Characterization of electron beams

Abstract

A method for characterizing an electron beam in a liquid metal jet X-ray source is disclosed. The method includes providing an electron beam and directing the electron beam toward an interference region, providing an electron beam dump connected to ground potential to receive the electron beam after it traverses the interference region, scanning the electron beam over at least a portion of the interference region, measuring X-ray radiation generated by interaction between the electron beam and the electron beam dump during the scan to obtain an X-ray profile, and calculating electron beam properties based on the X-ray profile. A corresponding liquid metal jet X-ray source is also disclosed.

Description

【Technical Field】 【0001】 The present invention disclosed herein generally relates to the characterization of electron beams in liquid metal jet X-ray sources. 【Background Art】 【0002】 X-ray radiation can be generated by colliding an electron beam with a target material. X-ray radiation can be generated as bremsstrahlung or characteristic line radiation from the target material. The performance of an X-ray source depends, inter alia, on the characteristics of the focal spot of the X-ray radiation generated by the interaction between the electron beam and the target. Generally, there is an effort towards higher brightness and smaller focal spots of X-ray radiation, which requires improved control of the interaction between the electron beam and the target. In particular, several attempts have been made to more accurately determine and control the spot size and shape of the electron beam impinging on the target. 【0003】 WO2012 / 087238 discloses a technique for determining and controlling the width of an electron beam at the interaction point with a target. This prior art involves the use of a sensor having a charge-sensitive area. The measurement of the beam width is performed by deflecting the electron beam on the sensor area while an electron target is present and partially obscuring the sensor area. Since the electron target obscures or partially obscures a part of the sensor area, the recorded sensor signal shows the transition between the minimum attenuation (unobscured sensor area) and the maximum attenuation (behind the target) of the beam. The beam width can be derived from this information, particularly from the width of the transition. However, for measurement purposes, the sensor area cannot be electrically grounded. Thus, this technique involves problems such as how to avoid short circuits and arc discharges at the sensor edges. 【Summary of the Invention】 【0004】 This invention provides an improvement to an electron beam impacted liquid metal jet X-ray source and is based on the idea of ​​characterizing an electron beam by measuring the X-ray emission generated by the electron beam. More specifically, the generated X-ray emission can be measured while scanning the electron beam to obtain an X-ray profile. Then, one or more properties of the electron beam can be calculated based on the obtained X-ray profile. 【0005】 Therefore, in embodiments of the present invention, the characteristics of the electron beam are determined by detecting the X-ray emission generated from the electron beam during its scan. Since it is not necessary to measure the current passing through the portion of the X-ray source ("electron dump") into which the electron beam collides after crossing the interference region, this portion can be connected to ground (i.e., electrically grounded). By relying on X-ray measurements instead of current measurements, the electron beam dump does not need to be electrically isolated from its surroundings, thereby eliminating the risk of short circuits due to the deposition of material droplets from a liquid jet at the edges of the electron dump, for example. Furthermore, image distortion caused by the deposition of droplets on the electron dump surface can be significantly reduced, since such deposition material is typically either transparent to X-rays depending on its configuration or acts as another X-ray source. 【0006】 One characteristic of an electron beam of interest is its cross-sectional expansion (width). The width or cross-sectional expansion of an electron beam can be appropriately defined as the full width at half maximum (FWHM). This is sometimes referred to as the beam's "spot size." The width of the electron beam in the interference region where it collides with a liquid metal jet target is a critical factor affecting the X-ray generation process. Embodiments of the present invention can be used to determine the width of the electron beam in the interference region by using a liquid metal jet as an obscuring object through which the electron beam is scanned, or by scanning the electron beam across the interference region and passing the electron beam through the aperture before detection. In the latter case, the width of the electron beam is determined at the aperture, and then the width in the interference region is mathematically determined through a direct geometric transformation. Other characteristics of the electron beam may include, for example, its intensity profile and alignment. 【0007】 In some embodiments of the present invention, a liquid metal jet is used as an object that obscures the electron beam from an electron beam dump. The electron beam is scanned between a first position where the electron beam collides with the electron beam dump, which is not obscured by the liquid metal jet, a second position where the liquid metal jet obscures the electron beam dump to the greatest extent, and an appropriate set of intermediate positions. The X-ray emission generated by the interaction between the electron beam and the electron beam dump is measured during the scan to obtain an X-ray profile that maps the scan position to the generated X-ray emission, i.e., the X-ray profile can be considered a function of the deflection setting during the scan. Thus, the transition between the unobscured position and the obscured position can be identified, and the width of such a transition corresponds to the width of the electron beam measured in the liquid metal jet. As can be understood, the width determined with respect to the scan position can be readily converted to units of length, given that the displacement of the electron beam in the liquid metal jet is known for each scan position. 