X-ray source with liquid-cooled source coil

Abstract

To remove all unwanted heat from a source coil.SOLUTION: An electron beam B is typically dynamically steered on its path to a target 500 after generation. The steering is performed by one or more source coils 132N and 132S. These coils create a magnetic field outside a vacuum vessel 112 and allow air / water / oil cooling to remove unwanted heat. The magnetic field is then picked up within the vacuum vessel with a pole piece and directed toward a region where the magnetic field is needed to steer the electron beam.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Related Applications This application is related to U.S. Patent Application No. 17 / 238,799, Attorney Docket No. 0002.0086US1 (2020ID00442), now U.S. Patent Application Publication No. _, filed on the same date as this specification, entitled "Method and system for liquid cooling isolated X-ray transmission target", invented by Claus Flachenecker, Bruce Borchers, and Thomas A. Case, and U.S. Patent Application No. 17 / 238,811, Attorney Docket No. 0002.0087US1 (2020ID00446), now U.S. Patent Application Publication No. _, filed on the same date as this specification, entitled "Fiber-optic communication for embedded electronics in x-ray generator", invented by Claus Flachenecker.

[0002] All of the foregoing applications are hereby incorporated by reference in their entirety.

Background Art

[0003] Background Art X-rays are widely used in microscopy due to their short wavelength and ability to penetrate objects. Typically, the best sources of X-rays are synchrotrons, but these are expensive systems. Therefore, so-called tube or laboratory X-ray sources where a generated electron beam collides with a target are often used. The resulting X-rays include characteristic lines determined by the composition of the target and extensive bremsstrahlung.

[0004] X-ray microscope systems have several basic configurations. Some use a focusing lens to concentrate X-rays onto the object under study and / or an objective lens to image the object with X-rays after interaction. The resolution and aberrations associated with these types of microscopes are usually determined by the spectral characteristics of the X-rays. Some microscope systems employ a projection configuration in which a small X-ray source spot is often used, along with geometric magnification, to image the object.

[0005] Performance, and especially resolution, is affected by different factors. Since projection configurations are aberration-free, resolution is typically determined by the size of the X-ray source spot. Ideally, the X-ray source spot is a point spot. In reality, X-ray source spots are considerably larger. Generally, the source spot size is determined by the electron optics and their ability to focus the electron beam to a single point. Source spot sizes are generally around 50–200 micrometers (μm) with good electron optics, but in other examples, where output is a more critical performance index, the X-ray source spot size may be 1–5 millimeters (mm). For transmission target X-ray sources, spot sizes of a few micrometers, such as 1–5 μm, are common. In fact, some transmission sources have spot sizes up to 150 nanometers (nm). In any case, the size of the X-ray source generally limits the resolution of an X-ray projection microscope.

[0006] In many microscopy applications, transmission target X-ray sources are frequently used. In the basic configuration of an X-ray tube, thermionic or field-emission electrons are generated at the cathode (filament) of the vacuum tube and accelerated to the anode (forming an electron beam shaped by different electrostatic and magneto-optical elements). For example, magnetic lenses often use a coil of copper wire inside an iron pole piece. The current passing through the coil generates a magnetic field within the bore of the pole piece. Electrostatic lenses generate an electrostatic field using a charged dielectric. The electron beam then strikes the back surface of a typically thin target, common target materials being, for example, tungsten, copper, and chromium. The X-rays emitted from the front surface of the target are then used to irradiate an object. [Overview of the project] [Means for solving the problem]

[0007] Summary of the Invention In this configuration, a "smart" gun controller controls the electron emitter and the formation of the electron beam. To improve thermal management, an oil container houses the emitter's high-voltage generator and the gun controller. In addition, initial piloting is performed when the beam is being accelerated. This initial piloting is performed by a source coil, which often consumes very little power. This piloting ensures that the electron beam passes through the aperture, which is part of the anode.

[0008] However, at very high vacuums, removing heat from the source coil can become a problem. The coil can overheat significantly, causing coil damage, and the vacuum quality can also degrade due to gas release from the heated components (the coil itself, the coil carriers, and any other components that absorb heat from the coil and are exposed to the vacuum). Furthermore, the thermal load is very likely to alter the electron optics as mechanical components move due to thermal expansion. Therefore, it is desirable to generate the magnetic field in a vacuum close to the electron emitter without the problems associated with heat generated from the coil.

