Fluid-cooled reflective x-ray source

Abstract

To provide a water-cooled reflective x-ray source providing water or other fluid cooling of the centering aperture, x-ray target, and / or exit window so as to solve the problem in which: during operation of a reflection target x-ray source, heat must be removed from many components; an electron beam must be steered to the target and may interact with structures along this path; there is also heat generated in the target itself; this can be excessive since only a very small percentage of the electron beam's energy is transformed into x-rays; and finally the x-rays must exit the vacuum through a window, which can also be heated both by the x-rays, reflected electrons, and radiant heat from the target.SOLUTION: An x-ray source comprises: a target; an electron beam source for generating an electron beam for striking the target to generate x-rays; and a fluid-cooled aperture tube including a centering aperture between the electron beam source and the target.SELECTED DRAWING: Figure 2

Description

Background Art

[0001] Background of the Invention 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 an electron beam is generated and collided with a target are often used. The obtained X-rays include characteristic lines determined by the elemental composition of the target and extensive bremsstrahlung.

[0002] There are several basic configurations in X-ray microscope systems. Some use condenser lenses to focus X-rays on the object of study and / or objective lenses to image the X-rays after interaction with the object. 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 where a small X-ray source spot is often used with geometric magnification to image the object.

[0003] Performance and especially resolution are affected by different factors. Since there are no aberrations in the projection configuration, the resolution is usually determined by the size of the X-ray source spot. Ideally, the X-ray source spot is a point spot. In reality, the X-ray source spot is quite large. Generally, the X-ray source spot size is determined by the electron optics and the ability of those optical systems to focus the electron beam to a point. The X-ray source spot size is generally about 5 to 200 micrometers (μm) using good electron optics systems. However, in other examples, when output is a more important performance index, the X-ray source spot size can be 1 to 5 millimeters (mm). In the case of a transmission type target X-ray source, a spot size of several micrometers such as 1 μm to 5 μm is common. In any case, the size of the X-ray source generally limits the resolution of the X-ray projection microscope.

[0004] Many microscopy applications utilize reflective target X-ray sources. In the basic configuration of an X-ray tube, thermionic or field-emission electrons are generated at the cathode (filament) inside the vacuum tube and accelerated to the anode in a vacuum (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 flowing through the coil generates a magnetic field within the bore of the pole piece. The electron beam then strikes the target at an oblique angle. The X-rays then typically pass through a window that is highly penetrating to X-rays but can maintain a vacuum. Common target materials include, for example, tungsten, copper, and chromium. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Summary of the Invention During the operation of a reflection target X-ray source, heat must be removed from many components. The electron beam must be directed towards the target and may interact with the structure along this path. Heat is also generated in the target itself. This can be excessive, as only a small percentage of the electron beam's energy is converted into X-rays. Finally, the X-rays must escape the vacuum through a window, and this window may also be heated by the X-rays, reflected electrons, and radiant heat from the target. [Means for solving the problem]

[0006] In general, according to one embodiment, the present invention is characterized by an X-ray source comprising a target, an electron beam source for generating an electron beam to collide with the target and generate X-rays, and a fluid-cooled centering aperture between the electron beam source and the target.

[0007] In this embodiment, the opening tube has an inner diameter that decreases in the direction of the target, and the opening tube can extend between the focus yoke and the head body.

[0008] A sheath tube surrounding the open tube may be useful, and the fluid circulates between the sheath tube and the open tube. Finally, it is preferable to place a baffle between the sheath tube and the open tube to guide the fluid flow.

[0009] Generally, in another embodiment, the present invention features a method of operating an X-ray source that includes using a flight tube beam maneuvering system to steer an electron beam through an aperture tube to generate X-rays during an X-ray generation mode, and deactivating the X-rays by controlling the flight tube beam maneuvering system to steer the beam away from the opening of the aperture tube.

[0010] In this embodiment, the open tube can be fluid-cooled. Alternatively, a sheath tube can be used to surround the open tube, and a baffle can be placed between the sheath tube and the open tube to guide the fluid.

