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

Abstract

The concept of the present invention 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 form a liquid target having a non-circular cross-section with respect to the flow axis—the non-circular cross-section having 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 the liquid target includes an impact portion intersected by the first axis—and the X-ray source is configured to direct the electron beam toward the impact portion so that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation.

Description

Technology Field

[0001] The concept of the invention as described herein generally relates to an electron shock X-ray source and a liquid target for use in such an X-ray source. Background Technology

[0002] A system for generating X-rays by irradiating a liquid target is described in the applicant’s international applications PCT / EP2012 / 061352 and PCT / EP2009 / 000481. In these systems, an electron gun comprising a high-pressure cathode is used to generate an electron beam that strikes a liquid jet. The target is preferably formed of a liquid metal having a low melting point, such as indium, tin, gallium lead, or bismuth, provided inside a vacuum chamber. Means for providing the liquid jet may include a heater and / or cooler, a pressurizing means (such as a mechanical pump or a source of a chemically inert propellant gas), a nozzle for collecting the liquid at the end of the jet, and a receptacle. X-ray radiation generated by the interaction between the electron beam and the liquid jet may leave the vacuum chamber through a window that separates the vacuum chamber from the surrounding atmosphere.

[0003] However, an improved X-ray source is still needed.

[0004] The objective of the concept of the present invention is to provide an improved X-ray source.

[0005] According to a first aspect of the concept of the present invention, an X-ray source is provided to include: a liquid target source configured to provide a liquid target that moves along a flow axis; an electron source configured to provide an electron beam; and a liquid target shaper configured to form the liquid target to include a non-circular cross section with respect to the flow axis—the non-circular cross section has a first width along a first axis and a second width along a second axis, the first width being shorter than the second width, and the liquid target including a shock portion intersected by the first axis—and the X-ray source is configured to direct the electron beam toward the shock portion so that the electron beam interacts with the liquid target within the shock portion to generate X-ray radiation, and the X-ray source further comprises a device configured to move the position where the electron beam interacts with the liquid target within the shock portion.

[0006] The concept of the present invention is based on the recognition that, by providing a liquid target having a non-circular cross-section, a wider impact surface for an electron beam can be achieved, for example, without increasing the flow rate of the liquid target. A wider or less curved impact surface also enables multiple electron beams to simultaneously impact the liquid target, preferably along a direction perpendicular to the flow axis, and allows for the use of larger or wider electron beam spots without substantially impairing the focus of the X-ray spot. It will be understood that such an impact surface can also be used with electron beam spots that are elliptical or even linear in shape.

[0007] Furthermore, liquid targets with non-circular cross-sections can provide improved thermal properties compared to corresponding liquid targets with circular cross-sections having similar widths and flow rates. In particular, by reducing the width along one of the axes defining the cross-section of the liquid target, the velocity of the liquid target can be increased, thereby improving its thermal properties. In other words, the ability to thermally load the liquid target varies depending on the velocity of the liquid target. Maintaining velocity while increasing the width implies increasing the mass flow, which can make the requirements for the pump system more demanding.

[0008] It is also desirable to be able to adjust the position of the impact part with respect to the position of the electron source and / or X-ray window through which the X-ray radiation can exit the X-ray source. Preferably, the impact part and the electron source can be aligned so that the electron beam strikes the largest surface portion of the liquid target, that is, the portion of the liquid target having the smallest curvature. Additionally, it may be desirable to increase the width of the target at the impact part to provide a larger surface area for the electron beam to strike.

[0009] Additionally, it has been recognized that the angle of incidence of the electron beam striking the liquid target may be important, for example, to the spatial distribution of the generated X-ray radiation. In particular, the angle of incidence of the electron beam striking the liquid target and / or the position where the electron beam strikes the liquid target can be selectively adjusted by rotating the first axis of the cross-section with respect to the direction of the electron beam, or vice versa, and / or can be selectively adjusted by adjusting the position where the electron beam strikes the liquid target.