【0008】 In embodiments where an electron beam is scanned over a liquid metal jet, the distance required to move the beam from one side of the jet to the other can be considered a measure of the width of the liquid metal jet itself. Furthermore, the position of the liquid metal jet can be obtained from the position where the electron beam is obscured by the liquid metal jet. Variations in the width and / or position of the liquid metal jet can be considered as an indicator of the stability of the process generating the liquid metal jet. 【0009】 In some embodiments, the scan can be performed between a first position where at least half of the electron beam passes through a first side of the liquid metal jet before impacting the electron beam dump, and a second position where at least half of the electron beam passes through a second side of the liquid metal jet before impacting the electron beam dump. The width of the electron beam can then be extracted from the change in X-ray emission generated as the electron beam is scanned from the first side to the other. In this way, the electron beam width can be measured to exceed the width of the liquid metal jet. 【0010】 In some embodiments, covering objects other than liquid metal jets are used. Various covering objects can be used, provided that they absorb and / or reflect electrons so that electrons do not reach the electron beam dump. 【0011】 In other embodiments, the X-ray profile is determined not only by the X-ray emission generated by the interaction between the electron beam and the electron beam dump, but also by the interaction between the electron beam and the liquid metal jet itself. In such embodiments, the electron beam dump primarily functions as a feature for charge disposal. The X-ray emission generated by the interaction between the electron beam and the liquid metal jet during electron beam scanning is measured using an X-ray detector. As is understood, the X-ray detector can detect X-ray emission when the electron beam collides with the liquid metal jet, but does not detect X-ray emission when the electron beam does not collide with the liquid metal jet. At a certain scanning position of the electron beam, the generation of X-ray emission is maximum, and as described above, the width of the electron beam can be determined from the relationship between the scanning position and the detected X-ray emission, i.e., from the X-ray profile. 【0012】 In some embodiments, the generated X-ray emission passes through a pinhole before being detected by an X-ray detector. Such use of a pinhole provides imaging capabilities that can be used to determine properties such as cross-sectional expansion of the electron beam. 【0013】 Accordingly, the methods and devices described in the independent claims are provided. The dependent claims define advantageous embodiments of the present invention. [Brief explanation of the drawing] 【0014】 Embodiments of the disclosed invention will be described in the following detailed description with reference to the accompanying drawings. [Figure 1] Figure 1 is a flowchart illustrating the method according to the present invention. [Figure 2] Figure 2 is a schematic perspective view of a liquid metal jet X-ray source according to several embodiments of the present invention. [Figure 3] Figure 3 schematically shows a first embodiment of the liquid metal jet X-ray source according to the present invention. [Figure 4]Figure 4 schematically shows a second embodiment of the liquid metal jet X-ray source according to the present invention. [Figure 5] Figure 5 schematically shows a third embodiment of the liquid metal jet X-ray source according to the present invention. [Figure 6] Figure 6 schematically shows a fourth embodiment of the liquid metal jet X-ray source according to the present invention. 【0015】 In the drawings, corresponding features are indicated by the same reference number throughout. [Modes for carrying out the invention] 【0016】 Embodiments of the present invention provide characterization of an electron beam used for generating X-ray emission in a liquid metal jet X-ray source. To characterize the electron beam, the electron beam is scanned over an obscuring object, and the X-ray emission generated during such scanning is detected. The obscuring object can be an aperture, a liquid metal jet, or some reference object. 【0017】 From a general perspective, since the focal plane is typically where the electron beam interacts with the liquid metal jet target during operation to generate X-rays, it may be preferable to perform measurements at the focal plane of the electron beam. However, it is also conceivable to perform measurements on some other plane along the electron beam and mathematically transform the results so that they reflect the conditions at the focal plane. In some embodiments, such transformations may be established as part of a factory calibration procedure. 