[0009] The solution involves generating a magnetic field outside the vacuum vessel, allowing for cooling with air / water / oil to remove all unwanted heat from the source coil. The magnetic field is then picked up within the vacuum vessel, which contains magnetic pole pieces, and directed towards areas where a magnetic field is needed, such as in front of the anode or near the electron emitter, to steer and control the electron beam. Two magnetic pole pieces form a magnetic pole pair.

[0010] Typically, for each desired pole pair near a charged moving particle beam (such as an e-beam), a vacuum transition exists between one source coil and one pole piece.

[0011] Magnetically penetrating vacuum transitions can be performed in any non-magnetic material (such as ceramic or aluminum) or weakly magnetizable material (such as stainless steel).

[0012] In general, according to one embodiment, the present invention features an X-ray source. This source comprises a vacuum vessel, a target within the vacuum vessel, and an electron source within the vacuum vessel for generating electrons to form a beam for impacting the target to produce X-rays. Finally, there is a source coil located outside the vacuum vessel for magnetically steering the beam near the electron emitter on its path toward the target.

[0013] In the embodiment, the X-ray source further comprises a high-voltage generator for supplying power to an electron emitter and an oil container disposed within a vacuum vessel housing the high-voltage generator. Preferably, the source coil is located within the oil container.

[0014] In addition, the source coil steers and controls the electron beam in the region between the electron emitter (filament) and the anode as the electrons are accelerated.

[0015] A magnetically penetrating vacuum transition wall plug can be added to the oil container to better transmit the magnetic field from the source coil to the pole piece.

[0016] In the embodiment, pole pieces are used to guide the magnetic field from the source coil to the beam through a vacuum. These pole pieces may be supported by a protective region cap that at least partially covers the electron source.

[0017] In the current configuration, a flight tube assembly is provided, with the target attached to the end of the flight tube assembly. A magnetic focusing lens and / or flight tube steering coil are positioned around the flight tube assembly to guide the beam from the flight tube aperture toward the target and downward from the flight tube assembly. In some embodiments, the flight tube aperture may be a beam definition aperture.

[0018] In general, according to another embodiment, the present invention features an X-ray source comprising a vacuum vessel, a target within the vacuum vessel, an electron source within the vacuum vessel for generating electrons to form a beam that collides with the target to produce X-rays, a high-voltage generator for supplying power to the electron source, and an oil vessel within the vacuum vessel. A gun controller controls the electron emitter and the formation of the electron beam. To improve thermal management, the oil vessel houses both the high-voltage generator and the gun controller.

[0019] The use of transformer oil media from high-voltage generators, as well as the use of cooling source coils and / or gun controllers, also offers advantages.

[0020] Preferably, a heat exchanger is placed inside the oil container. Currently, water flows through the heat exchanger to remove heat, but other liquid coolants can certainly be used. Some embodiments may include an oil immersion pump to allow the flow of oil within the oil container.

[0021] In a preferred embodiment, the circulator is used to cool the heat exchanger and other components.

[0022] The above and other features of the present invention, including various novel details of the structure and component combinations, as well as other advantages, will be described in more detail with reference to the accompanying drawings and pointed out in the claims. It will be understood that the specific methods and apparatuses embodying the present invention are shown by way of illustration and not as limitations of the present invention. The principles and features of the present invention can be used in various and numerous embodiments without departing from the scope of the present invention.

[0023] In the accompanying drawings, reference numerals refer to the same parts throughout different figures. The drawings are not necessarily to scale and instead emphasis is placed on explaining the principles of the present invention.

Brief Description of the Drawings

[0024] [Figure 1] It is a schematic cross-sectional view of an X-ray source according to the present invention.

Modes for Carrying Out the Invention

[0025] Modes for Carrying Out the Invention Next, the present invention will be described more fully hereinafter with reference to the accompanying drawings which show exemplary embodiments of the present invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the present invention to those skilled in the art.

[0026] Where used herein, the term “and / or” includes any combination of one or more of the related enumerated items. Furthermore, all conjunctions used should be understood in the most comprehensive sense possible. Thus, the word “or” should be understood to have a logical “or” definition rather than a logical “exclusive or” definition, unless the context clearly requires otherwise. Additionally, the singular forms and the articles “a,” “an,” and “the” are intended to include the plural forms unless otherwise specified. Where used herein, the terms “includes,” “comprises,” “and / or,” and “including” identify the presence of the described features, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof. Furthermore, where an element containing a component or subsystem is mentioned and / or indicated as being connected or coupled to another element, it should be understood that it may be directly connected or coupled to the other element, or an intervening element may exist.

