A method for measuring a high-power electron beam spot

Abstract

A kind of high-power electron beam spot measurement method, comprising the following steps: Faraday cup moves along straight trajectory;Electron beam spot moves along circular trajectory intersecting with the straight trajectory for several rounds, and when electron beam spot meets Faraday cup in each round, the Faraday cup obtains the coordinates of several acquisition points and corresponding current signals;The beam spot characteristics of the electron beam spot are obtained based on the coordinates of each round acquisition point and corresponding current signals;The present application makes electron beam spot do circular motion, greatly shortens the moving distance and time of Faraday cup when collecting electron beam spot electron, improves the measurement efficiency, at the same time, Faraday cup only contacts electron beam spot when it rotates to straight trajectory each time, further reduces the time of Faraday cup exposed in electron beam spot, effectively avoids that Faraday cup is burnt out in the process of measurement, so that the measurement method can be applied to larger power electron beam spot.

Description

Technical Field

[0001] This invention relates to the field of electron beam measurement, and more specifically to a method for measuring the spot size of a high-power electron beam. Background Technology

[0002] Measuring the electron beam spot allows us to determine whether the electron beam generated by the electron gun meets the requirements for use. Currently, the main methods for measuring the electron beam spot include direct electron bombardment, CCD observation, and knife-edge blocking scanning. Direct bombardment qualitatively determines the size and uniformity of the beam spot based on the bombardment marks, but its measurement accuracy is poor and it can damage the sample surface. CCD observation acquires signals using a CCD detector and transmits them to a computer for imaging, but it has difficulties in directionally calculating the size and uniformity of the beam spot. Knife-edge blocking scanning generates interference signals, primarily secondary electrons, during use, which can introduce uncertainties into the accuracy of the measurement results.

[0003] To improve the accuracy of electron beam spot measurement, patent CN111308542A discloses a method for measuring electron gun beam spot performance. This method determines the scanning area based on the electron beam spot, and then controls a Faraday cup to move along the X-axis or Y-axis within the fixed scanning area. Each movement step of the Faraday cup collects the current signal at the corresponding position, thereby generating an electron beam spot distribution characteristic map. While this method can collect the energy distribution of the electron beam spot by moving the Faraday cup within the fixed scanning area, the movement trajectory of the Faraday cup is relatively long. To obtain a higher precision beam spot distribution, the Faraday cup needs to move for an even longer time within the scanning area. Furthermore, for high-power electron beam spots, such as those above 5kW, the surface of the Faraday cup exposed to the electron beam spot for extended periods will be burned, preventing normal collection of electrons. This means that traditional methods are only suitable for lower-power electron beams. Summary of the Invention

[0004] The purpose of this invention is to provide a method for measuring high-power electron beam spot. This method controls a Faraday cup to move linearly in the vertical direction while simultaneously controlling the electron beam spot to move in a circular motion. Each time the electron beam spot passes through the Faraday cup, the Faraday cup collects the current signal of the electron beam spot. The shape and energy distribution of the electron beam spot are then obtained by processing the current signal. This method not only significantly shortens the measurement time but also significantly reduces the time that the Faraday cup is exposed to the moving electron beam spot, thus making it suitable for measuring electron beam spots with higher power.

[0005] This invention is achieved through the following technical solution:

[0006] A method for measuring the spot size of a high-power electron beam includes the following steps:

[0007] The Faraday cup moves at a constant speed along a straight trajectory.

[0008] The electron beam spot moves periodically around a circular trajectory that intersects the straight line trajectory several times, and when the electron beam spot encounters the Faraday cup in each circle, the Faraday cup acquires the current signal of the electron beam spot.

[0009] The current signal is sampled to obtain the coordinates of several acquisition points and the corresponding voltage signals;

[0010] The beam spot characteristics of the electron beam are obtained based on the coordinates of each acquisition point and the corresponding voltage signal.

[0011] In the X-axis direction, the distance between two adjacent acquisition points is related to the sampling frequency and the moving speed of the electron beam spot; in the Y-axis direction, the distance between two adjacent acquisition points is related to the time it takes for the electron beam spot to move one revolution along the circular trajectory and the moving speed of the Faraday cup.