【0018】 In a preferred embodiment of the present invention, the characterization of the electron beam is performed using an object that obscures the path of the electron beam. When the electron beam is scanned in at least a portion of the interference region, the path of the electron beam is at least partially intersected by the obscuring object in some scanning directions, while the electron beam is not obscured in other scanning directions. Characteristics of the electron beam, such as the cross-sectional size or shape of the electron beam, can therefore be obtained based on the extent to which the electron beam is obscured in different scanning directions, which is then estimated by measuring the X-ray emission generated during the scanning of the electron beam. 【0019】 The occluding object may be positioned in various locations. For example, an aperture may be placed in front of the electron beam dump so that only electrons passing through the aperture are detected by the beam dump. This approach is useful in embodiments where the measured X-ray emission is generated by the interaction between the electron beam and the electron beam dump. Alternatively or additionally, the occluding object may be positioned within the interference region so as to intersect the electron beam at or near a location where it interacts with a liquid metal jet during the operation of the X-ray source. 【0020】 In some preferred embodiments, the liquid metal jet itself is used as the covering object, i.e., the edge over which the electron beam is scanned, and the X-ray emission to be measured may be the emission generated by the interaction between the electron beam and the liquid metal jet. 【0021】 In other embodiments, the reference object is inserted into the beampath of the electron beam when the measurement is performed and then removed before the normal operation of the X-ray source. Such a reference object can provide edges in two or more directions, thus facilitating, for example, the measurement of electron beam astigmatism. Measurements performed using a reference object are typically part of a factory calibration or maintenance procedure. 【0022】 For diagnostic purposes, similar measurements can also be made "on-site". Then, without calculating the actual characteristics of the electron beam, several quantities can be determined and compared with preset limit values. If the diagnostic measurements indicate that the electron beam is out of specification, the system can adjust the settings of the electron optical system until the measured quantities are within the limits, or alternatively, warn the operator that maintenance is required to achieve the system specifications. 【0023】 First, a general introduction will be given by referring to FIG. 2, which is a schematic perspective view of a liquid metal jet X-ray source 200 according to some embodiments of the present invention. The illustrated X-ray source 200 utilizes a liquid metal jet 210 as a target for an electron beam. Note that some of the illustrated features of the X-ray source 200 are only included as possible examples and may not necessarily be present or required for the operation of all embodiments. 【0024】 The X-ray source 200 includes electron sources 214, 246 and a liquid jet generator 208 configured to form a liquid jet 210 that functions as an electron target. The components of the X-ray source 200 are arranged within an airtight housing 242. However, some components such as a power supply 244 and a controller 247 can be arranged outside the airtight housing 242. It is also conceivable that various electron optical components operating by electromagnetic interaction can be arranged outside the housing 242 if the housing does not shield the electromagnetic field to a significant extent (e.g., austenitic stainless steel). 【0025】 The electron source generally includes a cathode 214 powered by a power supply 244 and an electron emitter 246, for example, a thermal ion, thermal field, or cold field charged particle source. Typically, the electron energy may range from about 5 keV to about 500 keV. The electron beam from the electron source is accelerated toward an accelerating aperture 248, where it enters an electron-optical system including an alignment plate 250, a lens 252, and a deflection plate 254. The variability of the alignment plate 250, lens 252, and deflection plate 254 can be controlled by signals provided by a controller 247. In the illustrated example, the deflection plate 250 and alignment plate 254 are operable to accelerate the electron beam in at least two transverse directions. After initial calibration, the alignment plate 250 is typically maintained at a constant setting throughout the entire working cycle of the X-ray source 200, while the deflection plate 254 is used to dynamically scan or adjust the electron spot position during use of the X-ray source 200. Controllable properties of the lens 252 include their respective focusing power (i.e., focal length). Figure 2 symbolically depicts the alignment, focusing, and deflection means in a manner that suggests they are electrostatic, but the present invention can be equally and fully embodied using electromagnetic devices or a mixture of electrostatic and electromagnetic-electro-optical components. The X-ray source 200 may also include a stigmeter coil 253 that can provide adjustment of the cross-sectional shape of the electron spot. 【0026】 Downstream of the electron-optical system, the exit electron beam I2 intersects with the liquid metal jet 210 in the interference region 212. This is where X-ray generation can occur. The X-ray emission may be directed out of the housing 242 in a direction not consistent with the electron beam propagation direction. Any portion of the electron beam I2 that continues to pass through the interference region 212 can reach the electron beam dump 228 which is electrically connected to ground. As shown in the figure, the electron beam dump 228 can be positioned at a distance D from the interference region 212 so as not to interfere with the normal operation of the X-ray source 200. An aperture (not shown in Figure 2) may be provided, which is positioned so that electrons passing through the aperture collide with the electron beam dump 228, while electrons not passing through the aperture do not. 