[0027] In this specification, terms such as "first" and "second" are used to describe various elements, but it will be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. Thus, the elements described below may be called second elements, and similarly, second elements may be called first elements without departing from the teachings of the present invention.

[0028] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having the same meaning as their meanings in the context of the relevant art, and it will be further understood that they should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0029] Figure 1 is a schematic cross-sectional view of an X-ray source 100 configured according to the principle of the present invention. The illustrated embodiment is a “transmission target” source. Electron beam B strikes the target in the target assembly 500, and the X-rays emitted from the opposite side of the target are used to illuminate the object. However, many aspects of the following innovations are equally applicable to other X-ray tube source configurations, including side windows, rotating anodes, and metal jet anodes.

[0030] Generally, an X-ray source comprises a vacuum chamber 112 and an oil container 114 placed inside the vacuum chamber. Preferably, the vacuum chamber 112 is made of a metal such as aluminum or stainless steel for its strength against vacuum. The oil container 114 is preferably made of a non-conductive material such as ceramic, for example sintered alumina, which provides electrical insulation to prevent arc discharge to the high-voltage components it contains.

[0031] The vacuum generator 118 is used to draw and / or maintain a vacuum over the vacuum chamber 112. In one example, an ion pump is used.

[0032] A heat exchanger 119 is located inside the oil container. For this purpose, a plate heat exchanger can be used to remove thermal energy (heat) from the oil and transfer it to a coolant such as water that circulates through the exchanger. Some embodiments further employ an oil immersion pump 121 to circulate the oil within the oil container 114. In a preferred embodiment, a circulator 152 is used to move the coolant into the heat exchanger 119 and carry away the heat from the oil.

[0033] Generally, the vacuum vessel 112 defines a volumetric vacuum region through which the electron beam B propagates from an electron emitter 126 (filament or cathode), typically located near the distal end of the oil vessel 114, to a target held by the target assembly 500. The vacuum region also preferably surrounds at least a portion of the oil vessel, which houses high-voltage components and provides high-voltage insulation.

[0034] The system controller 200 is located outside both containers 112 and 114. It includes a main controller and a data interface to external devices. It also includes a power supply for connection to the mains power supply. In addition, it controls the vacuum generator 118 and the circulator 152.

[0035] The high-voltage generator 116 is located within the oil container 114. Its base is located proximal to the oil container 114, allowing it to receive power from the system controller 200. The high-voltage generator 116 is immersed in the oil contained in the oil container 114 for thermal control and high-voltage insulation. The oil is primarily required to keep the generator 116 relatively small. However, it can also be used to pot the generator 116. Moving distally, the high-voltage generator 116 is further electrically insulated from the environment by the oil in the vacuum container 112 and the surrounding vacuum.

[0036] In the current example, the high-voltage generator 116 generates an acceleration voltage of negative 20–160kV, which powers the gun controller 300, in particular, which controls the electron source (emitter or filament). The high-voltage generator biases the entire gun controller to this large negative voltage so that the generated electrons accelerate toward a smaller negative voltage and towards ground.

[0037] The inner container 120 is located distal to the distal end of the high-voltage generator 116. The inner container 120 is immersed in the oil of the oil container 114. In the present embodiment, the inner container is preferably made of a metal such as aluminum and soft iron. It is also filled with oil, which helps in the transfer of heat from the electronic equipment as well as from the source coil, and this will be discussed later.

[0038] The gun controller 300 is housed within the inner container 120, which also functions as a Faraday cage for electrically protecting the controller 300. It drives the electron emitter and provides control for the electron emitter, beam generation, adjustment, and steering.

[0039] The electron emitter, for example, filament 126, is held within a filament mount 124. In the present example, the electron emitter 126 includes a lanthanum hexaboride (LaB6) crystal and a carbon heater rod. This protrudes into the vacuum of the vacuum vessel to function as a thermionic electron source or electron emitter (cathode). Other configurations such as W, CeB6, HfC, and carbon nanotube filaments are also possible.

[0040] The vacuum feedthrough 122 provides an electrical connection between the gun controller 300 in the inner container 120 and the outer wall of the oil container 114 via the oil contained in the oil container 114.