[0010] In the context of the present application, the term “width” may refer to the left-right diameter or range of a liquid target. In particular, the first width may be the largest width of a non-circular cross-section along the first axis, and the second width may be the largest width of a non-circular cross-section along the second axis. The first and second axes may be orthogonal to each other and may intersect with the flow axis. The second width may be 100 μm, for example, 10 μm to 1000 μm, for example, 100 μm to 500 μm, for example, 150 μm to 250 μm. The ratio between the second width and the first width may be at least 1.05, such as at least 1.1, at least 1.5, at least 2, or at least 5 in some examples.

[0011] The term 'liquid target' may refer, in the context of this application, to a stream or flow of liquid that is forced to pass through, for example, a nozzle and propagate through a system for generating X-rays. While the liquid target may generally be formed as an essentially continuous flow or stream of liquid, it will be understood that the liquid target may additionally or otherwise comprise a plurality of droplets or even be formed as droplets. In particular, droplets may be generated when interacting with an electron beam. Such examples of groups or clusters of droplets may also be included by the term 'liquid target'.

[0012] Liquid targets can have non-circular cross-sections, which may be suitable for oval, elliptic, or other elongated shapes. By making the cross-section longer, the surface curvature at the impact zone can be reduced. Ultimately, the curvature can be low enough so that the surface of the impact zone approximates a flat two-dimensional surface. Such targets may also be referred to as 'flat jets'. In other words, the location of the impact zone can be selected as a part of the liquid target that most closely resembles a flat surface. A liquid curtain is an extreme example of such a jet, representing a substantially flat surface that can be used as an impact zone for an electron beam.

[0013] The liquid target can be formed into a liquid jet that propagates freely with respect to the surrounding environment at least at the location of the impact area. Accordingly, the material of the liquid jet can be exposed to the environment inside the chamber of the X-ray source.

[0014] Typically, the liquid target material is preferably a metal having a relatively low melting point. Examples of such metals include indium, gallium, tin, lead, bismuth, and alloys thereof.

[0015] As further described in the disclosure below, the electron beam spot of the electron beam may have a circular or elongated shape. In some examples, the elongated shape may also be realized as a linear shape or a linear focus. In the case of a linear focus, an aspect ratio, that is, the ratio between the focal width and the focal height, may be defined. A typical value of the aspect ratio that can be achieved on a liquid target having a circular cross-section is 4. A liquid target having a non-circular cross-section may enable a larger aspect ratio, for example, at least 6. The shape of the electron beam spot may be selected according to the desired flux and / or brightness of the generated X-ray radiation.

[0016] To fully understand the following disclosure, for a sufficiently large Weber number, a phenomenon called axial switching can be observed for a liquid target emerging from a nozzle having a non-circular opening. Axial switching evolves in such a way that the major and minor axes of the cross-section of a non-circular liquid, such as an elliptical one, periodically switch positions along the flow direction of the liquid target. As the liquid target velocity increases, the wavelength of the switching increases. Furthermore, axial switching is attenuated by viscosity, which means that as viscosity increases, the amplitude of the axial switching approaches zero.

[0017] Consequently, it should be understood that the impact portion may extend along the flow axis. Additionally, the impact portion may be described as a portion within a sector of a non-circular cross-section. This portion may be a span sector having an angle of, for example, 120 degrees or less, 90 degrees or less, 60 degrees or less, or 180 degrees or less, and preferably may be centered around a first axis.

[0018] The X-ray source may be further configured to direct the electron beam toward a specific region within the impact part. This region may also be referred to as the interaction region. Thus, while the impact part can be understood as a portion such as a surface portion or volume intersected by a first axis, the interaction region can be understood as a specific portion or region of the impact part where X-ray radiation struck by the electron beam may be generated. The interaction region may be a volume extending a distance toward the center of a non-circular cross-section, i.e., toward the flow axis. Likewise, the impact part may be a volume and may extend a distance toward the center of a non-circular cross-section, i.e., toward the flow axis.

[0019] As is readily understood from the present disclosure, the device may be configured to adjust the location where the electron beam strikes the liquid target, or in other words, the location of the interaction region. This may be necessary to allow the entire size of the electron beam spot to interact with the liquid target, and in particular to allow the electron beam spot to interact with the liquid target within the impact portion.