【0027】 Figure 1 illustrates the method according to the present invention. 【0028】 A method according to the present invention for characterizing an electron beam in a liquid metal jet X-ray source includes the steps of: providing an electron beam and directing the electron beam into an interference region S110; providing an electron beam dump connected to a ground potential to receive the electron beam after it has traversed the interference region S120; scanning the electron beam over at least a portion of the interference region S130; measuring the X-ray emission generated during the scan to obtain an X-ray profile S140; and calculating electron beam characteristics based on the X-ray profile S150. 【0029】 In a preferred embodiment, step S140, which measures the X-ray emission generated during scanning, includes measuring the X-ray emission generated by the interaction between the electron beam and the electron beam dump. For example, the cross-sectional expansion (width) of the electron beam can be determined by scanning the electron beam across the interference region, thereby scanning across the electron beam dump, and simultaneously measuring the generated X-ray emission. An aperture may be provided such that the X-ray emission is generated only in the electron beam dump by any portion of the electron beam passing through the aperture. For example, an aperture can be provided as shown in Figure 3, in which case only electrons reaching the electron beam dump surface 124 contribute to the detected X-ray emission. By correlating the direction of the electron beam (e.g., with respect to the voltage applied to the corresponding deflection plate) with the detected X-ray emission, an X-ray profile can be obtained that can be used to calculate the cross-sectional expansion of the electron beam in the scanning direction. The total cross-sectional expansion of the electron beam can be calculated by scanning the electron beam in two or more directions across the aperture. 【0030】 Alternatively, rather than relying on an aperture that limits the amount of electrons reaching the electron beam dump, an object that partially intersects the path of the electron beam can be provided. Any object that absorbs and / or reflects electrons can be used. In this context, it may be preferable to use a liquid metal jet target for this purpose. The electron beam is then scanned across the interfering object, which acts as a kind of inverted aperture in the sense that it prevents electrons from reaching the electron beam dump. When the electron beam collides with the electron beam dump that is not obscured by the object, the maximum amount of X-ray emission is generated. As the electron beam is scanned over the object, the electron beam is partially obscured, and the amount of X-ray emission generated in the electron beam dump decreases until the electron beam is maximally obscured by the object. In this case as well, an X-ray profile is obtained that can be used to calculate the cross-sectional expansion of the electron beam. 【0031】 In other embodiments, the method involves measuring the X-ray emission generated by the interaction between the electron beam and a liquid metal jet target during the scanning of the electron beam. 【0032】 In a liquid metal jet X-ray source schematically shown in Figures 4 to 6, where one or more X-ray detectors are positioned to detect the X-ray emission generated by the interaction between the electron beam and the liquid metal jet, step S140, which measures the X-ray emission generated during scanning to obtain an X-ray profile, therefore includes measuring the X-ray emission generated by the interaction between the electron beam and the liquid metal jet. 【0033】 The effect of self-absorption of X-ray emission in a liquid metal jet target can be reduced by using two X-ray detectors 128a and 128b positioned on either side of the interference region, as schematically shown in Figure 5. Step S140, which measures the X-ray emission generated during the scan to obtain the X-ray profile, may include considering the sum of the X-ray emission detected by the two detectors, for example, by summing the outputs from the two detectors. If the two detectors are positioned symmetrically on either side of the interference region, the sum of the outputs compensates for any self-absorption-induced asymmetry in the X-ray profile, such that correspondingly higher or lower levels of X-ray emission are detected by the other detector and therefore recorded by one of the detectors. If the detectors are not positioned symmetrically, appropriate weights can be applied to each output before summing. 【0034】 The effect of self-absorption of X-ray emission in a liquid metal jet can be further reduced by measuring the X-ray emission generated from the same side as the electron beam impacting the liquid metal jet, as schematically shown in Figure 6. In such a setup, there is no self-absorption between the interference region and the X-ray detector that affects the generated X-ray emission. This may be particularly useful for alignment purposes, as the detector "verifies" where the electron beam impacts the liquid metal jet. The X-ray detector can be equipped with imaging capabilities, for example, by including a CCD array, and to improve imaging, a pinhole can be provided between the CCD array and the interference region where the electron beam impacts the liquid metal jet. 【0035】 For example, an X-ray detector including a CCD array and a pinhole similar to the one described above may also be useful in a setup like the one shown in Figure 4. The X-ray detector then "verifies" the X-ray emission being produced. 