[0012] In this technical solution, the electron gun continuously emits electrons to form an electron beam. The electron beam is subjected to the transverse action of a periodic magnetic field, and ultimately makes periodic circular motion along a circular trajectory on a cross section perpendicular to the electron beam's motion. The Faraday cup, on the other hand, passes through the circular trajectory along a straight line. In some embodiments, the straight line trajectory can penetrate the circular trajectory, for example, extending from the outside of the circular trajectory to the inside of the circular trajectory, and then from the inside to the outside, i.e., the straight line trajectory and the circular trajectory intersect twice; in one or more embodiments, the straight line trajectory can also complete the measurement by intersecting the circular trajectory only once.

[0013] In this technical solution, once the electron beam spot reaches the required power, the Faraday cup is controlled to move along a straight trajectory. When the Faraday cup moves to a circular trajectory, it encounters the circularly moving electron beam spot. Each time the electron beam spot rotates once, the Faraday cup at different positions on the straight trajectory encounters the electron beam spot once, until the Faraday cup moves out of the circular trajectory. In one or more embodiments, the Faraday cup can move vertically, horizontally, or preferably along any diameter of the circular trajectory. In some embodiments, the straight trajectory can also be collinear with a chord of the circular trajectory, but the greater the distance between the chord and the diameter, the more distorted the energy distribution of the collected electron beam spot will be. In this technical solution, the Y-axis is collinear with the straight trajectory; the Y-axis direction refers to several straight lines parallel to the Y-axis; the X-axis direction refers to several straight lines perpendicular to the Y-axis.

[0014] When the Faraday cup encounters the electron beam spot, it collects electrons from the beam, generating voltage signals at multiple sampling points. Any existing Faraday cup can be used. In some preferred embodiments, the Faraday cup described in patent CN111722263B filed by the inventors can be used to improve its cooling effect and make it suitable for higher power beam spot measurements.

[0015] In this technical solution, the Faraday cup collects a current signal every time the electron beam spot rotates once and encounters it. Sampling the current signal yields the coordinates of several collection points and the corresponding voltage signals. The number of collection points is related to the sampling frequency and the scanning frequency of the electron beam spot. Therefore, by controlling the sampling frequency and / or the electron beam scanning frequency, the number of collection points per revolution of the electron beam spot can be adjusted, thereby adjusting the measurement accuracy.

[0016] The coordinates of the acquisition points include a first coordinate and a second coordinate. For example, the first coordinate can be either the x-coordinate or the y-coordinate, and the second coordinate can be either the y-coordinate or the x-coordinate. Taking the first coordinate as the x-coordinate and the second coordinate as the y-coordinate as an example, assuming the electron beam spot rotates one revolution, the number of acquisition points is N. x If the distance between two adjacent acquisition points along the X-axis is Δx, then the acquisition points generated by the electron beam spot rotating for the first time are (0, 0), (Δx, 0), (2Δx, 0), ..., (N x -1)Δx, 0); and the distance between two adjacent acquisition points in the Y-axis direction is Δy, then the acquisition points generated by the second rotation of the electron beam spot are (0, Δy), (Δx, Δy), (2Δx, Δy), ..., ((N x -1)Δx, Δy); and so on, the sampling points generated by the Mth rotation of the electron beam spot are (0, (M-1)Δy), (Δx, (M-1)Δy), (2Δx, (M-1)Δy), ..., (N x -1)Δx, (M-1)Δy). By unfolding the coordinates of the acquisition points, a two-dimensional plane can be obtained. After mapping the current signals at each acquisition point to the two-dimensional plane, the energy distribution and shape of the electron beam spot can be obtained. The total number of acquisition points on the two-dimensional plane is the product of the number of rotations and the number of acquisition points per rotation.

[0017] In this technical solution, the distance Δx between two adjacent acquisition points in the X-axis direction is related not only to the sampling frequency but also to the moving speed of the electron beam spot; the distance Δy between two adjacent acquisition points in the Y-axis direction mainly depends on the time it takes for the electron beam spot to rotate one revolution and the moving speed of the Faraday cup.