[0011] In the embodiment, the window includes diamond. In addition, it may include a head body having an X-ray port formed in the head on the distal side of the window.

[0012] Channels can be formed in the head body, and the channels can extend around the window. Furthermore, input and output channels may be formed in the head body to allow fluid to flow through the channels.

[0013] In general, according to another embodiment, the present invention is characterized by an X-ray source comprising a target, an electron beam source for generating an electron beam to collide with the target, and a diamond window from which X-rays are emitted.

[0014] In general, according to another embodiment, the present invention is characterized by an X-ray source comprising a target, an electron beam source for generating an electron beam to collide with the target, and a scattered electron detector for detecting electrons scattered from the target.

[0015] In general, according to another embodiment, the present invention features an X-ray source comprising an electrically insulated target, an electron beam source for generating an electron beam to collide with the target and generate X-rays, a fluid cooling opening tube with a centering opening between the electron beam source and the target, a diamond fluid cooling window from which the X-rays are emitted, a scattered electron detector for detecting electrons scattered from the target, and a fluid cooling loop for flowing fluid across the back surface of the target.

[0016] In general, according to another embodiment, the present invention features an X-ray source comprising an electrically insulated target, an electron beam source for generating an electron beam to collide with the target and generate X-rays, and a fluid cooling loop for flowing a fluid across the back surface of the target.

[0017] In general, according to another embodiment, the present invention is characterized by an X-ray source comprising a target, an electron beam source for generating an electron beam to collide with the target, and a fluid cooling window from which X-rays are emitted.

[0018] The above and other features of the present invention, including various novel details of the structure and combination of components, 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 specific methods and apparatus embodying the present invention are shown as examples, not as limitations of the invention. The principles and features of the present invention can be used in various and numerous embodiments without departing from the scope of the invention.

[0019] Brief explanation of the drawing In the attached drawings, reference numerals indicate the same parts across different drawings. The drawings are not necessarily to scale. Instead, the focus is on illustrating the principles of the present invention. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic cross-sectional view of a reflective X-ray source. [Figure 2]Cross-sectional view of a focus lens head assembly 300 according to the present invention. [Figure 3] Cross-sectional view showing a water-cooled centering aperture assembly 400 according to the present invention. [Figure 4] Cross-sectional view of a water-cooled target cartridge attached to a head body according to the present invention. [Figure 5] Perspective view showing a head body and water cooling of an X-ray port window according to the present invention.

Mode for Carrying Out the Invention

[0021] Detailed Description of Preferred Embodiments Next, the present invention will be more fully described below with reference to the accompanying drawings showing 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 described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art.

[0022] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Further, the singular forms as well as the articles "a", "an", and "the" are intended to include the plural forms as well, unless specifically stated otherwise. As used herein, the terms "include", "comprise", "including", and / or "comprising" specify the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Further, it will be understood that when an element including a component or subsystem is referred to and / or shown as being connected or coupled to another element, it may be directly connected or coupled to the other element or intervening elements may be present.

[0023] Unless otherwise defined, all terms (including technical and scientific terms) used herein shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries shall be interpreted as having a meaning that coincides with their meaning in the context of the relevant art, and it should be further understood that they are not to be interpreted in an idealized or overly formal sense unless explicitly defined as such herein.

[0024] FIG. 1 is a schematic cross-sectional view of an X-ray source 100. The illustrated embodiment is a “reflection target type” X-ray source. The electron beam B impinges on the target within the focus lens head assembly 300 at an oblique angle, and the X-rays emitted from the target are used to irradiate an object. That being said, many aspects of the following technological innovations are equally applicable to other X-ray tube source configurations including rotating anodes and metal jet anodes.

[0025] Generally, the X-ray source includes a vacuum vessel 112. Preferably, the vacuum vessel 112 is a metal such as aluminum or stainless steel for strength against vacuum. Generally, the vacuum vessel 112 defines a volumetric measurement vacuum region in which the electron beam B propagates from the electron emitter 126 (filament or cathode) to the target within the focus lens head assembly 300.