【0036】 Alternatively, some other object capable of generating X-ray emission during electron collisions may be placed in the interference region during characterization, in which case the liquid metal jet may not be present during characterization. 【0037】 Figure 3 schematically shows a liquid metal jet X-ray source 300 according to a first embodiment of the present invention. The X-ray source 300 comprises an electron source / cathode 110 that emits electrons toward an anode 114. An accelerating potential 112 can be applied between the cathode 110 and the anode 114 to accelerate the emitted electrons. Downstream of the anode 114, one or more alignment coils 116 are located for aligning the electron beam. One or more focusing lenses 118 and deflection plates 120 are also located along the electron beam path to focus and direct the electron beam toward an interference region where the electron beam can interact with the liquid metal jet target 122. During normal operation, useful X-ray emission is generated by the interaction between the electron beam and the liquid metal jet 122 in the interference region. The X-ray source 300 also comprises an electron beam dump 124 into which electrons that have passed through the interference region collide. The electron beam dump 124 is electrically grounded, and as a result, electrons that collide with it are discarded, i.e., dumped. 【0038】 In the embodiment shown in Figure 3, the electron beam dump 124 is positioned to generate X-ray emission when electrons collide with it. An X-ray detector 128 is provided to detect the X-ray emission generated from the electron beam dump 124. The detector 128 can be positioned to detect only the X-ray emission generated from the electron beam dump (and not, for example, the emission generated from the interaction between the electron beam and the liquid metal jet 122). In such a configuration, alignment and focusing procedures can be performed in a similar manner to conventional electron beam dumps where the current through the beam dump is measured, as described in WO2012 / 087238 above, for example. However, since the procedure uses the X-ray emission generated from the beam dump 124 rather than the current through the beam dump, it is not necessary to maintain the beam dump 124 at a specific potential. In contrast, in embodiments of the present invention, the electron beam dump 124 is electrically grounded, as shown in 126 of Figure 3. Therefore, for example, if a metal droplet adheres to the edge of the beam dump 124, no harmful short circuit occurs, and the deposited metal droplet also generates X-rays during electron collisions, thus not impairing functionality. 【0039】 In some embodiments, the design of the electron beam dump 124 can be optimized in the sense that the material of the electron beam dump 124 provides a similar cross-section for X-ray generation for all relevant orientations of the electron beam. One embodiment may include, for example, a flat surface positioned at an appropriate angle with respect to the direction of impact of the electron beam. In other embodiments, the electron beam dump 124 may include a cylindrical surface, the radius of which is large compared to the distance the electron beam traverses the surface during the electron beam scan across the aperture of the electron beam dump. 【0040】 Preferably, the electron beam dump is equipped with a suitable cooling arrangement to deal with the thermal load associated with electron beam collisions. 【0041】 In embodiments of the present invention, the electron beam dump 124 is electrically grounded. This effectively prevents charge accumulation in the beam dump 124 and avoids the prior art problems of short circuits between the beam dump and other parts of the arrangement. However, it should be noted that the electron beam dump 124 does not need to be consistently connected to earth. For example, when a threshold potential is reached in the beam dump, the ground may be intermittently activated to dump the accumulated charge to earth through an appropriate current-limiting arrangement, such as a resistor, at an optional choice. However, a preferred embodiment has an electron beam dump 124 that is consistently connected to electrical ground so that the electron beam dump is maintained at a ground potential. Within the scope of the present invention, it is conceivable to create a virtual ground potential for the housing and the electron beam dump, i.e., these components can be actively held at a specific potential that is not necessarily equal to zero. This type of embodiment may have design advantages in some situations, but the general concept of the present invention is not affected. 【0042】 Any suitable type of detector, such as a cadmium telluride (CdTe) diode in a tungsten (W) housing, can be used as the X-ray detector 128. 【0043】 In the embodiment shown in Figure 3, the X-ray profile during the electron beam scan is obtained by measuring the X-ray emission generated by the interaction between the electron beam and the electron beam dump 124. Optionally, an object such as a liquid metal jet target 122 may be present to partially obscure the electron beam during the scan. The X-ray detector 128 is configured to detect only the X-ray emission from the electron beam dump and not to detect the emission generated from the interaction between the electron beam and the liquid metal jet or any other part of the system, such as a housing or aperture placed between the interference region and the electron beam dump. 