[0041] The suppressor electrode or Wehnelt cap 127 is attached to the distal side of the filament mount 124 and covers the filament 126. Electrons emitted from the filament 126 pass through the central aperture of the suppressor electrode 127. Its voltage is controlled by the gun controller 300.

[0042] The protective area cap 138 has a general bell shape, extends over the electron emitter 126 and its filament mount 124, and rewinds to the distal end of the oil container 114. Its distal end supports the first or extractor anode 140. The voltage and cap of the first anode are controlled by the gun controller 300 to accelerate the emitted electrons into beam B and pass through the central aperture 141 of the first anode 140. Thus, during operation, the electron beam passes through the central aperture 141 of the first anode 140.

[0043] However, the first anode is not necessary. The system can also be designed without this first anode and rely on other means to accelerate electrons.

[0044] Beam B is guided through the aperture of the flight tube aperture assembly 142 in the distal wall of the vacuum vessel 112. This flight tube aperture assembly acts as a second anode and is currently held at ground potential 143. Thus, by biasing the gun controller to a large negative voltage, electrons are further accelerated in the gap between the first anode 140 and the flight tube assembly 142.

[0045] In other embodiments, the flight tube aperture assembly 142 is electrically isolated from the vacuum vessel 112 using an insulating gasket such as diamond. A voltage generator is also added to supply a controlled potential to the flight tube aperture assembly. In this configuration, the system controller 200 also controls the voltage of this second anode to provide further control, such as further acceleration of the electron beam B.

[0046] The flight tube assembly 400 extends a vacuum to the target assembly 500, and then to the target. The flight tube manifold 150 provides liquid cooling to the target assembly through the walls of the flight tube assembly using a coolant such as water from the circulator 152.

[0047] Along the flight tube assembly 400, a flight tube beam maneuvering and shaping system 600 is positioned to adjust the electron beam and guide the beam to any position on the target. This is done by the flight tube assembly 400 and the beam maneuvering and shaping system 600, which guides the electron beam B through a magnetic focusing lens 700 to a desired angle and position. Since the target is consumed during operation, beam maneuvering generally positions the spot at different locations on the target.

[0048] Furthermore, a magnetic focusing lens 700 is positioned along the flight tube assembly 400 to focus beam B onto the target.

[0049] Preferably, both the flight tube beam maneuvering and shaping system 600 and the magnetic focusing lens 700 are cooled by a coolant circulated from the circulator 152 and controlled by the system controller 200.

[0050] A set of source coils 132N, 132S (front and back in the image plane), not shown, and 132E, 132W and their respective cores 134N, 134S, 134E and 134W are integrated with an oil container 114, a gun controller inner container 120, and a protective area cap 138. The coils are located outside the vacuum of the vacuum container. In one example, they may be located on the outer wall of the vacuum container exposed to the ambient atmosphere. In the illustrated example, the source coils 132N, 132S, 132E, and 132W are located in the oil container and thus efficiently cooled by the contained oil, but the coils could also be potted instead.

[0051] More generally, oil can be replaced with potting material or other high-voltage cooling materials such as Fr-77 by Sigma Aldrich, Sf6-Novec 4710 by 3M, or C3F7CN.

[0052] More specifically, the two source coils 132N and 132S are generally positioned above and below the filament 126. Two additional source coils 132E and 132W are positioned on the other two axes below and above the plane of the drawing, respectively. The North Pole section 130N and the South Pole section 130S extend from the cores 134N and 134S of the source coils 132N and 132S, respectively, wrap around inside the protective area cap 138, and converge above and below the central aperture 141 of the first anode 140, respectively. Similarly, the east pole piece 130E and the west pole piece 130W (in the other two axes, lower and upper, respectively, in the plane of the drawing) extend from the cores 134E and 134W of the source coils 132E and 132W, wrap around the inner sides of the protective area cap 138, and converge to the left and right of the central port 141, respectively, thereby forming a magnetic circuit surrounding the emitter in vacuum.

[0053] The pole pieces 130N, 130S, 130E, and 130W can be mechanically connected to virtually anything within the emitter region. Therefore, although they are supported by the protective region cap in the illustrated embodiment, they do not need to be directly connected. That said, in the present example, the pole pieces 130N, 130S, 130E, and 130W are connected to the protective cap, which is electrically at the potential of the first anode 140.

[0054] An annular ring-shaped yoke 135 is positioned proximal to the cores 134N, 134S, 134E, and 134W and is manufactured as part of the vessel 120 to improve the magnetic circuit. In fact, in the present embodiment, the distal end of the inner vessel 120 is made of soft iron and thus completes the magnetic circuit by inducing magnetic flux between the cores.