[0020] This device may include, for example, an electron-optical device for moving an electron beam relative to a liquid target. Alternatively, or additionally, this device may be configured to work in cooperation with a liquid target shaper to move or adjust the position where the electron beam interacts with the target. In one example, this device may include a motor or actuator coupled to the liquid target shaper and positioned to move the target shaper in such a way that the position or orientation of the liquid target can be adjusted. This device may be configured, for example, to rotate the liquid target shaper around a flow axis, thereby causing a corresponding rotation of the impact part around the flow axis so that the orientation and / or position of the impact part relative to the electron source can be changed. In another example, this device may be configured to move the liquid target shaper in a direction orthogonal to the flow axis and / or the trajectory of the electron beam and / or to tilt the liquid target shaper with respect to the flow axis.

[0021] In one example, the device may be configured to control a magnetic field generator configured to generate a magnetic field to form a liquid target having a non-circular cross-section. The magnetic field generator will be described in more detail below.

[0022] The above disclosure provides several examples of how a device may be utilized to adjust the relative position between an electron beam and a liquid target. The angle of incidence of the electron beam may be adjusted by moving the interaction region and / or impact portion. The purpose of such modification may be to increase the total X-ray flux along the direction of observation or at the sample location, to increase the brightness of the X-ray source, or to align the position of the X-ray source equipped with other parts of the X-ray system (e.g., optics). In one example, the adjustment of the angle of incidence and / or the position of the interaction region is based on the measured X-ray output.

[0023] The electron beam can interact with the impact part at an angle of incidence that can be greater than 0 degrees. The angle of incidence can be defined as the angle of incidence relative to the normal of a non-circular cross section.

[0024] The advantage of having an electron beam interacting with the impact part at an angle of incidence greater than 0 degrees is that less X-ray can be absorbed by the liquid target. In particular, more X-rays can be delivered through an X-ray window positioned at an angle substantially perpendicular to the direction of the electron beam. As a result, the device can provide increased total X-ray flux and / or increased X-ray brightness.

[0025] In the following, among other things, possible modifications to the X-ray source will be followed to provide adjustment of the angle of incidence at which the electron beam strikes the liquid target and / or the position of the interaction region. As can be understood from the following paragraph, the modification may relate to the liquid target, the electron beam, or a combination of both.

[0026] The electron source may be configured to rotate around a flow axis to adjust the angle of incidence of the electron beam and / or the position of the interaction region where the electron beam strikes the target.

[0027] A liquid target shaper may include a nozzle having a non-circular opening to form a liquid target that includes a non-circular cross-section. The opening may have a shape selected from a group including, for example, elliptical, rectangular, square, hexagonal, elliptical, stadium, and rectangular with rounded corners.

[0028] It will be understood that an X-ray source according to some embodiments may be configured to move a liquid target relative to the electron beam to change the location where the electron beam interacts with the liquid target. The movement may be realized, for example, in a direction orthogonal to the flow axis of the liquid jet and / or in a direction orthogonal to the propagation direction of the electron beam, so that a lateral shift in the location of the interaction region occurs. The movement or shift in the location of the interaction region may be achieved, for example, by a liquid target source.

[0029] In one example, the nozzle of the liquid target source may be configured to move along the flow axis to adjust the angle of incidence and / or the position of the interaction region.

[0030] In one example, the nozzle may be configured to rotate around a flow axis to adjust the angle of incidence and / or the position of the interaction region.

[0031] In one example, the liquid target source may be configured to move in a direction perpendicular to the flow axis to adjust the angle of incidence and / or the position of the interaction region.

[0032] A liquid target shaper may include a magnetic field generator configured to generate a magnetic field to form a liquid target that includes a non-circular cross-section. The magnetic field may be substantially perpendicular to the flow axis. The magnitude of the magnetic field may be non-uniform in the direction of the flow axis, so that the liquid target may experience a field gradient as it moves along the flow axis. In other words, the magnetic field may include a magnetic field gradient. The mechanism for forming the liquid target may be based on vortices induced within the liquid target and may therefore be electrically conductive. The magnetic field may be an alternating magnetic field.

[0033] An example may include a time-varying component of a magnetic field directed along the flow axis. This field component can impart acceleration to the liquid target, thereby increasing the thermal load that can be applied to the liquid target before vaporization or similar problems occur.

