EP3226277A1 - Émetteur plat angulaire pour cathode de grande puissance avec commande d'émission électrostatique - Google Patents

Émetteur plat angulaire pour cathode de grande puissance avec commande d'émission électrostatique Download PDF

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Publication number
EP3226277A1
EP3226277A1 EP17162807.6A EP17162807A EP3226277A1 EP 3226277 A1 EP3226277 A1 EP 3226277A1 EP 17162807 A EP17162807 A EP 17162807A EP 3226277 A1 EP3226277 A1 EP 3226277A1
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EP
European Patent Office
Prior art keywords
electron beam
emitters
focusing
cathode assembly
target
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.)
Pending
Application number
EP17162807.6A
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German (de)
English (en)
Inventor
Sergio Lemaitre
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General Electric Co
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General Electric Co
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Publication date
Priority claimed from US15/086,257 external-priority patent/US10468222B2/en
Application filed by General Electric Co filed Critical General Electric Co
Publication of EP3226277A1 publication Critical patent/EP3226277A1/fr
Pending legal-status Critical Current

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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
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • 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

  • Embodiments of the invention relate generally to X-ray tubes and more particularly to an apparatus for improved focusing control and increased useful life of the tube.
  • an X-ray source emits a fan-shaped beam or a cone-shaped beam towards a subject or an object, such as a patient or a piece of luggage.
  • the beam after being attenuated by the subject, impinges upon an array of radiation detectors.
  • the intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the X-ray beam by the subject.
  • Each detector element of a detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element.
  • the electrical signals are transmitted to a data processing system for analysis.
  • the data processing system processes the electrical signals to facilitate generation of an image.
  • the X-ray source and the detector array are rotated about a gantry within an imaging plane and around the subject.
  • the X-ray source generally includes an X-ray tube, which emits the X-ray beam at a focal point.
  • the X-ray detector or detector array typically includes a collimator for collimating X-ray beams received at the detector, a scintillator disposed adjacent to the collimator for converting X-rays to light energy, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
  • X-ray tubes employed in CT systems fail to control the level of electron beam intensity to a desired temporal resolution.
  • microwave sources include an electron gun that includes a focusing electrode, such as a Pierce electrode to generate an electron beam.
  • These electron guns typically include a grid to control a beam current magnitude via use of control grid means.
  • the energy and duty cycle of the electron beam makes the introduction of an intercepting wire mesh grid difficult since the thermo-mechanical stresses in the grid wires are reduced when the intercepted area of the electron beam is minimized.
  • rapidly changing the electron beam current prevents proper positioning and focusing of the electron beam on the X-ray target. Modulation of the electron beam current from 0 percent to 100 percent of the electron beam intensity changes the forces in the electron beam, due to changes in the space charge force resulting in change in the desired electromagnetic focusing and deflection.
  • an X-ray tube includes a cathode assembly on which is disposed a pair of emission surfaces for generating a pair of electron beams, the pair of emission surfaces disposed at an angle with regard to one another.
  • an injector or cathode assembly for an X-ray tube includes a pair of emission surfaces that may be flat, curved, partially curved or any combination thereof that each emit streams of electrons from an that can combine to form an electron beam, at least one focusing electrode disposed around the emission surfaces, wherein the at least one focusing electrode focuses the electron beam and at least one extraction electrode that can be adjusted between a positive and negative bias with respect to the emission surfaces, wherein the at least one extraction electrode controls an intensity of the electron beam.
  • the pair of emission surfaces can be formed as a pair of emitters that may be flat, curved, partially curved or any combination thereof and that provide a large emission surface/emitter area that can accommodate large emission currents with an extended emitter lifespan.
  • the angled position of the emission surfaces/emitters in the cathode assembly or injector enables the electron beams emitted by each emission surface/emitter to provide an initial convergence of the beams to overcome the space charge of the electrons in the respective beams. This, in turn enables the waist of the converging electron beams to be positioned at a location in front of a magnetic focusing assembly at large and small emission currents, thereby enabling the magnetic focusing assembly to effectively affect/focus and direct the electron beam onto the desired focal spot. Further, by maintaining the position of the beam waist upstream or in front of the magnetic focusing assembly, the energy or current needed to be supplied to the magnetic focusing assembly to focus the electron beam is within normal ranges.
  • an X-ray tube in accordance with another exemplary aspect of the invention, includes an injector including a pair of emitters to emit an electron beam singly or in combination with one another, at least one focusing electrode disposed around the emitter, wherein the at least one focusing electrode focuses the electron beam and at least one extraction electrode for controlling an intensity of the electron beam, wherein the at least one extraction electrode can be adjusted between a positive and negative bias voltage with respect to the emitters.