[0018] In this technical solution, by making the electron beam spot move in a circular motion, the moving distance and time of the Faraday cup when collecting electrons from the electron beam spot are greatly shortened, thus improving the measurement efficiency. At the same time, the Faraday cup only comes into contact with the electron beam spot each time it rotates to a straight trajectory, further reducing the time the Faraday cup is exposed to the electron beam spot and effectively preventing the Faraday cup from being burned out during the measurement process. This allows the measurement method to be applied to electron beam spots with higher power.

[0019] Furthermore, the formula for calculating the distance Δx between two adjacent sampling points along the X-axis is:

[0020]

[0021] Among them, f c V is the sampling frequency. e The velocity of the electron beam spot.

[0022] In this technical solution, the value of the spacing Δx is related to the sampling frequency f. c and the movement velocity V of the electron beam spot e Related. The sampling frequency refers to the sampling frequency of the data acquisition card of the acquisition unit connected to the Faraday cup. In one or more embodiments, the required sampling frequency can be calculated based on the value of the distance Δx between the two required acquisition points in the X-axis direction, or the value of the distance Δx between two adjacent acquisition points in the X-axis direction can be calculated based on the set sampling frequency.

[0023] Furthermore, the moving speed V of the electron beam spot e The calculation formula is:

[0024] V e =l·f e

[0025] l = 2π·r

[0026] Where l is the circumference of the circular trajectory, r is the radius of the circular trajectory, and f e The scanning frequency of the electron beam spot.

[0027] In this technical solution, the scanning frequency of the electron beam spot can be set by adjusting the electron gun. The radius of the circular trajectory can be measured in advance, for example, by controlling the electron gun to scan along a circular trajectory on the collecting electrode, and calculating the radius of the circular trajectory from the trace formed on the collecting electrode.

[0028] Furthermore, the electron beam spot moves one full circle along the circular trajectory, and the number of acquisition points obtained is...

[0029]

[0030] Further, the radius r of the circular trajectory is at least 5 times the beam spot diameter D. Preferably, the radius r of the circular trajectory is at least 8 times the beam spot diameter D, and more preferably, the radius r of the circular trajectory is at least 10 times the beam spot diameter D.

[0031] Furthermore, the formula for calculating the distance Δy between two adjacent sampling points along the Y-axis is:

[0032] Δy=V y ·Δt

[0033] Among them, V y Let Δt be the speed at which the Faraday cup moves, and let Δt be the time it takes for the electron beam spot to complete one revolution along the circular trajectory.

[0034] In this technical solution, the Faraday cup can be driven to move along a straight line by a displacement stage, and the moving speed V of the Faraday cup can be set. y The time Δt for the electron beam spot to move one revolution can be calculated using the formula... We obtain f, where f e The scanning frequency of the electron beam spot.

[0035] Furthermore, the diameters of the straight line trajectory and the circular trajectory are collinear.

[0036] Furthermore, the electron beam spot moves along the straight line trajectory from the inside to the outside of the circular trajectory, or vice versa. In this technical solution, the straight line trajectory and the circular trajectory intersect only once, which can further shorten the measurement time.

[0037] In some preferred embodiments, the Faraday cup is connected to a data acquisition card in the acquisition unit. The data acquisition card can convert the current signal of the Faraday cup into a voltage signal for sampling, and transmit the sampled voltage signal to the computer of the acquisition unit. The data is then processed using a data processing program, such as LabVIEW, to visualize the shape of the electron beam and the beam spot energy distribution map and other electron beam spot characteristics in a two-dimensional plane or three-dimensional space.

[0038] Further, the diameter of the electron beam spot is 10 to 30 times the diameter of the collecting port of the Faraday cup. In some preferred embodiments, the diameter of the electron beam spot is 8 to 12 mm, and the diameter of the collecting port of the Faraday cup is 0.4 to 0.8 mm.