[0034] The maximum relative change in the liquid target radius due to the application of a magnetic field gradient

[0035]

[0036] It can be written as follows.

[0037] Here, And, is, And, is,

[0038] am.

[0039] As defined above It is called the Stewart number, and is the Weber number, and α is the nozzle radius, and is the magnitude of the magnetic field, and is the length scale of the magnetic field gradient, and is the electrical conductivity of the liquid target.

[0040] In one example, the liquid target is made of liquid gallium, and the following value is entered into the above mathematical formula.

[0041] ρ = 6100 kg / m 3 ,

[0042] σ = 0.7 N / m,

[0043] α = 100 μm,

[0044] = 100 m / s,

[0045] = 4 MS / m,

[0046] = 1.7 T,

[0047] = 1 mm, and

[0048] This can reduce the maximum change in the liquid target radius by a small percentage.

[0049] Similar to the case of an elliptical nozzle, the shape of the liquid target can vibrate along the flow axis. The value used above provides a nozzle radius of approximately 250, or a wavelength of 25 mm. If the exit velocity of the liquid target increases to 1000 m / s (i.e., the Weber number increases 100-fold), the amplitude remains nearly the same, but the wavelength increases tenfold. Since the magnitude scales according to the Stewart number, that is, the square of the magnetic field, one way to increase the magnitude of the relative radius change is to increase the magnetic field. Another way to enhance the effect is to increase the Weber number. This can be done without affecting the Stewart number by reducing surface tension. This can also be achieved by increasing the temperature. For example, by increasing the magnetic field to 4 T, the magnitude of the effect is approximately 10% of the relative radius change. For reference, the magnitude can also increase as the nozzle diameter increases. However, as discussed above, this can be counterproductive because increasing the diameter alone can slow down the velocity if mass flow is maintained. A slower velocity may result in a lower permissible thermal load on the liquid target.

[0050] The magnetic field generator may be configured to adjust the magnetic field to adjust the angle of incidence and / or the position of the interaction region.

[0051] The magnetic field may be non-uniform. In particular, the magnetic field generator may be configured to adjust the direction of the non-uniform magnetic field to adjust the angle of incidence and / or the location of the interaction region.

[0052] In one example, the magnetic field generator may be configured to generate a magnetic field that moves a liquid target such that the position of the interaction region is moved relative to the electron beam.

[0053] The liquid target source may be configured to provide an adjustable flow rate of the liquid target to adjust the first and second widths.

[0054] The liquid target can be a metal.

[0055] The X-ray source can be configured to rotate the impact area with respect to the direction of the electron beam. In other words, the X-ray source can be configured to rotate the first axis of a non-circular cross-section with respect to the direction of the electron beam.

[0056] It should be understood that the nozzle and magnetic field generator as described above may all be present in the X-ray source according to the concept of the present invention.

[0057] According to a second aspect of the concept of the present invention, a method for generating X-ray radiation is provided. The method comprises the steps of: providing an electron beam; providing a liquid target moving along a flow axis ― the liquid target comprises a non-circular cross section with respect to the flow axis, the non-circular cross section has a first width along a first axis and a second width along a second axis, the first width being shorter than the second width, and the liquid target comprises an impact portion intersected by the first axis ―; and directing the electron beam toward the impact portion so that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation.

[0058] This method may further include the step of moving the electron beam along the flow axis and / or in a direction perpendicular to the flow axis to move the location where the electron beam interacts with the liquid target, i.e., the interaction region.

[0059] This method may further include a step of rotating the electron source around the flow axis to adjust the angle of incidence and / or the position of the interaction region.

[0060] This method may further include the step of moving the nozzle along the flow axis to adjust the angle of incidence and / or the position of the interaction region.

[0061] This method may further include the step of rotating the nozzle around the flow axis to adjust the angle of incidence and / or the position of the interaction region.

[0062] The step of providing a liquid target may include the step of providing a magnetic field to form a non-circular cross-section of the liquid target.

[0063] This method may further include a step of adjusting the magnetic field to adjust the angle of incidence and / or the position of the interaction region.