  • the X-ray tube also includes a target for generating X-rays when impinged upon by the electron beam and a magnetic assembly located between the injector and the target for directionally influencing focusing, deflecting and/or positioning the electron beam towards the target.
  • a computed tomography system includes a gantry and an X-ray tube coupled to the gantry.
  • the X-ray tube includes a tube casing and an injector including a pair of emitters to emit an electron beam, at least one focusing electrode disposed around the emitters, wherein the at least one focusing electrode focuses the electron beam and at least one extraction electrode for controlling an intensity of the electron beam, wherein the at least one extraction electrode can be adjusted between a positive and negative bias with respect to the emitters.
  • the X-ray tube also includes a target for generating X-rays when impinged upon by the electron beam and a magnetic assembly located between the injector and the target for directionally influencing focusing deflecting and/or positioning the electron beam towards the target.
  • the computed tomography system includes an X-ray controller for providing power and timing signals to the X-ray tube and one or more detector elements for detecting attenuated X-ray beam from an imaging object.
  • X-ray tube including a cathode assembly on which is disposed a pair of emission surfaces for generating a pair of electron beams, the pair of emission surfaces disposed at an angle with regard to one another, a focusing electrode adjacent the cathode assembly for focusing the electron beams, an extraction electrode spaced from the focusing electrode opposite the cathode assembly for controlling the intensity of the electron beam by adjusting a positive or negative voltage applied to the extraction electrode, a magnetic assembly spaced from the extraction electrode opposite the focusing electrode and a target spaced from the magnetic assembly opposite the extraction electrode.
  • a cathode assembly includes an emitter having a first emission surface configured to emit a first electron beam therefrom and a second emission surface disposed on the cathode assembly and configured to emit a second electron beam therefrom, wherein the first emission surface and the second emission surface are disposed at an angle with regard to one another.
  • a method for focusing an electron beam emitted from an X-ray tube includes the steps of providing an X-ray tube including a cathode assembly on which is disposed a pair of emission surfaces for generating a pair of electron beams, the pair of emission surfaces disposed at an angle with regard to one another, a focusing electrode adjacent the cathode assembly, an extraction electrode spaced from the focusing electrode opposite the cathode assembly that can be can be adjusted between a positive and negative bias relative to the pair of emission surfaces, a magnetic assembly spaced from the extraction electrode opposite the focusing electrode and a target spaced from the magnetic assembly opposite the extraction electrode capable of generating X-rays when impinged upon by the electron beams, passing an emission current through at least one of the pair of emission surfaces to generate an electron beam; and passing a focusing current through the magnetic assembly to focus the electron beam onto the target.
  • a computed tomography system includes a gantry, an X-ray tube coupled to the gantry, the X-ray tube including a cathode assembly having a pair of emission surfaces for generating an electron beam, the pair of emission surfaces disposed therein at angles with respect to one another, a focusing electrode for focusing the electron beam; an extraction electrode which controls the intensity of the electron beam though the adjustment of a positive or negative biasing voltage applied to the extraction electrode; a target for generating X-rays when impinged upon by the electron beam, a magnetic assembly located between the cathode assembly and the target for focusing the electron beam towards the target, an X-ray controller for providing power and timing signals to the X-ray tube and one or more detector elements for detecting attenuated X-ray beam from an imaging object.
  • Exemplary embodiments of the invention relate to an X-ray tube including an increased emitter area to accommodate larger emission currents in conjunction with microsecond X-ray intensity switching in the X-ray tube.
  • An exemplary X-ray tube and a computed tomography system employing the exemplary X-ray tube are presented.
  • a computed tomography (CT) imaging system 10 is illustrated in accordance with one exemplary embodiment of the invention, such as that disclosed in co-owned US Patent No. 8,401,151 , entitled “X-Ray Tube For Microsecond X-Ray Intensity Switching", the entirety of which is expressly incorporated by reference herein for all purposes.
  • the CT imaging system 10 includes a gantry 12.
  • the gantry 12 has an X-ray source 14, which typically is an X-ray tube that projects a beam of X-rays 16 towards a detector array 18 positioned opposite the X-ray tube on the gantry 12.
  • the gantry 12 may have multiple X-ray sources (along the patient theta or patient Z axis) that project beams of X-rays.
  • the detector array 18 is formed by a plurality of detectors 20 which together sense the projected X-rays that pass through an object to be imaged, such as a patient 22.
  • the gantry 12 and the components mounted thereon rotate about a center of rotation 24.
  • the CT imaging system 10 described with reference to the medical patient 22 it should be appreciated that the CT imaging system 10 may have applications outside the medical realm.
