X-ray source and method for generating x-ray radiation

Abstract

The present inventive concept relates to an X-ray source comprising: a liquid target source configured to provide a liquid target moving along a flow axis; an electron source configured to provide an electron beam; and a liquid target shaper configured to shape the liquid target to comprise a non-circular cross section with respect to the flow axis, wherein the non-circular cross section has a first width along a first axis and a second width along a second axis, wherein the first width is shorter than the second width, and wherein the liquid target comprises an impact portion being intersected by the first axis; wherein the x-ray source is configured to direct the electron beam towards the impact portion such that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation.

Claims

1. An X-ray source comprising: a liquid target source configured to provide a liquid target moving along a flow axis; an electron source configured to provide an electron beam; and a liquid target shaper configured to shape the liquid target to comprise a non-circular cross section in a plane perpendicular to the flow axis, wherein the non-circular cross section has a first width along a first axis and a second width along a second axis, wherein the first width is shorter than the second width, and wherein the liquid target comprises an impact portion being intersected by the first axis; wherein the X-ray source is configured to direct the electron beam towards the impact portion such that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation; and wherein the X-ray source further comprises a first arrangement configured to move a location, within the impact portion, in which the electron beam interacts with the liquid target; the X-ray source further comprising a second arrangement configured to: scan the electron beam between the liquid target and an unobscured portion of a sensor area arranged to be at least partly obscured by the liquid target; determine a width of the liquid target based on a signal from the sensor area; and based on the determined width, adjust an angle of incidence between the electron beam and a surface of the impact portion.

2. The X-ray source according to claim 1, wherein the first arrangement is an electron optics arrangement configured to move the electron beam relative to the liquid target.

3. The X-ray source according to claim 1, wherein the first arrangement is configured to cooperate with the liquid target shaper to move the location, within the impact portion, in which the electron beam interacts with the liquid target.

4. The X-ray source according to claim 3, wherein the first arrangement is configured to rotate the target shaper around the flow axis.

5. The X-ray source according to claim 3, wherein the first arrangement is configured to move the target shaper in a direction orthogonal to the flow axis.

6. The X-ray source according to claim 3, wherein the first arrangement is configured to tilt the target shaper relative to the flow axis.

7. The X-ray source according to claim 1, wherein the liquid target shaper comprises a nozzle having a non-circular opening in order to shape the liquid target to comprise the non-circular cross section.

8. The X-ray source according to claim 7, wherein the arrangement is configured to move the nozzle along the flow axis in order to adjust a location and/or orientation of the impact portion in relation to the electron beam.

9. The X-ray source according to claim 7, wherein the non-circular opening has a shape selected from the group comprising elliptic, rectangular, square, hexagonal, oval, stadium, and rectangular with rounded corners.

10. The X-ray source according to claim 1, wherein the liquid target shaper comprises a magnetic field generator configured to generate a magnetic field for shaping the liquid target to comprise the non-circular cross section.

11. The X-ray source according to claim 10, wherein the magnetic field generator is configured to adjust the magnetic field in order to adjust a location and/or orientation of the impact portion in relation to the electron beam.

12. The X-ray source according to claim 1, wherein the electron source is configured to generate a plurality of electron beams interacting with the liquid target within the impact portion.

13. The X-ray source according to claim 1, wherein the liquid target is a metal.

14. A method for generating X-ray radiation, the method comprising: providing an electron beam; providing a liquid target moving along a flow axis, the liquid target comprising a non-circular cross section in a plane perpendicular to the flow axis, wherein the non-circular cross section has a first width along a first axis and a second width along a second axis, wherein the first width is shorter than the second width, and wherein the liquid target comprises an impact portion being intersected by the first axis; directing the electron beam towards the impact portion such that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation; and moving a location, within the impact portion, in which the electron beam interacts with the liquid target; the method further comprising: scanning the electron beam between the liquid target and an unobscured portion of a sensor area arranged to be at least partly obscured by the liquid target; determining a width of the liquid target based on a signal from the sensor area; and based on the determined width, adjusting an angle of incidence between the electron beam and a surface of the impact portion.

15. The method according to claim 14, further comprising: based on the determined width, performing at least one of: rotating the impact portion around the flow axis; and moving the location in which the electron beam interacts with the liquid target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description of different embodiments of the present inventive concept, with reference to the appended drawings, wherein:

(2) FIG. 1a schematically illustrates an X-ray source;

(3) FIG. 1b schematically illustrates an X-ray source provided with a magnetic field generator;

(4) FIG. 2 schematically illustrates a perspective view of a liquid target;

(5) FIG. 3 schematically illustrates a non-circular cross section of a liquid target;

(6) FIGS. 4a-4b schematically illustrate a movement of an electron source in order to adjust an angle of incidence and/or a location of an interaction region;

(7) FIG. 4c schematically illustrate a non-circular cross section of a liquid target being impinged by a plurality of electron beams;

(8) FIG. 4d schematically illustrate an electron beam having an elongated cross-section.