[0055] In a preferred embodiment, the magnetic circuits for the source coils 132N, 132S, 132E, and 132W are further improved by magnetizable or ferromagnetic wall plugs 136N, 136S, 136E, and 136W. These wall plugs are inserted into holes formed in an oil container 114 opposite the distal ends of the respective cores 134N, 134S, 134E, and 134W. This improves the magnetic flux through the circuit. Specifically, the plugs minimize the gap between the coil cores 134N, 134S, 134E, and 134W and the respective pole pieces 130N, 130S, 130E, and 130W.

[0056] In some cases, plugs 136N, 136S, 136E, and 136W are inserted into pre-drilled holes in the ceramic oil container 114. Alternatively, the same can be done by welding nickel-cobalt iron alloy or soft iron plugs into pre-drilled holes in the stainless steel vacuum chamber 112. Other combinations are also possible.

[0057] In the current embodiment, source coils 132N, 132S, 132E, and 132W are driven and operated in current-controlled mode by the gun controller 300. Feedback is obtained indirectly by measuring the amount of beam traveling through the “anode aperture” onto the target, provided by a system controller 200 which provides this information to the gun controller. The source coils are controlled by the gun controller 300, which steers the electron beam near its source, specifically within the gap between the filament 126 and the first anode 140, to steer the beam when it is first accelerated.

[0058] Although the present invention has been specifically shown and described with reference to its preferred embodiments, it will be understood by those skilled in the art that various modifications in form and detail can be made without departing from the scope of the invention as encompassed by the appended claims.

Claims

1. It is an X-ray source, Vacuum container and An electron emitter, which is placed inside the vacuum vessel, generates electrons to form an electron beam and collides it with a target to generate X-rays, A high-voltage generator for accelerating the aforementioned electrons, The electron emitter and the gun controller that controls the formation of the electron beam, The oil container in the vacuum vessel housing the high voltage generator and the gun controller, The vacuum vessel comprises a source coil located outside the vacuum to perform the initial maneuvers for generating the electron beam, An X-ray source, wherein the gun controller is configured to control the electron emitter and the source coil to control the formation of the electron beam.

2. The X-ray source according to claim 1, further comprising an inner container within the oil container for housing the gun controller.

3. The X-ray source according to claim 2, wherein the inner container is filled with oil.

4. The X-ray source according to claim 1, wherein the electron emitter is a filament.

5. The X-ray source according to claim 1, further comprising a suppressor electrode on the electron emitter.

6. The X-ray source according to claim 5, further comprising a protective area cap on the suppressor electrode.

7. The X-ray source according to claim 1, further comprising an anode for accelerating the electrons from the electron emitter.

8. The X-ray source according to claim 7, further comprising a protective area cap electrically connected to the anode.

9. The X-ray source according to claim 1, further comprising a flight tube, wherein the target is located at the end of the flight tube.

10. It is an X-ray source, Vacuum container and An electron emitter placed inside the vacuum vessel to generate electrons, An anode for accelerating the aforementioned electrons to form an electron beam and colliding it with a target to generate X-rays, The system comprises a source coil located outside the vacuum of the vacuum chamber for magnetically maneuvering the electron beam during the acceleration of the electrons, A high-voltage generator that generates a voltage for accelerating the aforementioned electrons, The vacuum container housing the high-voltage generator further comprises an oil container, The aforementioned source coil is an X-ray source located inside the oil container.

11. The X-ray source according to claim 10, further comprising a wall plug in the oil container for transmitting a magnetic field from the source coil to the electron beam.

12. The X-ray source according to claim 10, further comprising a heat exchanger for removing heat from the oil in the oil container.

13. The X-ray source according to claim 10, further comprising an oil immersion pump for circulating oil within the oil container.

14. The X-ray source according to claim 10, further comprising a magnetic pole piece for guiding a magnetic field from the source coil to the electron beam through the vacuum.

15. The X-ray source according to claim 14, wherein the pole piece is supported on the electron emitter by a protective region cap.

16. The X-ray source according to claim 10, further comprising a flight tube assembly, wherein the target is attached to the end of the flight tube assembly, and the source coil guides the electron beam into the flight tube assembly.

17. The X-ray source according to claim 14, further comprising a flight tube aperture, wherein the source coil guides the electron beam through the flight tube aperture.

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