  • the CT imaging system 10 may be utilized for ascertaining the contents of closed articles, such as luggage, packages, etc., and in search of contraband such as explosives and/or biohazardous materials.
  • the control mechanism 26 includes an X-ray controller 28 that provides power and timing signals to the X-ray source 14 and a gantry motor controller 30 that controls the rotational speed and position of the gantry 12.
  • a data acquisition system (DAS) 32 in the control mechanism 26 samples analog data from the detectors 20 and converts the data to digital signals for subsequent processing.
  • An image reconstructor 34 receives sampled and digitized X-ray data from the DAS 32 and performs high-speed reconstruction. The reconstructed image is applied as an input to a computer 36, which stores the image in a mass storage device 38.
  • DAS data acquisition system
  • the computer 36 also receives commands and scanning parameters from an operator via operator console 40 that may have an input device such as a keyboard (not shown in FIGS. 1-2 ).
  • An associated display 42 allows the operator to observe the reconstructed image and other data from the computer 36.
  • Commands and parameters supplied by the operator are used by the computer 36 to provide control and signal information to the DAS 32, the X-ray controller 28 and the gantry motor controller 30.
  • the computer 36 operates a table motor controller 44, which controls a motorized table 46 to position the patient 22 and the gantry 12. Particularly, the table 46 moves portions of patient 22 through a gantry opening 48.
  • the computer 36 may operate a conveyor system controller 44, which controls a conveyor system 46 to position an object, such as, baggage or luggage and the gantry 12. More particularly, the conveyor system 46 moves the object through the gantry opening 48.
  • the X-ray source 14 is typically an X-ray tube that includes at least a cathode and an anode.
  • the cathode may be a directly heated cathode or an indirectly heated cathode.
  • X-ray tubes include an electron source to generate an electron beam and impinge the electron beam on the anode to produce X-rays. These electron sources control a beam current magnitude by changing the current on the filament, and therefore emission temperature of the filament.
  • these X-ray tubes fail to control electron beam intensity to a view-to-view basis based on scanning requirements, thereby limiting the system imaging options.
  • an exemplary X-ray tube where the X-ray tube provides microsecond current control during nominal operation, on/off gridding for gating or usage of multiple X-ray sources, 0 percent to 100 percent modulation for improved X-ray images, and dose control or fast voltage switching for generating X-rays of desired intensity resulting in enhanced image quality.
  • FIG. 3 is a diagrammatical illustration of an exemplary X-ray tube 50, in accordance with aspects of the present technique.
  • the X-ray tube 50 may be the X-ray source 14 (see FIGS. 1-2 ).
  • the X-ray tube 50 includes an exemplary injector or cathode assembly 52 disposed within a vacuum wall 54.
  • the injector 52 includes an injector wall 53 that encloses various components of the injector 52.
  • the X-ray tube 50 also includes an anode 56.
  • the anode 56 is typically an X-ray target.
  • the injector 52 and the anode 56 are disposed within a tube casing 72.
  • the injector 52 may include at least one cathode in the form of a pair of emitters 58.
  • the cathode, and in particular the emitters 58 may be directly heated.
  • the emitters 58 may be coupled to an emitter support/cathode cup 60, and the emitter support/cathode cup 60 in turn may be coupled to the injector wall 53.
  • the emitters 58 may be heated by passing a large current through the emitters 58.
  • a voltage source 66 may supply this current to the emitters 58. In one embodiment, a current of about 10 amps (A) may be passed through the emitters 58.
  • the emitters 58 may emit an electron beam 64 as a result of being heated by the current supplied by the voltage source 66.
  • the term "electron beam" may be used to refer to a stream of electrons that have substantially similar velocities.
  • the electron beam 64 may be directed towards the target 56 to produce X-rays 84. More particularly, the electron beam 64 may be accelerated from the emitters 58 towards the target 56 by applying a potential difference between the emitters 58 and the target 56.
  • a high voltage in a range from about 40 kV to about 450 kV may be applied via use of a high voltage feedthrough 68 to set up a potential difference between the emitters 58 and the target 56, thereby generating a high voltage main electric field 78.
  • a high voltage differential of about 140 kV may be applied between the emitters 58 and the target 56 to accelerate the electrons in the electron beam 64 towards the target 56.
  • the target 56 may be at ground potential.
  • the emitters 58 may be at a potential of about -140 kV and the target 56 may be at ground potential or about zero volts.
  • emitters 58 may be maintained at ground potential and the target 56 may be maintained at a positive potential with respect to the emitters 58.
  • the target may be at a potential of about 140 kV and the emitters 58 may be at ground potential or about zero volts.
  • the emitters 58 can have a potential of -70kV while the target 56 has a potential of +70kV.