(9) FIGS. 5a-5b schematically illustrate a shaping of the liquid target in order to adjust an angle of incidence and/or a location of an interaction region;

(10) FIGS. 6a-6b schematically illustrate a movement of an electron beam in order to adjust an angle of incidence and/or a location of an interaction region.

(11) FIG. 7 is a flowchart of a method for generating X-ray radiation.

(12) The figures are not necessarily to scale, and generally only show parts that are necessary in order to elucidate the inventive concept, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

(13) An X-ray source according to the inventive concept will now be described with reference to FIG. 1a. An electron beam 100 is generated from an electron source 102, such as e.g. an electron gun comprising a high-voltage cathode, and a liquid target 104 is provided from a liquid target source 106. The electron beam 100 is directed towards an impact portion of the liquid target 104 such that the electron beam 100 interacts with the liquid target 104 and X-ray radiation 108 is generated. The liquid target 104 is preferably collected and returned to the liquid target source 106 by means of a pump 110, such as a high-pressure pump adapted to raise the pressure to at least 10 bar, preferably to at least 50 bar, for generating the liquid target 104.

(14) The liquid target 104, i.e. the anode, may be formed by the liquid target source 106 comprising a nozzle through which a fluid, such as e.g. liquid metal or liquid alloy, may be ejected to form the liquid target 104. It should be noted that it is to be understood that an X-ray source comprising multiple liquid targets, and/or multiple electron beams, is possible within the scope of the inventive concept.

(15) Still referring to FIG. 1a, the X-ray source may comprise an X-ray window (not shown) configured to allow X-ray radiation, generated from the interaction of the electron beam 100 and the liquid target 104, to be transmitted. The X-ray window may be located substantially perpendicular to a direction of travel of the electron beam.

(16) Referring now to FIG. 1b, a magnetic field generator 103 is shown in relation to the liquid target source 106 and the liquid target 104. The magnetic field generator 103 and the liquid target 104 may be comprised in an X-ray source that may be similarly configured as the X-ray source discussed in connection with FIG. 1a. It is to be understood that the magnetic field generator 103 may extend further along the flow axis, and that the placement of the magnetic field generator 103 shown is merely an example among several different configurations. In the present example, the magnetic field generator 103 may comprise a plurality of means for generating a magnetic field for modifying or shaping a cross section of the liquid target 104. Examples of such means may e.g. include electromagnets, which e.g. may be arranged at different sides of a path of the liquid target 104 so as to affect its shape.

(17) Referring now to FIG. 2, an example of a liquid target 204 moving along a flow axis F is illustrated. The liquid target is generated by the liquid target source 206. The X-ray source comprises a liquid target shaper, e.g. a nozzle 212 having a non-circular opening, in order to shape the liquid target 206 to comprise a non-circular cross section 214. In the illustrated example, the nozzle 212 has an elliptical opening. The non-circular cross section 214 has a first width, also referred to as diameter, along a first axis A.sub.1 and a second width, or diameter, along a second axis A.sub.2, wherein the first diameter is shorter than the second diameter. The liquid target 204 comprises an impact portion 216 being intersected by the first axis A.sub.1. Here, the impact portion 216 is illustrated as a uniform area centered around the first axis A.sub.1. However, it is to be understood that the impact portion 216 may have any arbitrary shape. Further, it should be noted that the impact portion 216 is here only illustrated in the non-circular cross section, although it is possible for the impact portion 216 to extend along the flow axis F.

(18) An electron beam 200 is directed towards the impact portion 216, such that the electron beam 200 interacts with the liquid target 206 and X-ray radiation is generated. In particular, the electron beam 200 is directed to an interaction region 218 located within the impact region 216. The interaction region may be defined as a region wherein X-rays are generated when hit by the electron beam.

(19) Depending on the properties of the liquid target 204, as discussed earlier in the present disclosure, axis switching may be observed. In FIG. 2, it can be seen that the first and second axis switch places along the flow axis F. The axes of the liquid target 204, i.e. the first axis A.sub.1 and the second axis A.sub.2, may switch places several times along the flow axis F, with a wavelength being proportional to a velocity of the liquid target along the flow axis F. In particular, the wavelength of axis switching is proportional to the square root of the Weber number, which corresponds to a linear velocity dependence. For certain parameter combinations situations where only one axis switch event occurs may be observed, e.g. a liquid target ejected from an elongated nozzle turns 90 degrees and then continues without turning over the observable distance.