[0039] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0040] This invention significantly shortens the movement distance and time of the Faraday cup when collecting electrons from the electron beam spot by making the electron beam spot rotate in a circular motion, thereby improving measurement efficiency. At the same time, the Faraday cup only comes into contact with the electron beam spot each time it rotates to a straight trajectory, further reducing the time the Faraday cup is exposed to the electron beam spot and effectively preventing the Faraday cup from being burned out during the measurement process. This allows the measurement method to be applied to electron beam spots with higher power. Attached Figure Description

[0041] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0042] Figure 1 This is a flowchart of the electron beam spot measurement method in a specific embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the electron beam spot measurement device in a specific embodiment of the present invention;

[0044] Figure 3 The illustration shows the vertical movement distance Δy of the Faraday cup in a specific embodiment of the present invention, the rotation of the electron beam spot around the Faraday cup and its intersection with the Faraday cup, the data collection at a certain sampling rate, and the distance Δx between two adjacent sampling points.

[0045] Figure 4 This diagram illustrates the position of the electron beam spot at multiple moments during one rotation of the electron beam spot in a specific embodiment of the present invention.

[0046] Figure 5 This is a diagram showing the energy distribution of the electron beam spot in the XY two-dimensional plane in a specific embodiment of the present invention;

[0047] Figure 6 This is an energy distribution diagram of the electron beam spot in three-dimensional space in a specific embodiment of the present invention.

[0048] The attached diagram shows the markings and corresponding component names:

[0049] 1-Electron gun, 2-Electron beam spot, 3-Faraday cup, 4-Displacement stage, 5-Collector, 6-Collection unit, 7-Vacuum pumping unit, 8-Collection port of Faraday cup. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0051] In the description of this invention, it should be understood that the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0052] Example 1:

[0053] like Figure 1 The method for measuring the spot size of a high-power electron beam, as shown, includes the following steps:

[0054] The Faraday cup moves at a constant speed along a straight trajectory.

[0055] The electron beam spot moves periodically around a circular trajectory that intersects the straight line trajectory several times, and when the electron beam spot encounters the Faraday cup in each circle, the Faraday cup acquires the current signal of the electron beam spot.

[0056] The current signal is sampled to obtain the coordinates of several acquisition points and the corresponding voltage signals;

[0057] The beam spot characteristics of the electron beam are obtained based on the coordinates of each acquisition point and the corresponding voltage signal.

[0058] In the X-axis direction, the distance between two adjacent acquisition points is related to the sampling frequency and the moving speed of the electron beam spot; in the Y-axis direction, the distance between two adjacent acquisition points is related to the time it takes for the electron beam spot to move one revolution along the circular trajectory and the moving speed of the Faraday cup.

[0059] In this embodiment, the order in which the Faraday cup moves along a straight line and the electron beam spot moves along a circular trajectory is not limited.

[0060] like Figure 3 As shown, assuming the electron beam spot rotates one revolution, the number of sampling points is N. x If the distance between two adjacent acquisition points along the X-axis is Δx, then the acquisition points generated by the electron beam spot rotating for the first time are (0, 0), (Δx, 0), (2Δx, 0), ..., (N x -1)Δx, 0); and the distance between two adjacent acquisition points in the Y-axis direction is Δy, then the acquisition points generated by the second rotation of the electron beam spot are (0, Δy), (Δx, Δy), (2Δx, Δy), ..., ((N x-1)Δx, Δy); and so on, the sampling points generated by the Mth rotation of the electron beam spot are (0, (M-1)Δy), (Δx, (M-1)Δy), (2Δx, (M-1)Δy), ..., (N x -1)Δx, (M-1)Δy). By unfolding the coordinates of the acquisition points, a two-dimensional plane can be obtained. After mapping the current signals at each acquisition point to the two-dimensional plane, the energy distribution and shape of the electron beam spot can be obtained. The total number of acquisition points on the two-dimensional plane is the product of the number of rotations and the number of acquisition points per rotation. In some embodiments, the data values ​​are assigned to three-dimensional coordinates.

