auch keine thermische Heizung des Elektronenemitters erforderlich, wodurch sich eine längere Lebensdauer für die thermionische Emissionsvorrichtung nach Anspruch 1 ergibt.Due to the cold electron emission, therefore, no thermal heating of the electron emitter is required in stand-by mode, resulting in a longer life for the thermionic emission device according to
Im Rahmen der Erfindung können die Feldeffekt-Elektronenemitter beispielsweise als CNT-basierte Feldemittern (CNT, Carbon Nano Tubes, Kohlenstoff-Nanoröhren) oder als Si-basierte Feldemitter (Si, Silizium) ausgeführt sein. Auch nanokristalliner Diamant ist gemäß der
Vorzugsweise sind die Hauptemissionsfläche und die Heizemissionsfläche strukturiert (Anspruch 2). Diese Strukturierung ist bei einem Flachemitter mit rechteckiger Oberfläche beispielsweise durch Schlitze auf der Hauptemissionsfläche realisierbar Auf der Heizemissionsfläche ist diese Strukturierung z.B. durch eine entsprechende Segmentierung des Feldeffektemittermaterials realisierbar. Durch eine derartige Strukturierung erhält man auf einfache Weise einen definierten Brennfleck.Preferably, the main emission surface and the heating emission surface are structured (claim 2). This structuring can be realized in the case of a flat emitter with a rectangular surface, for example by means of slots on the main emission surface. On the heating emissive surface, this structuring is e.g. can be realized by a corresponding segmentation of the field effect emitter material. By such structuring, a defined focal spot is easily obtained.
Gemäß einer besonders vorteilhaften Ausführungsform der thermionischen Emissionsvorrichtung weist die Heizemissionsfläche zu der Hauptemissionsfläche einen vorgebbaren Abstand auf (Anspruch 3). Bei CNT-basierten Feldemittern (CNT, Carbon Nano Tubes, Kohlenstoff-Nanoröhren) liegt der vorgebbare Abstand zwischen Heizemissionsfläche und Hauptemissionsfläche beispielsweise zwischen ca. 0,5 mm und 5 mm. Anstelle von CNT-basierten Feldemittern sind auch Si-basierte Feldemitter (Si, Silizium) einsetzbar. Auch die Verwendung von wenigstens zwei verschiedenen Feldemissions-Materialien ist Rahmen der Erfindung möglich.According to a particularly advantageous embodiment of the thermionic emission device, the heating emission surface to the main emission surface has a predeterminable distance (claim 3). In the case of CNT-based field emitters (CNT, carbon nanotubes, carbon nanotubes), the predeterminable distance between the heating emission surface and the main emission surface is, for example, between approximately 0.5 mm and 5 mm. Instead of CNT-based field emitters, Si-based field emitters (Si, silicon) can also be used. The use of at least two different field emission materials is also possible within the scope of the invention.
Die Hauptemissionsfläche der thermionischen Emissionsvorrichtung ist in vorteilhafter Weise durch die Heizemissionsfläche in einem vorgebbaren Bereich aufheizbar (Anspruch 4). Die Heizemissionsfläche der thermionischen Emissionsvorrichtung umfasst hierzu eine vorgebbare Anzahl von einzeln ansteuerbaren Feldeffekt-Emittersegmenten (Anspruch 5).The main emission surface of the thermionic emission device can advantageously be heated by the heating emission surface in a predeterminable range (claim 4). The heating emission surface of the thermionic emission device for this purpose comprises a predeterminable number of individually controllable field effect emitter segments (claim 5).
Die thermionische Emissionsvorrichtung gemäß der Erfindung bzw. deren vorteilhafte Ausgestaltungen (Ansprüche 2 bis 5) sind für den Einbau in einen Fokuskopf geeignet (Anspruch 6).The thermionic emission device according to the invention or its advantageous embodiments (claims 2 to 5) are suitable for installation in a focus head (claim 6).
Mit der thermionischen Emissionsvorrichtung (Ansprüche 1 bis 5) bzw. mit einem damit ausgestatteten Fokuskopf (Anspruch 6) ist auf einfache Weise eine Röntgenröhre mit einer deutlich verbesserten Dosismodulation herstellbar (Ansprüche 7 bis 9).With the thermionic emission device (claims 1 to 5) or with a focus head equipped therewith (claim 6), an X-ray tube with a significantly improved dose modulation can be produced in a simple manner (claims 7 to 9).
Durch die kurzen Abkühlzeiten beim Abschalten des Heizemitters sowie die deutlich kürzeren Abkühlzeiten des Hauptemitters bei abgeschaltetem Heizemitter, werden die Strahlenbelastungen entsprechend reduziert und die Aufnahmezeiten bei der Bildgebung verkürzt.Due to the short cooling times when switching off the heating emitter and the significantly shorter cooling times of the main emitter with switched off heater emitter, the radiation exposure is reduced accordingly and the recording times are shortened in the imaging.