[0064] This method may further include a step of adjusting the flow rate of a liquid target to adjust the first and second widths.

[0065] This method may further include a step of rotating the impact area with respect to the direction of the electron beam.

[0066] This method may further include, for example, the step of scanning an electron beam between an unobscured portion of a liquid target and a sensor area, preferably an impact portion, to determine the width of the electron beam. According to a first aspect, a sensor area that may form part of an X-ray source may be positioned behind the liquid target as seen from the electron source, so that the liquid target may at least partially obscure the sensor area. Such a device allows the electron beam to be scanned into and / or outside the liquid target and to strike the unobscured portion(s) of the sensor area. Subsequently, an output signal from the sensor may be analyzed to determine the width of the liquid target, preferably in a direction perpendicular to the scanning direction or the flow axis.

[0067] The determined width of the liquid target can be used as a feedback or adjustment parameter for the operation of the liquid target source, liquid target shaper, and / or electron beam. The purpose of such feedback or adjustment may preferably be to control the width of the liquid target at the impact portion. Accordingly, the width can be changed by adjusting the flow rate of the liquid target, by rotating the impact portion around the flow axis, by moving the position where the electron beam interacts with the liquid target, and / or by adjusting the angle of incidence between the electron beam and the surface of the impact portion.

[0068] In one example, the method according to the second aspect may include measuring X-ray output, such as X-ray flux and / or X-ray brightness, for example. The measurement may be performed by sensor means for characterizing or quantifying the generated X-ray radiation. Similar to the feedback mechanism described above, the measured X-ray output may be used to control the interaction between the electron beam and the liquid target to achieve a desired output, for example, flux or brightness. The interaction may be controlled, for example, by rotating the impact part around a flow axis, moving the position where the electron beam interacts with the liquid target, or adjusting the angle of incidence between the electron beam and the surface of the impact part.

[0069] The feature described in relation to the first aspect among the above-mentioned aspects may also be incorporated into other aspects among the above-mentioned aspects, and the advantages of the feature may be applied to all aspects containing the feature.

[0070] Other objects, features, and advantages of the concept of the present invention will become apparent from the drawings, as well as from the appended claims and the following detailed description.

[0071] Generally, all terms used in the claims shall be interpreted according to their common meaning in the technical field unless otherwise clearly defined in this specification.

[0072] Additionally, the use of terms such as “first,” “second,” and “third” in this specification does not indicate any order, quantity, or importance, but is used to distinguish one element from another. Any reference to “one (a / an / the) [element, device, component, means, step, etc.]” ​​should be publicly interpreted to refer to at least one instance of the said element, device, component, means, step, etc., unless otherwise specified. Steps of any method disclosed in this specification do not need to be performed in the disclosed order unless explicitly stated otherwise. Brief explanation of the drawing

[0073] Additional objects, features, and advantages of the concept of the invention, as well as the above objects, will be better understood through the following exemplary and non-limiting detailed description of other embodiments of the concept of the invention with reference to the accompanying drawings. Figure 1a schematically illustrates an X-ray source. FIG. 1b schematically illustrates an X-ray source equipped with a magnetic field generator. FIG. 2 schematically illustrates a perspective view of a liquid target. Figure 3 schematically illustrates a non-circular cross-section of a liquid target. FIGS. 4a and 4b schematically illustrate the movement of an electron source to adjust the angle of incidence and / or the position of the interaction region. FIG. 4c schematically illustrates a non-circular cross-section of a liquid target colliding with multiple electron beams. Figure 4d schematically illustrates an electron beam having a long cross-section. FIGS. 5a and 5b schematically illustrate the shape of a liquid target to adjust the angle of incidence and / or the position of the interaction region. FIGS. 6a and 6b schematically illustrate the movement of an electron beam to adjust the angle of incidence and / or the position of the interaction region. Figure 7 is a flowchart of a method for generating X-ray radiation. The drawings are not necessarily drawn to scale and generally only show the parts necessary to explain the concept of the invention, while other parts may be omitted or simply suggested. Specific details for implementing the invention

[0074] Hereinafter, an X-ray source according to the concept of the present invention will be described with reference to FIG. 1a. An electron beam (100) is generated from an electron source (102), such as an electron gun including a high-pressure cathode, for example, and a liquid target (104) is provided from a liquid target source (106). The electron beam (100) is directed toward the impact portion of the liquid target (104) so ​​that the electron beam (100) interacts with the liquid target (104) to generate X-ray radiation (108). The liquid target (104) is preferably collected and recovered into the liquid target source (106) by a pump (110), such as a high-pressure pump configured to raise the pressure to at least 10 bar, preferably at least 50 bar, to generate the liquid target (104).