  • a rotating target may be used to circumvent the problem of heat generation in the target 56. More particularly, in one embodiment, the target 56 may be configured to rotate such that the electron beam 64 striking the target 56 does not cause the target 56 to melt since the electron beam 64 does not strike the target 56 at the same location. In another embodiment, the target 56 may include a stationary target. Furthermore, the target 56 may be made of a material that is capable of withstanding the heat generated by the impact of the electron beam 64. For example, the target 56 may include materials such as, but not limited to, tungsten, molybdenum, or copper.
  • the injector/cathode assembly 52 may include at least one focusing electrode 70 within a shield 71.
  • the at least one focusing electrode 70 may be disposed adjacent to the emitters 58 such that the focusing electrode 70 focuses the electron beam 64 towards the target 56.
  • the term "adjacent" means near to in space or position.
  • the focusing electrode 70 may be maintained at a voltage potential that is less than a voltage potential of the emitters 58. The potential difference between the emitters 58 and focusing electrode 70 prevents electrons generated from the emitters 58 from moving towards the focusing electrode 70.
  • the focusing electrode 70 may be maintained at a negative potential with respect to that of the emitters 58.
  • the negative potential of the focusing electrode 70 with respect to the emitters 58 focuses the electron beam 64 away from the focusing electrode 70 and thereby facilitates focusing of the electron beam 64 towards the target 56.
  • the focusing electrode 70 may be maintained at a voltage potential that is equal to or substantially similar to the voltage potential of the emitter 58.
  • the similar voltage potential of the focusing electrode 70 with respect to the voltage potential of the emitters 58 creates a parallel electron beam by shaping electrostatic fields due to the shape of the focusing electrode 70.
  • the focusing electrode 70 may be maintained at a voltage potential that is equal to or substantially similar to the voltage potential of the emitters 58 via use of a lead (not shown in FIG. 3 ) that couples the emitters 58 and the focusing electrode 70.
  • the injector 52 includes at least one extraction electrode 74 positioned on and electrically insulated from the emitters 58 and the focusing electrode 70 by a support/insulation 106 ( FIGS. 7 ) for additionally controlling and focusing the electron beam 64 towards the target 56.
  • the at least one extraction electrode 74 is located between the target 56 and the emitters 58.
  • the extraction electrode 74 may be positively biased via use of a voltage tab (not shown in FIG. 3 ) for supplying a desired voltage to the extraction electrode 74.
  • a bias voltage power supply 90 may supply a voltage to the extraction electrode 74 such that the extraction electrode 74 is maintained at a positive bias voltage with respect to the emitters 58.
  • the extraction electrode 74 may be divided into a plurality of regions having different voltage potentials to perform focusing or a biased emission from different regions of the emitters 58.
  • energy of an X-ray beam may be controlled via one or more of multiple ways.
  • the energy of an X-ray beam may be controlled by altering the potential difference (that is acceleration voltage) between the cathode and the anode, or by changing the material of the X-ray target, or by filtering the electron beam.
  • kV control the term “electron beam current” refers to the flow of electrons per second between the cathode and the anode.
  • an intensity of the X-ray beam is controllable via control of the electron beam current.
  • Such a technique of controlling the intensity is generally referred to as "mA control.”
  • aspects of the present technique provide for control of the electron beam current via use of the extraction electrode 74, or electrostatic mA control. It may be noted that, the use of such extraction electrode 74 enables a decoupling of the control of electron emission from the acceleration voltage.
  • the extraction electrode 74 is configured for microsecond current control. Specifically, the electron beam current may be controlled in the order of microseconds by altering the voltage applied to the extraction electrode 74 in the order of microseconds. It may be noted that the emitters 58 may be treated as an infinite source of electrons. In accordance with aspects of the present technique, electron beam current, which is typically a flow of electrons from the emitters 58 towards the target 56, may be controlled by altering the voltage potential of the extraction electrode 74. Control of the electron beam current will be described in greater detail hereinafter.
  • the extraction electrode 74 may also be biased at a positive voltage with respect to the focusing electrode 70.
  • the voltage potential of emitters 58 is about -140 kV
  • the voltage potential of the focusing electrode 70 may be maintained at about -140 kV or less
  • the voltage potential of the extraction electrode 74 may be maintained at about -135 kV for positively biasing the extraction electrode 74 with respect to the emitters 58.
  • an electric field 76 is generated between the extraction electrode 74 and the focusing electrode 70 due to a potential difference between the focusing electrode 70 and the extraction electrode 74.
  • the strength of the electric field 76 thus generated may be employed to control the intensity of electron beam 64 generated by the emitters 58 towards the target 56.