Die vorstehend beschriebenen Röntgenröhren (Ansprüche 7 und 8) können ohne Modifikationen in das Strahlergehäuse eines Röntgenstrahlers eingebaut werden (Anspruch 9).The above-described X-ray tubes (claims 7 and 8) can be installed without modifications in the radiator housing of an X-ray source (claim 9).
Nachfolgend wird ein schematisch dargestelltes Ausführungsbeispiele der Erfindung anhand der Zeichnung näher erläutert, ohne jedoch darauf beschränkt zu sein. Es zeigen:
- FIG 1
- einen Längsschnitt durch eine Ausführungsform einer thermionischen Emissionsvorrichtung,
- FIG 2
- eine perspektivische Ansicht der thermionischen Emissionsvorrichtung entlang der Linie II-II in
FIG 1 , - FIG 3
- ein erstes Ausführungsbeispiel für eine strukturierte Hauptemissionsfläche eines Flachemitters in Draufsicht und
- FIG 4
- ein zweites Ausführungsbeispiel für eine strukturierte Hauptemissionsfläche eines Flachemitters in perspektivischer Ansicht.
- FIG. 1
- a longitudinal section through an embodiment of a thermionic emission device,
- FIG. 2
- a perspective view of the thermionic emission device along the line II-II in
FIG. 1 . - FIG. 3
- a first embodiment of a structured main emission surface of a flat emitter in plan view and
- FIG. 4
- A second embodiment of a structured main emission surface of a flat emitter in a perspective view.
Die in
Der Flachemitter 1 ist an ein Hauptpotential U1 schaltbar und der Feldeffekt-Elektronenemitter 2 ist an ein Heizpotential U2 schaltbar, das unterschiedlich zum Hauptpotential U1 ist.The
Der Heizemissionsfläche 21 des Feldeffekt-Elektronenemitters 2 umfasst eine vorgebbare Anzahl von Segmenten 22, die beispielsweises durch eine Metallisierung auf einem Substrat 23 aufgebracht sind. Die Strukturierung der Heizemissionsfläche 21 wird im gezeigten Ausführungsbeispiel durch die einzeln ansteuerbaren Feldeffekt-Emittersegmente 22 erreicht.The
Bei dem in
Die Heizemissionsfläche 21 weist zu der Hauptemissionsfläche 11 einen vorgebbaren Abstand 3 auf. Hierzu ist im Randbereich des Substrats 23 wenigstens ein Abstandshalter 4 angeordnet, durch den der Abstand 3 zwischen Heizemissionsfläche 21 und Hauptemissionsfläche 11 sichergestellt ist. Im dargestellten Ausführungsbeispiel ist gemäß
Aufgrund der Strukturierung der Heizemissionsfläche 21 ist die Hauptemissionsfläche 11 in einem vorgebbaren Flächenbereich definiert aufheizbar.Due to the structuring of the
Bei dem in
Die Hauptemissionsfläche 11 gemäß
Die Hauptemissionsfläche 11 gemäß
Durch das Anlegen von Spannungen an die Feldeffekt-Emittersegmente 22 des Feldeffekt-Elektronenemitters 2 baut sich ein elektrisches Feld zwischen dem (auf einem einheitlichen Potential liegenden) Flachemitter 1 und den Feldeffekt-Emittersegmenten 22 des Feldeffekt-Elektronenemitters 2 auf. Dadurch kann die in die in den Feldeffekt-Elektronenemitter 2 eingetragene Leistung für jedes Feldeffekt-Emittersegment 22 einzeln geregelt werden. Dies führt dazu, dass die Emissionsverteilung des Flachemitters 1 auf einfache Weise steuerbar ist. Dies erlaubt z.B. eine asymmetrische Brennfleckverteilung oder eine Optimierung der Emissionsverteilung, wodurch die Modulationstransferfunktionen (MTF) und damit die Bildqualität verbessert werden.By applying voltages to the field
Claims (9)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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EP18154147.5A EP3518266A1 (en) | 2018-01-30 | 2018-01-30 | Thermionic emission device |
PCT/EP2019/050387 WO2019149482A1 (en) | 2018-01-30 | 2019-01-09 | Emission device |
Applications Claiming Priority (1)
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EP18154147.5A EP3518266A1 (en) | 2018-01-30 | 2018-01-30 | Thermionic emission device |
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EP18154147.5A Withdrawn EP3518266A1 (en) | 2018-01-30 | 2018-01-30 | Thermionic emission device |
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WO (1) | WO2019149482A1 (en) |
Families Citing this family (2)
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DE102020206939B4 (en) * | 2020-06-03 | 2022-01-20 | Siemens Healthcare Gmbh | x-ray tube |
DE102020206938B4 (en) | 2020-06-03 | 2022-03-31 | Siemens Healthcare Gmbh | influencing a focal spot |
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