[0026] The system controller 200 is disposed outside the vacuum vessel 112. This includes a main controller and a data interface to external devices. It also includes a power supply for connection to the main power source.

[0027] The high voltage generator 116 generates power at the voltage required by the electron emitter 126. The high voltage generator 116 in this example generates a negative acceleration voltage of several tens to several hundreds of kilovolts. The high voltage is provided via the power supply umbilical 170.

[0028] The container body 172 protrudes from the proximal side of the container into the volumetric measurement area defined by the vacuum vessel 112. It has an internal umbilical port 174 extending distally through the container body 172, allowing the power umbilical to reach the umbilical plug assembly 176.

[0029] The electron emitter, for example, the filament 126, is held within a filament mount 124 supported at the distal end of the vessel body 172. In this example, the electron emitter 126 includes a tungsten hairpin, which protrudes into the vacuum of the vacuum vessel to function as a thermionic electron source or electron emitter (cathode). Other configurations are also possible, such as lanthanum hexaboride (LaB6) crystals and carbon heater rods, CeB6, HfC, and carbon nanotube filaments.

[0030] The protective field cap 138 extends over the electron emitter 126 and its filament mount 124 and has a general bell shape that curves back to the distal end of the vessel body 172. Its distal end functions as a suppressor or grid anode 140, which helps to adjust the shape and intensity of the emitted electrons forming beam B.

[0031] Beam B is guided into a flight tube 150 attached to the distal wall of the vacuum vessel 112.

[0032] Along the flight tube 150, a flight tube beam steering and shaping system is positioned to adjust the electron beam and guide it to the center of the next focus lens and head assembly 300. Preferably, the flight tube beam steering and shaping system includes a first octupole steering system 160 and a second octupole steering system 162. Each of these octupole systems comprises eight electromagnet coils that generate a magnetic field under the control of a system controller 200 to guide and shape the electron beam B.

[0033] Next, the electron beam is received by a focusing lens and head assembly 300, which has a reflection target upon which the electron beam collides to generate an X-ray beam X.

[0034] Figure 2 is a cross-sectional view of the reflective target assembly 300. The flight tube 150 extends into the focus yoke 310. The flight tube 150 is coaxial with the yoke beam port 320, which is formed through the yoke central body 312. To provide a vacuum seal, a flight tube / yoke O-ring 340 is positioned between the outer circumference of the flight tube and the inner wall of the yoke beam port 320.

[0035] The yoke central body 312 is surrounded by the focus coil 330. Current is supplied to the focus coil 330 from the system controller 200 by a pair of coil lead wires 332. These lead wires pass through yoke wire ports 326 formed in the annular yoke rear body 318. The yoke rear body 318 extends outward from the proximal part of the yoke central body 312 to the yoke outer periphery 314. This yoke outer periphery is a hollow cylindrical shape that extends along the outer circumference of the focus coil 330 and includes ports 316 for circulating cooling water.

[0036] The yoke cap 322 has a nearly hollow frustoconical shape. Its proximal end engages with the distal end of the yoke outer periphery 314. As it moves distally, it converges to the central axis and terminates at the distal magnetic pole tip 342. Meanwhile, the yoke central body protrudes distally and terminates at the proximal magnetic pole tip 324.

[0037] The centering opening assembly 400 is coaxial with the flight tube 150 and the yoke beam port 320. It extends between the distal end of the yoke central body 312, specifically the pole tip 324, and the inner opening passing through the center of the yoke cap 322.

[0038] The centering opening 416 extends through the center of the yoke cap 322 and seals against the head body 502 of the tube head 500. This allows a vacuum to extend into the tube head so that the electron beam is coupled to the head beam port 510.

[0039] The target cartridge 600 holds the target 610 in the head beam port 510. As a result, the electron beam passing through the head beam port 510 can collide with this target 610 at an oblique angle. The generated X-rays enter the head X-ray port 512 and then exit the volume through the X-ray port window 520.