[0061] In some embodiments, the straight line trajectory can pass through the circular trajectory, for example, extending from the outside of the circular trajectory to the inside of the circular trajectory, and then from the inside to the outside, that is, the straight line trajectory and the circular trajectory intersect twice; in one or more embodiments, the straight line trajectory can also complete the measurement by intersecting the circular trajectory only once.

[0062] In one or more embodiments, the Faraday cup can move vertically, horizontally, or preferably along any diameter of a circular trajectory.

[0063] In some preferred embodiments, the Faraday cup may be the Faraday cup in patent CN111722263B applied for by the inventors' team, in order to improve the cooling effect of the Faraday cup and make it suitable for higher power beam spot measurement.

[0064] In this embodiment, by making the electron beam spot move in a circular motion, the moving distance and time of the Faraday cup when collecting electrons from the electron beam spot are greatly shortened, improving the measurement efficiency. At the same time, the Faraday cup only comes into contact with the electron beam spot each time it rotates to a straight trajectory, further reducing the time the Faraday cup is exposed to the electron beam spot, effectively preventing the Faraday cup from being burned out during the measurement process, and enabling this measurement method to be applied to electron beam spots with higher power.

[0065] In some preferred embodiments, the diameter of the straight line trajectory is collinear with that of the circular trajectory.

[0066] In some preferred embodiments, the electron beam spot moves along the straight-line trajectory from the inside to the outside of the circular trajectory, or vice versa. The straight-line trajectory intersects the circular trajectory only once, further reducing measurement time.

[0067] In some preferred embodiments, the current signal collected by the Faraday cup is sampled after being converted into a voltage signal.

[0068] In some preferred embodiments, the diameter of the electron beam spot is 10 to 30 times the diameter of the Faraday cup's collecting opening. In some preferred embodiments, the diameter of the electron beam spot is 8 to 12 mm, and the diameter of the Faraday cup's collecting opening is 0.4 to 0.8 mm. In some embodiments, the radius of the circular trajectory is preferably 80 to 120 mm.

[0069] Example 2:

[0070] Based on Example 1, such as Figure 2 As shown, electron gun 1 emits an electron beam spot 2 that scans along a circular trajectory at a specific frequency. When the required power is reached, the control displacement stage 4 moves the Faraday cup 3 downwards in the vertical direction, and the straight path of the Faraday cup 3 is collinear with the diameter of the circular trajectory of the electron beam spot 2. During the movement of the Faraday cup 3, for each rotation of the electron beam spot 2, the acquisition unit 6 samples the current signal acquired by the Faraday cup 3 to obtain N. x After rotating M times from each sampling point, a total of M*N samples are obtained. x Each sampling point and its corresponding voltage signal are collected. Subsequently, the sampled voltage signal can be displayed as a color change on a two-dimensional plane, or as a Z-axis value in three-dimensional space.

[0071] In one or more embodiments, the displacement stage 4 can be moved vertically and its speed, i.e., the speed of the Faraday cup 3, can be controlled via a LabVIEW program; the sampling frequency f of the data acquisition card can also be set via LabVIEW. c .

[0072] In one or more embodiments, the vacuum pumping unit 7 can be activated to evacuate the measurement environment before the measurement begins.

[0073] Example 3:

[0074] Based on the above embodiments, such as Figure 2 As shown, the formula for calculating the distance Δx between two adjacent sampling points along the X-axis is:

[0075]

[0076] Among them, f c V is the sampling frequency. e The velocity of the electron beam spot.

[0077] The formula for calculating the distance Δy between two adjacent second coordinates is:

[0078] Δy=V y ·Δt

[0079] Among them, Vy Let Δt be the speed at which the Faraday cup moves, and let Δt be the time it takes for the electron beam spot to complete one revolution along the circular trajectory.

[0080] In some embodiments, such as Figure 4 As shown, the moving speed V of the electron beam spot e The calculation formula is:

[0081] V e =l·f e

[0082] l = 2π·r

[0083] Where l is the circumference of the circular trajectory, r is the radius of the circular trajectory, and fe is the scanning frequency of the electron beam spot.