  • the intensity of the electron beam 64 striking the target 56 may thus be controlled by the electric field 76. More particularly, the electric field 76 causes the electrons emitted from the emitters 58 to be accelerated towards the target 56.
  • the weaker the electric field 76 the lesser is the acceleration of electrons from the emitters 58 towards the target 56.
  • altering the bias voltage on the extraction electrode 74 may modify the intensity of the electron beam 64.
  • the bias voltage on the extraction electrode may be altered via use of the voltage tab present on the bias voltage power supply 90. Biasing the extraction electrode 74 more positively with respect to the emitter 58 results in increasing the intensity of the electron beam 64. Alternatively, biasing the extraction electrode 74 less positively or negatively with respect to the emitters 58 causes a decrease in the intensity of the electron beam 64.
  • thermoionic electron emitter the flat emitters, 100,102
  • the electron emission originating from the surface of a thermoionic electron emitter, the flat emitters, 100,102 strongly depends on the "pulling" electric field generated by the X-ray tube's anode 56.
  • X-ray tubes of the rotary-anode type may be equipped with a grid electrode, e.g., the extraction electrode 74, placed in front of the electron emitters 100,102.
  • a bias voltage is applied to the grid electrode which generates a repelling field and is usually given by the absolute value of the potential difference between the electron emitter and the grid electrode.
  • the resulting electric field at the emitter surface is the sum of the grid and the anode generated field. If the total field is repelling on all locations on the electron emitter, electron emission is completely cut off.
  • the electron beam 64 may be shut-off entirely by biasing the extraction electrode 74 negatively with respect to the emitters 58,100,102, as opposed to a positive bias on the extraction electrode 74 which serves to extract or accelerate the electron beam 64 away from the emitters 100,102.
  • the positive or negative bias voltage on the extraction electrode 74 may be supplied via use of the bias voltage power supply 90.
  • the intensity of the electron beam 64 may be controlled from 0 percent to 100 percent of possible intensity by changing the bias voltage on the extraction electrode 74 via use of the extractor voltage tab 91 present in the bias voltage power supply 90.
  • the extraction electrode 74 controls emission from 0mA to max mA. At 0mA the extraction voltage is negative with respect to the emitters 58 (gridding). At max mA, the extractor voltage is positive. For intermediate mA the extractor voltage assumes intermediate values, that can be both positive and negative.
  • an AC current is applied to the emitters 58, 100,102 in order to create thermionic emission of electrons form the emitters 58,100,102 as a result of the Joule heating of the emitters 100,102.
  • the voltage supplied by the current to the emitters 100,102 varies with time can oscillate between being greater and less than the tube voltage, such as on the order of ⁇ 20V.
  • the focusing electrode 70, 107 disposed around the emitters 100,102 can be maintained at the tube voltage. The focusing electrode 70 focuses the electron beam 64, while the extraction electrode 74 controls the intensity of the electron beam 64, as discussed previously.
  • the extraction electrode 74 can be adjusted between a positive (extraction) or negative (gridding) bias voltage using extractor voltage tab 91 with respect to the emitters 100,102.
  • the circuit 90 provides a tube or accelerating voltage between the cathode 52/emitters 100,102 and the anode 54, 56 in order to direct and accelerate the electron beam produced by the emitters 100,102 through the extraction electrode 74 and towards the anode or target 54,56.
  • the voltage supplied to the extraction electrode 74 via the circuit 90 is varied to change the intensity of the electron beam 64 from the emitters 100,102.
  • the extraction electrode 74 functions to provide a repelling force on the electron beam from the emitters 100,102, thereby preventing passage of the electron beam through the extraction electrode 74, "gridding" the electron beam, and reducing the intensity of the electron beam to zero.
  • the voltage V grid is determined by the accelerating voltage applied between the cathode 52 and the anode 56, with a higher acceleration voltage consequently requiring a more negative V grid .
  • the intensity of the electron beam passing through the extraction electrode 74 can be adjusted, such as during an x-ray exposure, to place the extraction electrode 74 at a positive or negative bias relative to the emitters 100,102 in order to control the intensity of the electron beam in real-time.
  • voltage shifts of 20 kV or less may be applied to the extraction electrode 74 to control the intensity of the electron beam 64.
  • these voltage shifts may be applied to the extraction electrode 74 via use of a control electronics module 92.
  • the control electronics module 92 changes the voltage applied to the extraction electrode 74 in intervals of 1-15 microseconds to intervals of about at least 150 milliseconds.
  • the control electronics module 92 may include Si switching technology circuitry to change the voltage applied to the extraction electrode 74.
  • SiC silicon carbide
  • changes in voltage applied to the extraction electrode 74 facilitates changes in intensity of the electron beam 64 in intervals of 1-15 microseconds, for example.