[0040] Figure 3 is a cross-sectional view showing the water-cooled centering opening assembly 400. Generally, the centering aperture can be subjected to thermal stress. Electron beam B can contain high levels of power, and the centering aperture can absorb some or all of that power depending on the operating mode of the source. Furthermore, the heat generated at the centering aperture can affect other components, such as the focus lens system 300. Thermal cycling can affect its operation. High temperatures can damage the vacuum-sealed O-rings and the focus coil 330.

[0041] This embodiment provides water cooling for a centering opening assembly 400. In fact, the centering opening is directly water-cooled.

[0042] More specifically, the sheath tube 410 extends into the distal end of the yoke beam port 320 of the yoke central body 312. To maintain a vacuum in the flight tube system, a yoke / sheath O-ring 418 is used between the inner wall of the enlarged end of the yoke beam port 320 and the outer surface of the sheath tube 410. In fact, the yoke / sheath O-ring 418 is held within an annular notch 410C formed on the outer surface of the sheath tube 410. Its inner surface defines the sheath tube beam port 410P. The open tube 412 is concentrically positioned inside the sheath tube 410. The proximal end 422 of the open tube 412 is preferably brazed to the inner wall of the sheath tube and communicates with the yoke beam port 320. The distal end of the open tube 412 communicates with, and specifically seals with, the head beam port 510 formed in the head body 502. The baffle 414 is arranged concentrically between the sheath tube and the open tube 412, and its distal end seals against the head body 502.

[0043] The proximal end 422 of the open tube 412 has a frustoconical shape for sealing against the inner wall of the sheath tube 410. This proximal end narrows as it moves distally, forming a centering opening 416. Thus, the open tube 412 has an inner diameter that decreases in the direction of the target.

[0044] The baffle 414 forms a flow path between the outer wall of the open pipe 412 and the inner wall of the sheath pipe 410. Specifically, the head body 502 has a head opening water inlet port 516 which connects to a channel between the inner wall of the sheath pipe 410 and the outer wall of the distal end of the baffle 414. Similarly, a head opening water outlet port 518 is formed in the head body 502 which communicates with the region between the outer wall of the open pipe 412 and the inner wall of the distal end of the baffle 414. In this way, water is pumped to circulate along the length of the sheath pipe 410 and the open pipe 412 to remove the generated heat.

[0045] The centering aperture can also be reduced in diameter and thus converted into a beam aperture, which can then be used to remove the outer portion of electron beam B, thus enabling the creation of a smaller focus on the target.

[0046] Generally, heat removal is important to protect the O-ring. The centering aperture can also be used as a beam dump when it is desired to quickly turn off the X-rays. This is often done while adjusting the beam power and focus to keep the target safe from burnout and to carefully control the X-ray dose applied to the sample. Specifically, the controller 200 controls the first octapole steering system 160 and the second octapole steering system 162 of the flight tube beam steering shaping system to steer the electron beam concentrically through the aperture tube 412 when generating X-rays. Then, to deactivate the X-rays, the controller controls the first octapole steering system 160 and the second octapole steering system 162 to steer the beam away from the centering aperture, resulting in the beam instead colliding with and grounding the proximal end 422 of the aperture tube 412, which is preferably directly water-cooled.

[0047] Figure 4 is a cross-sectional view of the water-cooled target cartridge 600. During operation, the electron beam collides with the target 610 and generates X-rays through interaction with the target metal layer 612. These X-rays are emitted through the head X-ray port 512 and the X-ray port window 520, thereby releasing the vacuum from the X-ray source.

[0048] In principle, the target 610 should also be cooled. Because the X-ray generation process is quite inefficient, a large portion of the energy of electron beam B is stored in the target 610 as heat. In the worst case, the electron beam could actually create a hole through the target. This is addressed in this embodiment by direct cooling of the target.