【0044】 Other embodiments may also rely on detecting X-ray emission generated by the interaction between the electron beam and the liquid metal jet of source 100, or between the electron beam and a reference object placed in the electron beam path. Figure 4 schematically shows an embodiment of an X-ray source 400 in which an X-ray detector 128 is positioned to detect X-rays generated in the interference region. The X-ray sensor for detecting X-rays generated in the interference region is preferably a second sensor dedicated to this purpose. The X-ray detector 128 is conveniently positioned outside the vacuum chamber of the X-ray source and can detect X-ray emission through an X-ray transmission window. A typical X-ray source according to the present invention may have one or more X-ray transmission windows or ports from which the generated X-ray emission is extracted. The detector 128 can be conveniently positioned in one such port. The detector 128 can thereby detect X-ray emission when the electron beam strikes a liquid metal target (or a appropriately positioned reference object), but does not detect X-ray emission when the electron beam does not strike a target. This allows for the acquisition of an X-ray intensity profile by sampling the X-ray detector 128 while the electron beam is scanning the target, which can then be used to estimate properties of the electron beam, such as its cross-sectional dimensions. Self-absorption in the target may result in a somewhat distorted profile measurement, but this can be compensated for by subtracting a fluctuating background or by using only X-ray emission at energies where self-absorption in the target is reduced, for example, by detecting only X-ray emission with energies well above the X-ray absorption limit of the target material. 【0045】 Figure 5 schematically shows another embodiment of the liquid metal jet X-ray source 500 according to the present invention, where self-absorption is compensated by using two X-ray detectors 128a and 128b positioned at different angles to the liquid metal jet 122. Thus, a compensated measurement can be obtained by considering the sum of the X-ray emissions detected by the two detectors. 【0046】 Figure 6 schematically illustrates yet another embodiment, in which the X-ray detector 128 is positioned below (or above) the electron beam, but within the line of sight from the interference region. As long as the X-ray detector has a sufficiently narrow field of view, any radiation generated from electrons colliding with the electron beam dump 124 can be prevented from being detected by the X-ray detector 128. Such positioning of the X-ray detector can reduce artifacts caused by self-absorption at the target. 【0047】 As can be understood, the detector arrangements shown in Figures 3 to 6 can also be combined. For example, an X-ray source and / or corresponding method involving the measurement of X-ray emission generated by the interaction between an electron beam and an electron beam dump, as shown in Figure 3, can be combined (i.e., complemented) with the measurement of X-ray emission generated by the interaction between an electron beam and a liquid metal jet or another occluding object, as shown in any of Figures 4 to 6. It is also conceivable that the X-ray emission generated by the interaction between the electron beam and the electron beam dump is not considered when determining the X-ray profile, and therefore has an implementation that relies only on one or more of the detection schemes described with reference to Figures 4 to 6. 【0048】 In various embodiments of the present invention, an X-ray profile is obtained by scanning the electron beam across a liquid metal jet, a reference object, an aperture, or similar, and the resulting X-ray profile can be used to calibrate or adjust the focus of the electron beam. A second sensor, such as a sensor that detects backscattered electrons, can be used to align the electron beam along the optical axis of the system. However, the use of such a backscatter sensor is not very advantageous for non-flat targets, as the backscatter coefficient changes as the electron beam scans across the target. 【0049】 In cases where a metal droplet accumulates somewhere between the target and the X-ray detector, a reduction in the amount of X-ray radiation reaching the detector may occur, but this does not impair functionality, and an X-ray intensity profile can still be obtained, albeit with a slightly reduced intensity, which can be used to determine the electron beam width. 【0050】 For example, in cases where an X-ray detector is used that has sufficient imaging capability by including a pinhole and / or a CCD array, the focal spread in a direction substantially parallel to the liquid metal jet can be obtained by scanning the electron beam along that direction while detecting the amount of radiation reaching the detector. The distance the electron beam spot must move for the X-ray signal to transition from full signal to zero, or any other well-defined limit, corresponds to the beam spot size. 【0051】 In the embodiments described above, detection of X-ray emission is direct (e.g., by using a diode-based detector). However, detection of X-ray emission may also be indirect, by first converting the X-ray emission into emission having a lower frequency, and then detecting the lower frequency emission (e.g., using a scintillator and a visible light detector). In all embodiments, it is preferable to shield or position the X-ray detector so that only radiation from the intended source is detected. As described above, such shielding can be achieved by a CdTe diode placed inside a W casing. In a preferred embodiment, the X-ray detector has a CdTe diode placed at an appropriate depth inside the W cylinder to shield from undesirable X-ray emission. Other types of collimators that limit the field of view of the X-ray detector are conceivable within the scope of the invention. 