  • This technique of controlling the intensity of the electron beam in the order of microseconds may be referred to as microsecond intensity switching.
  • the exemplary X-ray tube 50 may also include a magnetic assembly 80 for focusing and/or positioning and deflecting the electron beam 64 on the target 56.
  • the magnetic assembly 80 may be disposed between the injector 52 and the target 56, and in one exemplary embodiment at a distance of between 20-40mm from the anode or extraction electrode 74.
  • the magnetic assembly 80 may include one or more multipole magnets for influencing focusing of the electron beam 64 by creating a magnetic field that shapes the electron beam 64 on the X-ray target 56.
  • the one or more multipole magnets may include one or more quadrupole magnets, one or more dipole magnets, or combinations thereof.
  • the magnetic assembly 80 provides a magnetic field having a performance controllable from steady-state to a sub-30 microsecond time scale for a wide range of focal spot sizes. This provides protection of the X-ray source system, as well as achieving CT system performance requirements. Additionally, the magnetic assembly 80 may include one or more dipole magnets for deflection and positioning of the electron beam 64 at a desired location on the X-ray target 56. The electron beam 64 that has been focused and positioned impinges upon the target 56 to generate the X-rays 84.
  • the X-rays 84 generated by collision of the electron beam 64 with the target 56 may be directed from the X-ray tube 50 through an opening in the tube casing 72, which may be generally referred to as an X-ray window 86, towards an object (not shown in FIG. 3 ).
  • the exemplary X-ray tube 50 may include an electron collector 82 for collecting electrons that are backscattered from the target 56.
  • the electron collector 82 may be maintained at a ground potential.
  • the electron collector 82 may be maintained at a potential that is substantially similar to the potential of the target 56.
  • the electron collector 82 may be located adjacent to the target 56 to collect the electrons backscattered from the target 56.
  • the electron collector 82 may be located between the extraction electrode 74 and the target 56, close to the target 56.
  • the electron collector 82 may be formed from a refractory material, such as, but not limited to, molybdenum.
  • the electron collector 82 may be formed from copper.
  • the electron collector 82 may be formed from a combination of a refractory metal and copper.
  • the exemplary X-ray tube 50 may also include a positive ion collector (not shown in FIG. 3 ) to attract positive ions that may be produced due to collision of electrons in the electron beam 64 with the target 56.
  • the positive ion collector is generally placed along the electron beam path and prevents the positive ions from striking various components in the X-ray tube 50, thereby preventing damage to the components in the X-ray tube 50.
  • the emitters 58 are formed as a pair of flat emitters 100,102 disposed within the injector/cathode assembly 52 at an angle with respect to one another.
  • the injector/cathode assembly 52 is mounted to a high voltage insulator 104 disposed on an extender 105 ( FIG.
  • the emitters 100,102 are spaced from one another without any intervening structure or septum disposed between the emitters 100,102, enabling the beams of electrons emitted from each emitter 100,102 to interact with one another as they project outwardly from the emitters 100,102.
  • the emitters 100,102 can be spaced from one another any suitable distance, but in the exemplary illustrated embodiment are spaced from about 50 ⁇ m to about 500 ⁇ m. However, in an alternative exemplary embodiment, the emitters 100,102 can be formed from a single sheet of material that is bent or otherwise deformed along a centerline of the material to form the emitters 100,102 on each half of the material. The material containing the emitters 100,102 can subsequently be attached, e.g., welded or brazed, to the injector 52. Further, in either embodiment above, the emitters 100,102 can be the same or different sizes, and/or can be the same or different shapes. In any configuration, the emitters 100,102 are positioned at an angle with regard to one another, as shown in FIGS.
  • the emitters 100,102 are positioned on the injector 52 at angles from a horizontal, as defined by plane H in FIG. 13 , with the emitters 100,102 angled towards each other.
  • said angles range from about 1 degree to about 45 degrees or, in other exemplary embodiments, from about 2 degrees to about 20 degrees or, in other exemplary embodiments, from about 4 degrees to about 12 degrees.
  • only one of the emitters is positioned at an angle within one of the above ranges from the defined horizontal, where the other emitter is parallel to said horizontal.
  • both emitters 100,102 could be parallel to the defined horizontal, or at varying angles relative to said horizontal (i.e. both emitters can be positioned at the same angle relative to the defined horizontal, or the emitters can be positioned where one emitter is at one angle and the other emitter is at a different angle). Still further, the emitters 100,102 could be angled away from each other.
  • the emitters 100,102 are flat emitters, where the term "flat emitter” may be used to refer to an emitter that has a flat emission surface.