[0049] More specifically, the target 610 is attached to the end of the tubular end of the cartridge frame 620. The target metal layer 612 faces the head beam port 510. The metal layer 612 is formed on a target substrate 614 which is preferably brazed to the end of the cartridge frame 620. Preferably, the target substrate 614 is diamond to maximize thermal conductivity and minimize the risk of melting. Diamond can also be exposed to a large electron beam without compromising the vacuum seal. Therefore, even if the tungsten melts, the seal between the vacuum and the cooling water will not be compromised.

[0050] In this embodiment, the target metal layer 612 is electrically connected to the cartridge frame. The controller 200 monitors the target current and controls the target voltage via the target current / voltage control line 212.

[0051] The cartridge frame 620 is inserted into the head cartridge port 514 formed in the head body 502. The cartridge / head O-ring 628 is positioned between the shoulder of the cartridge frame 620 and the head body 502. This seals the vacuum of the head beam port 510.

[0052] The cartridge frame 620 is attached to and held in place by the arrangement of mechanical bolts 622. These bolts are inserted into bolt holes 626 in the cartridge frame 620 and screwed into threaded holes formed in the head body 502. This causes the shoulder portion of the cartridge frame 620 to be drawn into the head beam port 510 relative to the head body and target. This compresses the cartridge / head O-ring 628 to seal the vacuum.

[0053] In a preferred embodiment, the target metal layer 612 is electrically connected to the cartridge frame during the brazing process, and the cartridge frame 620 is electrically isolated from the head body 502. This allows for the detection of the current generated by the electron beam impacting the target 610, and the control of the target voltage by a controller via the target current / voltage control line 212.

[0054] This electrical isolation is provided in several ways. A cartridge insulating ring 620 ensures isolation between the shoulder portion of the cartridge frame 620 and the head body 502. Furthermore, the mechanical bolts 622 are electrically isolated from the cartridge frame 620 by a plastic insulating sleeve 624.

[0055] The port insert 650 is inserted into the cartridge frame 620. Insert water inlet port 652 and insert water outlet port 654 are formed through the port insert 650. This provides a water circulation channel that extends along the length of the cartridge frame 620, allowing water to circulate and come into contact with the back surface of the target 610. Water is supplied to these ports via the respective target supply pipe 660 and target return pipe 662.

[0056] Two O-rings, insert / cartridge front O-ring 656 and insert / cartridge rear O-ring 658, are positioned between the outer circumference of the port insert 650 and the inner wall of the cartridge frame 620. These provide a liquid-tight seal to ensure that water does not leak from the cooling loop of the target 610.

[0057] The port insert 650 is secured to the cartridge frame 620 by an insert thrust ring 664. Specifically, the thrust ring engages with the distal end of the port insert 650 and screws into a thrust ring thread 632 formed on the distal end of the cartridge frame 620. This thrust ring 664 is tightened into the cartridge frame 620, seating the port insert 650 inside the cartridge frame 620. It should also be noted that this configuration allows for loosening of the thrust ring and rotation of the target, causing the beam to strike a new area of ​​the target, but the target will eventually experience burnout. On the other hand, when fully tightened, the thrust ring mechanically stabilizes the target within the head.

[0058] Furthermore, it should be noted that in alternative embodiments, water is replaced with oil as the cooling fluid. Oil provides better electrical insulation and allows for better control of target voltage and target current monitoring. In addition, voltage control is also used to check whether there is adequate insulation between the target and ground. It is used to measure the leakage resistance of the target to the insulation by applying a voltage and then reading the leakage current.

[0059] In one embodiment, a scattered electron detector 672 is further provided in the head beam port 510 or optionally in the head X-ray port 512. This allows the controller 200 to monitor the magnitude of electrons scattered from the target 610 via the scattered electron monitor line 210. This signal is used by the system controller 200 to determine the amount of target burnout caused by the electron beam.