[0075] A liquid target (104), i.e., an anode, may be formed by a liquid target source (106) comprising a nozzle through which a fluid, such as, for example, a liquid metal or a liquid alloy, can be emitted to form the liquid target (104). It should be understood that a plurality of liquid targets and / or an X-ray source comprising a plurality of electron beams is possible within the scope of the concept of the present invention.

[0076] Referring still to FIG. 1a, the X-ray source may include an X-ray window (not shown) configured to transmit X-ray radiation generated from the interaction between the electron beam (100) and the liquid target (104). The X-ray window may be positioned substantially perpendicular to the direction of travel of the electron beam.

[0077] Now, referring to FIG. 1b, a magnetic field generator (103) is illustrated in relation to a liquid target source (106) and a liquid target (104). The magnetic field generator (103) and the liquid target (104) may be included in an X-ray source that can be configured similarly to the X-ray source discussed in relation to FIG. 1a. It should be understood that the magnetic field generator (103) may be further extended along the flow axis, and that the arrangement of the illustrated magnetic field generator (103) is only one example of several different configurations. In this example, the magnetic field generator (103) may include a plurality of means for generating a magnetic field to modify or form a cross-section of the liquid target (104). Examples of such means may include, for instance, an electromagnet that may be placed on the other side of the path of the liquid target (104) to influence its shape.

[0078] Now, referring to FIG. 2, an example of a liquid target (204) moving along a flow axis (F) is illustrated. The liquid target is generated by a liquid target source (206). The X-ray source includes a nozzle (212) having a non-circular opening to form the liquid target (206) to include a liquid target shaper, for example, 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 a diameter along a first axis (A1), and a second width, also referred to as a diameter along a second axis (A2), wherein the first diameter is shorter than the second diameter. The liquid target (204) includes an impact portion (216) intersected by the first axis (A1). Here, the impact portion (216) is illustrated as a uniform area centered on the first axis (A1). However, it should be understood that the impact portion (216) may have any shape. Also, it should be noted that while the impact portion (216) may extend along the flow axis (F), the impact portion (216) is shown here only as a non-circular cross-section.

[0079] The electron beam (200) is directed toward the impact area (216) so that the electron beam (200) interacts with the liquid target (206) to generate X-ray radiation. In particular, the electron beam (200) is directed toward an interaction area (218) located within the impact area (216). The interaction area can be defined as an area where X-rays are generated when struck by the electron beam.

[0080] Depending on the characteristics of the liquid target (204), axis switching may be observed, as previously discussed in the present disclosure. In FIG. 2, it can be seen that first and second axis switches are arranged along the flow axis (F). The axes of the liquid target (204), namely the first axis (A1) and the second axis (A2), may switch locations along the flow axis (F) multiple times with a wavelength proportional to the velocity of the liquid target along the flow axis (F). In particular, the wavelength of the axis switching is proportional to the square root of the Weber number corresponding to the linear velocity dependence. For a specific combination of parameters, a situation may be observed where only one axis switching event occurs. For example, a liquid target emitted from a long nozzle rotates 90 degrees and continues without exceeding an observable distance.

[0081] Now, referring to FIG. 3, a non-circular cross section (314) is illustrated in detail. The non-circular cross section (314) may form part of the liquid target of an X-ray source similar to that discussed above in relation to FIG. 1 and 2. It should be noted that the interaction region (318) is not necessarily illustrated to scale in this figure. The non-circular cross section (314) includes a first diameter (322) along a first axis (A1) and a second diameter (320) along a second axis (A2), wherein the first diameter (322) is shorter than the second diameter (320). As can be seen, the impact portion (316) intersects the first axis (A1). Here, the electron beam (200) interacts with the liquid target at an angle of incidence (θ) greater than 0 degrees.