  • the emitters 100,102 may be curved emitters or emitters including a curved portion thereon, such as in the width direction of the emitters 100,102.
  • the curved emitter which is typically concave in curvature along the long axis of each emitter 100,102, provides fine tuning or pre-focusing of the electron beam 64 from each emitter 100,102.
  • the term "curved emitter” may be used to refer to the emitter that has a curved emission surface.
  • shaped emitters 100,102 may also be employed.
  • various polygonal shaped emitters 100,102 such as, a square emitter, or a rectangular emitter may be employed.
  • other such shaped emitters 100,102 such as, but not limited to elliptical or circular emitters may also be employed.
  • emitters 100,102 of different shapes or sizes may be employed based on the application requirements, including emitters 100,102 of different shapes or configurations.
  • the emitters 100,102 may be formed from a low work-function material. More particularly, the emitters 100,102 may be formed from a material that has a high melting point and is capable of stable electron emission at high temperatures.
  • the low work-function material may include materials such as, but not limited to, tungsten, thoriated tungsten, lanthanum hexaboride, and the like.
  • the emitters 100,102 can be formed in any desired manner of any desired material and configuration, such as that disclosed in co-pending and co-owned US Patent Application Serial No. 14/586,066 , entitled Low Aberration, High Intensity Electron Beam For X-Ray Tube, the entirety of which is expressly incorporated herein by reference for all purposes.
  • the emitters 100,102 each include an emission surface 100',102' that form the angled portion of the emitters 100,102 and that emits an electron beam 64 therefrom upon passage of a current through the emitters 100,102.
  • the emitters 100,102 and emission surfaces 100',102' can be formed as disclosed in co-pending and co-owned US Non-Provisional Patent Application Serial No. 15/085,419 , entitled Fabrication Methods And Modal Stiffening For Non-Flat Single / Multi-Piece Embitter, (the '419 application) the entirety of which is expressly incorporated herein by reference for all purposes.
  • Emission surfaces 100,102 may be formed to be electrically isolated from one another or wired in either wired in series or parallel.
  • the emitters 100,102 and/or emission surfaces 100',102' can be formed completely separately from one another, or can be formed to be connected to one another using a ligament 300 that extends between the emitters 100,102 and/or emission surfaces 100',102', such as between one end of each of the emitters 100,102 and/or emission surfaces 100',102'.
  • the emitters 100,102 and/or emission surfaces 100',102' can be formed to be connected by a substrate 302 on which the emitters 100,102 and/or emission surfaces 100',102' are placed, optionally in conjunction with a ligament 300
  • the shape of the current path along the emitters 100,102 and/or emission surfaces 100',102' can be formed as desired, such with a sinusoidal or switchback configuration, as shown in FIG. 13 , or in any other suitable or desired configuration, such as those shown in the '419 application and/or in co-pending and co-owned US Non-Provisional Patent Application Serial No. 15/086,257 , entitled Angled Flat Emitted For High Power Cathode With Electrostatic Emission Control, (the '257 application) the entirety of which is expressly incorporated herein by reference for all purposes.
  • one or both of the first emission surface 100' and the second emission surface 102' can be substantially planar, can follow a sinusoidal pathway, can be curved, can be are fitted to extend along portions of a continuous curved path, can be concave, or any combination thereof.
  • the emitters 100,102 and/or emission surfaces 100',102' are positioned adjacent one another in the cathode assembly 60 in order to form a first pair of emitters 100,102.
  • the cathode assembly 60 can include an additional or second pair of emitters 304,306 disposed within the cathode assembly 60 at locations spaced outwardly from the emitters 100,102 and/or emission surfaces 100',102'.
  • the second pair of emitters 304,306 can be formed similarly to the emitters 100,102, to operate similarly, and can be positioned at an angle relative to one another and to the horizontal plane H, such as at an angle within a range of 2 degrees to 20 degrees from horizontal, as defined by plane H.
  • the present invention contemplates that emitters 304 and 100, as well as emitters 305 and 102, respectively, may be coplanar or may be angled with respect to each other.
  • the electron beams 64 combine into a single beam 164.
  • the combined beam 164 converges at a point or waist 104 close to the cathode or focusing electrode 70 due to a low amount of space charge in the beam 164, i.e. internal repulsion in the beam 164 due to the interaction or repellence of the electrons in the beam 164.
  • the beam 164 when the beam 164 reaches the magnetic focusing assembly 80, which in the exemplary embodiment is formed of defocusing quadrupole magnet 81 and focusing quadrupole magnet 83, the beam 164 is expanding and can easily be focused onto the target 56 by the magnets 81,83.
  • the emission current applied to the emitters 100,102 is high, e.g., an emission current up to between 1-2A, due to the added space charge of the electron beam 164 as a result of the increased emission current, the beam waist 104 is moved more downstream away from the cathode or focusing electrode 70.