[0060] Figure 5 is a perspective view showing the head body and water cooling system of the X-ray port window 520. Generally, the X-ray port window should also be cooled. The window is necessary to maintain the vacuum within the radiation source. However, the cover is heated in several ways. Electrons can be reflected from the target 610 and then accumulate their energy in the X-ray port window 520. Furthermore, the X-rays themselves can be absorbed within the window. On the other hand, the cover should be kept at the coldest possible temperature. Often, in microscope projection configurations, the X-ray port window should be placed as close to the sample as possible to maximize the geometric magnification. However, this proximity can damage some samples if the port window becomes excessively hot due to blackbody radiation alone.

[0061] In this environment, a port channel 522 is provided coaxially around the X-ray port window. In this environment, this port channel 522 is manufactured in the head body 502. Water is supplied to the port channel 522 by a port input channel 528 and removed from the channel by a port output channel 530. The water in the channel is sealed by a channel cover 524 (see Figure 4) that seals the port channel 522. In this way, during operation, the heat generated in the diamond X-ray port window 520 is efficiently removed by the head body 502, and then the water circulating in the port channel 522 removes that heat. This keeps the temperature of the X-ray port window 520 low. At the same time, the diamond material is protected from damage by scattered electrons.

[0062] 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. Target and an electron beam source for generating an electron beam for impacting the target to generate x-rays; a fluid-cooled aperture tube including a centering aperture between the electron beam source and the target.

2. The x-ray source of claim 1 , wherein the apertured tube has an inner diameter that decreases in a direction toward the target.

3. The x-ray source of claim 1 , wherein the aperture tube extends between a focus yoke and a head body.

4. The X-ray source according to any one of claims 1 to 3, further comprising a sheath tube surrounding the aperture tube.

5. 5. The x-ray source of claim 4, wherein a fluid is circulated between the sheath tube and the aperture tube.

6. The x-ray source of claim 4 further comprising a baffle between the sheath tube and the aperture tube to direct fluid flow.

7. using a flight tube beam steering system to steer an electron beam through an aperture tube to generate x-rays during an x-ray generation mode; and deactivating the x-rays by controlling the flight tube beam steering system to steer the beam away from an opening in the aperture tube.

8. The method of claim 7 further comprising the step of fluid cooling the open-ended tube.

9. The method of claim 7 , wherein the apertured tube has an inner diameter that decreases in a direction toward the target.

10. The method of any one of claims 7 to 9, further comprising a sheath tube surrounding the open tube.

11. The method of claim 10 , further comprising circulating the fluid between the sheath tube and the open tube.

12. The method of claim 11 further comprising using a baffle between the sheath tube and the open tube to direct the fluid.

13. Target and an electron beam source for generating an electron beam for impacting the target; and a fluid-cooled window through which the x-rays exit.

14. The x-ray source of claim 13 , wherein the window comprises diamond.

15. Further comprising a head body, The x-ray source of claim 13 , wherein the head body includes an x-ray port formed therein distal to the window.

16. The x-ray source of claim 15 further comprising a channel formed in the head body.

17. The x-ray source of claim 16 , wherein the channel extends around the window.

18. 17. The x-ray source of claim 16, further comprising input and output channels formed in the head body for flowing a fluid through the channels.

19. 14. The x-ray source of claim 13, wherein the fluid is water.

20. Target and an electron beam source for generating an electron beam for impacting the target; and a diamond window through which the X-rays exit.

21. Target and an electron beam source for generating an electron beam for impacting the target; and a scattered electron detector for detecting electrons scattered from the target.

22. an electrically isolated target; an electron beam source for generating an electron beam for impacting the target to generate x-rays; and a fluid cooling loop for flowing a fluid across a backside of the target.

23. an electrically isolated target; an electron beam source for generating an electron beam for impacting the target to generate x-rays; a fluid-cooled aperture tube including a centering aperture between the electron beam source and the target; a diamond fluid-cooled window from which the X-rays exit; a scattered electron detector for detecting electrons scattered from the target; and a fluid cooling loop for flowing a fluid across a backside of the target.

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