【0052】 In summary, embodiments of the present invention provide a method for determining properties of an electron beam, such as cross-sectional expansion. An electron beam is directed into an interference region. After passing through the interference region, the electron beam collides with an electron beam dump, and the charge is discharged to electrical ground. The electron beam is scanned over at least a portion of the interference region, and the X-ray emission generated during the scan is measured to obtain an X-ray profile relating the measured X-ray emission to the electron beam direction. Then, based on the generated X-ray profile, electron beam properties, such as cross-sectional expansion, are calculated. 【0053】 In some embodiments, X-ray emission is generated by the interaction between the electron beam and the beam dump, and the electron beam passes through an aperture before reaching the electron beam dump. Only the portion of the electron beam that passes through the aperture can reach the electron beam dump and thus contribute to the generation of X-ray emission. Therefore, the cross-sectional expansion of the electron beam can be calculated using the X-ray profile. It is also conceivable that the aperture is embodied as an extension of the electron beam dump itself. In other embodiments, the aperture is embodied as an opening in the wall of a liquid metal jet X-ray source, as schematically shown in the accompanying drawings. As is understood, in embodiments utilizing such an aperture, the electron beam needs to be scanned over a sufficiently large angle to reach the edge of the aperture. 【0054】 In other embodiments, an object is provided that partially intersects the path of the electron beam during scanning. Such an object can take many different forms, insofar as it has properties that absorb and / or reflect electrons so that fewer electrons reach the electron beam dump when the object partially intersects the path of the electron beam. The object intersecting the path may be a liquid metal jet present in the interference region. 【0055】 While several exemplary embodiments have been described herein, those skilled in the art will not be limited to these examples when implementing embodiments of the present invention. Rather, many modifications and variations are possible within the scope of the appended claims. In particular, X-ray sources comprising two or more targets or two or more electron beams can be considered to be within the scope of the concept of the present invention. Furthermore, the types of X-ray sources described herein can be advantageously combined with X-ray optics and / or detectors tailored to specific applications, exemplified by, but not limited to, medical diagnostics, non-destructive testing, lithography, crystal analysis, microscopy, materials science, surface physics, protein structure determination by X-ray diffraction, X-ray optical spectroscopy (XPS), limiting dimension small-angle X-ray scattering (CD-SAXS), and X-ray fluorescence. After reading and understanding this disclosure in relation to the appended drawings, those skilled in the art will be able to implement various embodiments. The following is a direct reproduction of the claims as originally filed. [1] A method for characterizing an electron beam in a liquid metal jet X-ray source, Providing the aforementioned electron beam and directing the aforementioned electron beam towards the interference region, To provide an electron beam dump connected to a ground potential for receiving the electron beam after the electron beam has traversed the interference region, Scanning the electron beam over at least a portion of the interference region, To obtain an X-ray profile, the X-ray emission generated by the interaction between the electron beam and the electron beam dump during the scan is measured, A method comprising calculating electron beam characteristics based on the aforementioned X-ray profile. [2] The method according to [1], further comprising providing an object that partially intersects the path of the electron beam during the scan, wherein the object absorbs and / or reflects electrons. [3] The method according to [2], wherein the object is a liquid metal jet present in the interference region. [4] The method according to [3], further comprising calculating the properties of the liquid metal jet based on the X-ray profile. [5] The method according to any one of [2] to [4], further comprising the step of measuring X-ray emission to obtain an X-ray profile, which includes measuring X-ray emission generated by the interaction between the electron beam and the object. [6] The method according to any one of [1] to [4], further comprising providing an aperture between the interference region and the electron beam dump, wherein the aperture is arranged such that only electrons passing through the aperture contribute to the X-ray emission measured during the scan. [7] The method according to [6], wherein scanning the electron beam across the interference region includes scanning the electron beam across the aperture. [8] The method according to [5], further comprising providing a pinhole, measuring the profile of the X-ray emission generated during the scan, and detecting the X-ray emission that has passed through the pinhole. [9] A liquid metal jet X-ray source, An electron source that provides an electron beam and is positioned to direct the electron beam into an interference region, An electron beam dump connected to ground potential and positioned to receive the electron beam after it has traversed the interference region, A scanning device capable of scanning the electron beam over at least a portion of the interference region, An X-ray sensor positioned and arranged to detect X-ray emission generated by the interaction between the electron beam and the electron beam dump, A liquid metal jet X-ray source comprising a scanning device and a circuit operably connected to the X-ray sensor, wherein the circuit is configured to determine an X-ray profile during scanning of the electron beam.