  • the angled geometry of the emitters 100,102 due to the angled geometry of the emitters 100,102, a larger total surface area of the emitters 100,102 can be realized that leads to reduced space charge.
  • the use of a curved emitter surface may be better, but there do not currently exist manufacturing methods to produce a curved surface, directly heated emitter.
  • indirectly heated curved surface emitters are a possibility, but at a significantly higher cost to the cathode and increased cathode control complexity.
  • the electron beam 64 launches in an orientation closer to a parallel beam. Furthermore, with the consequent added space charge of the electron beam 64, the beam waist 104 is moved more downstream from the cathode/focusing electrode 70.
  • the emission current is high enough, i.e., approximately between 0.6A-0.7A, the waist 104 is positioned within the magnet 81 of the assembly 80, rendering the magnet 81 very ineffective for focusing the beam 64 in the width plane without the use of excessively high magnet currents (e.g., 30-40A) in the assembly 80, and well above the current limits for the magnets 81,83.
  • FIGS. 11A which shows that the use of high emission currents, such as above about 0.5A, cause the discontinuity of the focusing range in an X-ray tube 50 including a non-angled emitter 58.
  • FIG. 11B the use of angled emitters 100,102 in an X-ray tube 50, such as those utilized in CT systems 10, shift the appearance of the discontinuity out to emission currents of approximately 1.5A, increasing the emission currents that can be utilized to increase the emission of the tube 12 without consequent increases in the temperature required for the emission, as required in prior art X-ray tubes.
  • the tube 50 will not degrade due to excessive heating thereby significantly extending the useful life of the tube 12 while maintaining focal spot size, and intensity and position of the electron beam 164 in the exemplary X-ray tube 50 resulting in improved image quality of the CT imaging system 10.

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EP17162807.6A 2016-03-31 2017-03-24 Émetteur plat angulaire pour cathode de grande puissance avec commande d'émission électrostatique Pending EP3226277A1 (fr)

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US15/086,257 US10468222B2 (en) 2016-03-31 2016-03-31 Angled flat emitter for high power cathode with electrostatic emission control
US201662425903P 2016-11-23 2016-11-23

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CN109119312A (zh) * 2018-09-30 2019-01-01 麦默真空技术无锡有限公司 一种磁扫描式的x射线管

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US3558967A (en) * 1969-06-16 1971-01-26 Varian Associates Linear beam tube with plural cathode beamlets providing a convergent electron stream
DE2727907A1 (de) * 1977-06-21 1979-01-18 Siemens Ag Roentgenroehren-gluehkathode
JP2005251502A (ja) * 2004-03-03 2005-09-15 Kobe Steel Ltd 電界電子放出装置
US7062017B1 (en) * 2000-08-15 2006-06-13 Varian Medical Syatems, Inc. Integral cathode
US20100183117A1 (en) * 2007-07-19 2010-07-22 Hitachi Medical Corporation X-ray generating apparatus and x-ray ct apparatus using the same
US20110188637A1 (en) * 2010-02-02 2011-08-04 General Electric Company X-ray cathode and method of manufacture thereof
US8401151B2 (en) 2009-12-16 2013-03-19 General Electric Company X-ray tube for microsecond X-ray intensity switching
JP2014229388A (ja) * 2013-05-20 2014-12-08 株式会社東芝 Ｘ線管

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3558967A (en) * 1969-06-16 1971-01-26 Varian Associates Linear beam tube with plural cathode beamlets providing a convergent electron stream
DE2727907A1 (de) * 1977-06-21 1979-01-18 Siemens Ag Roentgenroehren-gluehkathode
US7062017B1 (en) * 2000-08-15 2006-06-13 Varian Medical Syatems, Inc. Integral cathode
JP2005251502A (ja) * 2004-03-03 2005-09-15 Kobe Steel Ltd 電界電子放出装置
US20100183117A1 (en) * 2007-07-19 2010-07-22 Hitachi Medical Corporation X-ray generating apparatus and x-ray ct apparatus using the same
US8401151B2 (en) 2009-12-16 2013-03-19 General Electric Company X-ray tube for microsecond X-ray intensity switching
US20110188637A1 (en) * 2010-02-02 2011-08-04 General Electric Company X-ray cathode and method of manufacture thereof
JP2014229388A (ja) * 2013-05-20 2014-12-08 株式会社東芝 Ｘ線管

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Publication number Priority date Publication date Assignee Title
CN109119312A (zh) * 2018-09-30 2019-01-01 麦默真空技术无锡有限公司 一种磁扫描式的x射线管

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