[0082] Now, referring to FIG. 4a, the electron beam (400) is illustrated as interacting with the liquid target (404) at an angle of incidence (θ1). The interaction area (418) is located within the impact portion (416). To adjust the angle of incidence and / or position of the interaction area (418), the electron source (not illustrated) providing the electron beam (400) may be rotated about the flow axis. As illustrated in FIG. 4b, this rotation causes the electron beam (400) to interact with the liquid target (404) at an angle of incidence (θ2), and the position of the interaction area (418) may also be changed within the impact portion (416).

[0083] Now, referring to FIG. 4c, the first and second electron beams (400, 401) are illustrated as interacting with a liquid target (404). Each of the first and second interaction regions (418, 419) is illustrated. The first and second interaction regions (418, 419) are positioned 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) positioned substantially orthogonal 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) positioned substantially orthogonal to the direction of the second electron beam (401). As can be seen, the X-ray radiation may preferably be transmitted through an X-ray window positioned away from the first axis of a non-circular cross-section with respect to the interaction region where the X-ray radiation is generated. This is to avoid the attenuation of X-ray radiation due to absorption in the liquid target.

[0084] Now, referring to 4d, an electron beam (400) having a long cross-section is illustrated. Accordingly, the interaction region (418) located within the impact portion (416) can be assumed to have a long or linear shape as shown in the illustrated cross-section. When using an electron beam (400) having a long cross-section, it may be advantageous to orient the electron beam (400) toward the impact portion to obtain enhanced focusing properties according to the concept of the present invention. Additionally, X-ray radiation generated in the interaction region (418) can be transmitted through an X-ray window located on one or both sides of the first axis.

[0085] Now, referring to FIG. 5a, the electron beam (500) is illustrated as interacting with the liquid target (504) at an angle of incidence (θ1). The interaction area (518) is located within the impact portion (516). To adjust the angle of incidence and / or the location of the interaction area (518), the liquid target (504) may be rotated around a flow axis. This may be accomplished, for example, by rotating the nozzle around the flow axis and / or by adjusting the magnetic field positioned to shape the liquid target (504) to include a non-circular cross-section. As illustrated in FIG. 5b, the rotation of the liquid target (504) around the flow axis causes the electron beam (500) to interact with the liquid target (504) at an angle of incidence (θ2), and the location of the interaction area (518) may also be changed within the impact portion (516).

[0086] Now, referring to FIG. 6a, the electron beam (600) is illustrated as interacting with a liquid target (604) at an angle of incidence (θ1). Here, θ1 is substantially 0. The interaction area (618) is located within the impact portion (616). To adjust the angle of incidence and / or the location of the interaction area (616), the electron beam (600) may be moved along the flow axis and / or perpendicular to the flow axis. The illustrated example shows the movement of the electron beam (600) in a direction perpendicular to the flow axis. Movement of the electron beam (600) along the flow axis and / or perpendicular to the flow axis may be achieved by having an electron optical device (not illustrated) configured to move the electron beam (600). The term "move" should be interpreted to include focusing the electron beam and / or deflecting the electron beam. As illustrated in FIG. 6b, moving the electron beam (600) as described above allows the electron beam (600) to interact with the liquid target (604) at an angle of incidence (θ2), and the position of the interaction area (618) can also be changed within the impact portion (616).

[0087] Additionally, although not illustrated, to adjust the angle of incidence and / or the position of the interaction region, it may be possible to move the nozzle of the liquid target shaper along the flow axis and / or adjust the magnetic field generated by the magnetic field generator. The resulting adjustment of the angle of incidence and / or the position of the interaction region is similar to that disclosed above in relation to FIGS. 4a through 6b.

[0088] In addition, it should be understood that any combination of the adjustments disclosed above in relation to FIGS. 4a to 6b is possible within the scope of the present invention.