[0084] In one or more embodiments, the radius of the circular trajectory can be pre-measured, for example, by controlling the electron gun to scan along a circular trajectory on the collector electrode, and calculating the radius of the circular trajectory from the traces formed on the collector electrode.

[0085] In some preferred embodiments, the electron beam spot moves one full circle along the circular trajectory, and the number of acquisition points obtained is:

[0086]

[0087] Example 4:

[0088] In this embodiment, the radius r of the circular trajectory is 50 mm, the diameter D of the beam spot is 10 mm, the scanning frequency of the electron beam spot is 100 Hz, and the sampling frequency f is... c The Faraday cup moves at a speed of 1 Ms / s. y It is 10 mm / s.

[0089] like Figure 5 As shown, a total of 36 acquisition points were obtained. Based on the voltage values ​​at each acquisition point, the shape of the electron beam spot and the energy distribution of the spot on the two-dimensional plane were obtained. Figure 6 As shown, when the voltage value is taken as the Z-axis, the shape of the electron beam spot and the energy distribution of the spot in three-dimensional space are obtained.

[0090] The terms "first," "second," etc., used in this invention (e.g., first coordinate, second coordinate, etc.) are merely for clarity of description and are not intended to limit any order or emphasize importance. Furthermore, the term "connection" used in this invention, unless otherwise specified, can refer to a direct connection or an indirect connection via other components.

[0091] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for measuring the spot size of a high-power electron beam, characterized in that, Includes the following steps: The Faraday cup moves at a constant speed along a straight trajectory. The electron beam spot moves periodically around a circular trajectory that intersects the straight line trajectory several times, and when the electron beam spot encounters the Faraday cup in each circle, the Faraday cup acquires the current signal of the electron beam spot. The current signal is sampled to obtain the coordinates of several acquisition points and the corresponding voltage signals; The beam spot characteristics of the electron beam are obtained based on the coordinates of each acquisition point and the corresponding voltage signal. In the X-axis direction, the distance between two adjacent acquisition points is related to the sampling frequency and the moving speed of the electron beam spot; in the Y-axis direction, the distance between two adjacent acquisition points is related to the time it takes for the electron beam spot to move one revolution along the circular trajectory and the moving speed of the Faraday cup.

2. The method for measuring high-power electron beam spot according to claim 1, characterized in that, The formula for calculating the distance Δx between two adjacent data collection points along the X-axis is: Among them, f c V is the sampling frequency. e The velocity of the electron beam spot.

3. The method for measuring high-power electron beam spot according to claim 2, characterized in that, The electron beam spot's moving speed V e The calculation formula is: V e =l·f e l＝2π·r Where l is the circumference of the circular trajectory, r is the radius of the circular trajectory, and f e The scanning frequency of the electron beam spot.

4. The method for measuring high-power electron beam spot according to claim 3, characterized in that, The electron beam spot moves along the circular trajectory for one revolution, and the number of acquisition points obtained is:

5. The method for measuring high-power electron beam spot according to claim 3, characterized in that, The radius r of the circular trajectory is at least 5 times the beam spot diameter D.

6. The method for measuring high-power electron beam spot according to claim 1, characterized in that, The formula for calculating the distance Δy between two adjacent data collection points along the Y-axis is: Δy = V y ·Δt Among them, V y Let Δt be the speed at which the Faraday cup moves, and let Δt be the time it takes for the electron beam spot to complete one revolution along the circular trajectory.

7. A method for measuring high-power electron beam spot according to any one of claims 1 to 6, characterized in that, The diameters of the straight line trajectory and the circular trajectory are collinear.

8. The method for measuring high-power electron beam spot according to claim 7, characterized in that, The electron beam spot moves along the straight line trajectory from the inside of the circular trajectory to the outside of the circular trajectory, or the electron beam spot moves along the straight line trajectory from the outside of the circular trajectory to the inside of the circular trajectory.

9. The method for measuring high-power electron beam spot according to claim 7, characterized in that, The diameter of the electron beam spot is 10 to 30 times the diameter of the collection port of the Faraday cup.

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