(20) Referring now to FIG. 3, a non-circular cross section 314 is illustrated in detail. The non-circular cross section 314 may form part of a liquid target of an X-ray source similar to the ones discussed above in connection with FIGS. 1 and 2. It should be noted that the interaction region 318 is not necessarily drawn to scale in this figure. The non-circular cross section 314 comprises a first diameter 322 along a first axis A.sub.1, and a second diameter 320 along a second axis A.sub.2, wherein the first diameter 322 is shorter than the second diameter 320. The impact portion 316 as can be seen is being intersected by the first axis A.sub.1. The electron beam 200 here interacts with the liquid target at an angle of incidence θ greater than 0 degrees.

(21) Referring now to FIG. 4a, an electron beam 400 is shown interacting with a liquid target 404 at an angle of incidence θ.sub.1. The interaction region 418 is located within the impact portion 416. In order to adjust the angle of incidence and/or the location of the interaction region 418, the electron source (not shown) providing the electron beam 400 may be rotated with respect to the flow axis. As shown in FIG. 4b, such a rotation may result in the electron beam 400 interacting with the liquid target 404 at an angle of incidence θ.sub.2, and the location of the interaction region 418 may also be changed within the impact portion 416.

(22) Referring now to FIG. 4c, a first and a second electron beam 400, 401 are shown interacting with a liquid target 404. Respective first and second interaction regions 418, 419 are illustrated. The first and second interaction regions 418, 419 are arranged within the impact portion 416. X-ray radiation 408 generated in the first interaction region 418 is transmitted through a first X-ray window 421 located substantially perpendicular to the direction of the first electron beam 400. X-ray radiation 409 generated in the second interaction region 419 is transmitted through a second X-ray window 423 located substantially perpendicular to the direction of the second electron beam 401. As can be seen, X-ray radiation may preferably be transmitted via an X-ray window located in a direction pointing away from the first axis of the non-circular cross section with respect to the interaction region in which the X-ray radiation is generated. This is to avoid dampening of the X-ray radiation caused by absorption in the liquid target.

(23) Referring now to FIG. 4d, an electron beam 400 having an elongated cross-section is illustrated. The interaction region 418 located within the impact portion 416 may thus assume an elongated or line shape as seen in the illustrated cross-section. When utilizing an electron beam 400 having an elongated cross-section, it may be advantageous to direct the electron beam 400 towards the impact portion, according to the inventive concept, in order to achieve improved focal properties. Further, X-ray radiation generated in the interaction region 418 may be transmitted via X-ray windows located on either or both sides of the first axis.

(24) Referring now to FIG. 5a, an electron beam 500 is shown interacting with a liquid target 504 at an angle of incidence θ.sub.1. The interaction region 518 is located within the impact portion 516. In order to adjust the angle of incidence and/or the location of the interaction region 518, the liquid target 504 may be rotated around the flow axis. This may be achieved by e.g. rotating the nozzle around the flow axis, and/or by adjusting a magnetic field arranged to shape the liquid target 504 to comprise the non-circular cross section. As shown in FIG. 5b, a rotation of the liquid target 504 around the flow axis may result in the electron beam 500 interacting with the liquid target 504 at an angle of incidence θ.sub.2, and the location of the interaction region 518 may also be changed within the impact portion 516.

(25) Referring now to FIG. 6a, an electron beam 600 is shown interacting with a liquid target 604 at an angle of incidence θ.sub.1. Here, θ.sub.1 is substantially zero. The interaction region 618 is located within the impact portion 616. In order to adjust the angle of incidence and/or the location of the interaction region 616, the electron beam 600 may be moved along the flow axis and/or in a direction perpendicular to the flow axis. The illustrated example shows a movement of the electron beam 600 in a direction perpendicular to the flow axis. The movement of the electron beam 600 along the flow axis and/or in a direction perpendicular to the flow axis may be achieved by having an electron optics arrangement (not shown) configured to move the electron beam 600. The term “move” should be interpreted to comprise focusing, and/or deflecting the electron beam. As shown in FIG. 6b, moving the electron beam 600 as disclosed above may result in the electron beam 600 interacting with the liquid target 604 at an angle of incidence θ.sub.2, and the location of the interaction region 618 may also be changed within the impact portion 616.

(26) Further, although not illustrated, it may be possible to move the nozzle of the liquid target shaper along the flow axis, and/or adjusting a magnetic field generated by a magnetic field generator, in order to adjust the angle of incidence and/or the location of the interaction region. The resulting adjustment of the angle of incidence and/or the location of the interaction region is similar to what has been disclosed above in conjunction to FIGS. 4a-6b.