[10] The liquid metal jet X-ray source according to [9], further configured to calculate the characteristics of the electron beam based on the X-ray profile.

[11] The liquid metal jet X-ray source according to [9] or

[10] further comprises a reference object detachably provided so as to partially intersect the path of the electron beam during the scan, wherein the reference object absorbs and / or reflects electrons.

[12] A liquid metal jet X-ray source according to any one of [9] to

[11] , further comprising a collimator that limits the field of view of the X-ray sensor.

[13] A liquid metal jet X-ray source according to any one of [9] to

[12] , further comprising an aperture between the interference region and the electron beam dump, wherein the aperture is arranged such that only electrons passing through the aperture contribute to the X-ray emission measured during the scan.

[14] The liquid metal jet X-ray source according to any one of [9] to

[13] further comprises a second X-ray sensor positioned and arranged to detect X-ray emission generated in the interference region.

[15] The liquid metal jet X-ray source according to

[14] further comprises a pinhole positioned and arranged such that the X-ray emission detected by the second X-ray sensor passes through the pinhole.

Claims

[Claim 1] A method for characterizing an electron beam in a liquid metal jet X-ray source, Providing the aforementioned electron beam and directing the aforementioned electron beam towards the interference region, To provide an electron beam dump directly connected to ground potential for receiving the electron beam after it has crossed the interference region, Scanning the electron beam over at least a portion of the interference region, To obtain an X-ray profile, the X-ray emission generated by the interaction between the electron beam and the electron beam dump during the scan is measured, A method comprising calculating electron beam characteristics based on the aforementioned X-ray profile. [Claim 2] The method according to claim 1, further comprising providing an object that partially intersects the path of the electron beam during the scan, wherein the object absorbs and / or reflects electrons. [Claim 3] The method according to claim 2, wherein the object is a liquid metal jet present in the interference region. [Claim 4] The method according to claim 3, further comprising calculating the properties of the liquid metal jet based on the X-ray profile. [Claim 5] The method according to any one of claims 2 to 4, wherein the step of measuring X-ray emission to obtain an X-ray profile further comprises measuring X-ray emission generated by the interaction between the electron beam and the object. [Claim 6] The method according to any one of claims 1 to 4, further comprising providing an aperture between the interference region and the electron beam dump, wherein the aperture is arranged such that only electrons passing through the aperture contribute to the X-ray emission measured during the scan. [Claim 7] The method according to claim 6, wherein scanning the electron beam across the interference region includes scanning the electron beam across the aperture. [Claim 8] The method of claim 5, further comprising providing a pinhole, and measuring the profile of the X-ray emission generated during the scan, comprising detecting the X-ray emission that has passed through the pinhole. [Claim 9] A liquid metal jet X-ray source, An electron source that provides an electron beam and is positioned to direct the electron beam into an interference region, An electron beam dump, which is directly connected to the ground potential and positioned to receive the electron beam after it has traversed the interference region, A scanning device capable of scanning the electron beam over at least a portion of the interference region, An X-ray sensor positioned and arranged to detect X-ray emission generated by the interaction between the electron beam and the electron beam dump, A liquid metal jet X-ray source comprising a scanning device and a circuit operably connected to the X-ray sensor, wherein the circuit is configured to determine an X-ray profile during scanning of the electron beam. [Claim 10] The liquid metal jet X-ray source according to claim 9, wherein the circuit is further configured to calculate the characteristics of the electron beam based on the X-ray profile. [Claim 11] The liquid metal jet X-ray source according to claim 9 or 10, further comprising a reference object detachably provided so as to partially intersect the path of the electron beam during the scan, wherein the reference object absorbs and / or reflects electrons. [Claim 12] The liquid metal jet X-ray source according to claim 9 or 10, further comprising a collimator that limits the field of view of the X-ray sensor. [Claim 13] The liquid metal jet X-ray source according to claim 9 or 10, further comprising an aperture between the interference region and the electron beam dump, wherein the aperture is arranged such that only electrons passing through the aperture contribute to the X-ray emission measured during the scan. [Claim 14] The liquid metal jet X-ray source according to claim 9 or 10, further comprising a second X-ray sensor positioned and arranged to detect X-ray emission generated in the interference region. [Claim 15] The liquid metal jet X-ray source according to claim 14, further comprising a pinhole positioned and arranged such that the X-ray emission detected by the second X-ray sensor passes through the pinhole.

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