[0089] By providing appropriate sensor means and a controller (not shown), the adjustment disclosed in relation to FIGS. 4a through 6b can be performed to achieve desired performance. One example is to provide an increased X-ray flux at the sample location, as measured by the number of X-ray photons per second. Another example is to provide increased X-ray brightness, i.e., the number of photons per hour, area, and solid angle. To measure brightness, a detector capable of registering the spatial distribution of X-ray radiation intensity may be required. The adjustment can be controlled by an appropriate control algorithm, for example, a PID controller.

[0090] As previously mentioned in relation to FIG. 4c, since the X-ray source may comprise one or more electron beams, it may provide one or more interaction regions. One example of this is a dual-port source, that is, when two X-ray windows exist in opposite directions substantially perpendicular to two substantially parallel electron beams. With such a device, the two spots can be adjusted individually to achieve desired performance. Another example is providing multiple X-ray sources radiating in the same direction for interferometric applications, e.g., Talbot-Lau interferometry. In this situation, it can be seen that a wide target may be desirable because the thermal load can be distributed across the width having multiple spots distributed substantially perpendicular to the flow axis interacting with the liquid target. Conversely, if the spots are positioned along the flow axis, the allowable thermal load will be lower because the downstream interaction region is also exposed to the thermal load of the upstream interaction region.

[0091] Hereinafter, a method for generating X-ray radiation according to the concept of the present invention will be described with reference to FIG. 7. For clarity and simplicity, this method will be described as 'steps'. Steps do not necessarily have to be processes that are temporally separated or separated from one another, and one or more 'steps' may be performed simultaneously in parallel.

[0092] 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 formed to include a non-circular cross-section with respect to the flow axis, wherein the non-circular cross-section includes a first diameter shorter than a second diameter, and the liquid target includes an impact portion intersected by the first axis. In step 730, the electron beam is directed toward the impact portion so that the electron beam interacts with the liquid target within the impact portion to generate X-ray radiation.

[0093] This method may further include a step of adjusting the impact area to provide a wider impact area for the electron beam to interact. The width of the liquid target can be measured by scanning (732) the electron beam across the liquid target and measuring the current absorbed by an e-dump (not shown) located downstream of the liquid target in the direction of the electron beam. A step (734) of controlling the width to a desired value may further be included.

[0094] Alternatively or additionally, this method may include a step (736) of measuring an X-ray output, such as an X-ray flux or X-ray brightness, for example, and a step (738) of controlling the generation of X-ray radiation based on the measured X-ray output.

[0095] Those skilled in the art are by no means limited to the exemplary 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 one or more liquid targets may be conceived within the scope of the concept of the present invention. Furthermore, X-ray sources of the types described herein may advantageously be combined with X-ray optics and / or detectors tailored to specific applications exemplified by medical diagnostics, non-destructive testing, lithography, crystal analysis, microscopy, materials science, microscopic surface physics, protein structure determination by X-ray diffraction, X-ray photospectroscopy (XPS), critical dimension small angle X-ray scattering (CD-SAXS), and X-ray fluorescence (XRF), but are not limited thereto. Additionally, variations of the disclosed examples may be understood and influenced by those skilled in the art when practicing the claimed invention from the study of the drawings, the disclosures, and the appended claims. The fact that specific measurements are cited in different dependent claim scopes does not indicate that a combination of these measurements cannot be used to one's advantage. Explanation of the symbols

[0096] 100 electron beams 102 Electronic Sources 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 nozzles 214 Non-circular cross-section 216 Impact part 218 Interaction Area 300 electron beam 314 Liquid Target 316 Impact part 318 Interaction Area 320 2nd width 322 1st width 400 First Electron Beam 401 Second Electron Beam 404 Liquid Target 408 X-ray radiation 409 X-ray radiation 416 Impact part 418 First Interaction Zone 419 Second Interaction Zone 421 First X-ray Window 423 Second X-ray Window 500 electron beam 504 Liquid Target 516 Impact Part 518 Interaction Area 600 electron beam 604 Liquid Target 616 Impact Part 618 Interaction Area 724 Step of providing a liquid target Step of providing 726 electron beam 728 Step of forming a liquid target 730 electron beam aiming stage 732 Step of scanning the electron beam 734 Step to control width 736 Step to measure X-ray output 738 Steps to control X-ray output

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