(27) Further, it is to be understood that any of combination of the adjustments disclosed above in conjunction with FIGS. 4a-6b is possible within the scope of the inventive concept.

(28) By providing suitable sensor means and a controller (not shown) the adjustments disclosed above in conjunction with FIGS. 4a-6b may be performed to achieve a desired performance. One example is to provide increased X-ray flux at a sample position, as measured by the number of X-ray photons per second. Another example is to provide increased X-ray brightness, i.e. number of photons per time, area and solid angle. To measure the brightness a detector capable of registering the spatial distribution of X-ray radiation intensity may be required. The adjustments may be controlled by a suitable control algorithm, e.g. a PID controller.

(29) As previously mentioned in connection with FIG. 4c, the X-ray source may comprise more than one electron beam, thus providing more than one interaction region. One example of this would be a dual port source, i.e. when there are two X-ray windows at opposite directions substantially perpendicular to two substantially parallel electron beams. With this arrangement the two spots may be adjusted individually to achieve the desired performance. Another example is to provide multiple X-ray sources radiating in the same direction for interferometric applications, e.g. Talbot-Lau interferometry. In this context one may note that a wide target may be preferable since the thermal load can be distributed over the width with a multiple of spots distributed substantially perpendicularly to the flow axis interacting with the liquid target. If, instead, the spots were arranged along the flow axis the allowed thermal load would be less since the downstream interaction regions would be exposed to the thermal load of the upstream interaction regions as well.

(30) A method for generating X-ray radiation according to the inventive concept will now be described with reference to FIG. 7. For clarity and simplicity, the method will be described in terms of ‘steps’. It is emphasized that steps are not necessarily processes that are delimited in time or separate from each other, and more than one ‘step’ may be performed at the same time in a parallel fashion.

(31) In step 724, a liquid target moving along a flow axis is provided. In step 726, an electron beam is provided. In step 728, the liquid target is shaped to comprise a non-circular cross section with respect to the flow axis, wherein the non-circular cross section comprises a first diameter that is shorter than a second diameter, and wherein the liquid target comprises an impact portion being intersected by the first axis. In step 730 the electron beam is directed towards the impact portion such that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation.

(32) The method may further include steps for adjusting the impact portion to provide a wider impact portion for the electron beam to interact with. The width of the liquid target may be measured by scanning 732 the electron beam across the liquid target and measuring a current absorbed in an e-dump (not shown) located downstream of the liquid target in the direction of the electron beam. Steps for controlling 734 the width towards a desired value may further be included.

(33) Alternatively, or additionally the method may include steps for measuring 736 an X-ray output, such as e.g. X-ray flux or X-ray brightness, and controlling 738 the generation of the X-ray radiation based on the measured X-ray output.

(34) The person skilled in the art by no means is limited to the example embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. In particular, X-ray sources and systems comprising more than one liquid target are conceivable within the scope of the present inventive concept. Furthermore, X-ray sources of the type described herein may advantageously be combined with X-ray optics and/or detectors tailored to specific applications exemplified by but not limited to medical diagnosis, non-destructive testing, lithography, crystal analysis, microscopy, materials science, microscopy surface physics, protein structure determination by X-ray diffraction, X-ray photo spectroscopy (XPS), critical dimension small angle X-ray scattering (CD-SAXS), and X-ray fluorescence (XRF). Additionally, variation to the disclosed examples can be understood and effected by the skilled person in practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

LIST OF REFERENCE SIGNS

(35) 100 Electron beam 102 Electron source 103 Magnetic field generator 104 Liquid target 106 Liquid target source 108 X-ray radiation 110 Pump 200 Electron beam 204 Liquid target 206 Liquid target source 212 Nozzle 214 Non-circular cross section 216 Impact portion 218 Interaction region 300 Electron beam 314 Liquid target 316 Impact portion 318 Interaction region 320 Second width 322 First width 400 First electron beam 401 Second electron beam 404 Liquid target 408 X-ray radiation 409 X-ray radiation 416 Impact portion 418 First interaction region 419 Second interaction region 421 First X-ray window 423 Second X-ray window 500 Electron beam 504 Liquid target 516 Impact portion 518 Interaction region 600 Electron beam 604 Liquid target 616 Impact portion 618 Interaction region 724 Step of providing a liquid target 726 Step of providing an electron beam 728 Step of shaping the liquid target 730 Step of directing the electron beam 732 Step of scanning the electron beam 734 Step of controlling a width 736 Step of measuring an X-ray output 738 Step of controlling the X-ray output