A beam four-dimensional emittance measuring instrument based on orthogonal slits and a measurement method thereof

Abstract

The present invention discloses a beam four-dimensional emittance measuring instrument and measurement method based on orthogonal slits. A charged particle beam is incident on a slit assembly from the side of a first slit plate away from a second slit plate. After passing through the first slit, the charged particle beam forms a first beam group that is transmitted to the second slit plate. After passing through the second slit, the first beam group forms a second beam group that is transmitted to a fluorescence collection assembly. The fluorescence collection assembly includes a fluorescent screen and an image acquisition module. The fluorescent screen is used to receive the second beam group and generate fluorescence. The image acquisition module is used to collect the fluorescence pattern emitted by the second beam group bombarding the fluorescent screen. The data processing assembly is used to calculate the phase space distribution of the beam based on the fluorescence image and measure the emittance of the charged particle beam based on the phase space distribution. The beam four-dimensional emittance measuring instrument provided by the present invention can obtain a more complete four-dimensional phase space distribution by dividing the beam through slits in orthogonal directions, thereby increasing the completeness and accuracy of beam emittance measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of particle accelerator beam measurement, in particular to a beam four-dimensional emittance measuring instrument based on orthogonal slits and a measuring method. Background Art

[0002] High-brightness photocathode microwave electron guns are one of the most critical components for driving advanced synchrotron radiation sources and free-electron lasers. To achieve saturated emission in future high-gain free-electron lasers, the electron beams produced by these guns are generally required to possess characteristics such as a charge of 100 picocells and a normalized emittance below 0.2 mm / mrad. Beam emittance refers to the area of ​​the beam's phase space, defined by the particle position x and momentum px. Emittance is proportional to beam size and beam angle, and is typically measured in mm / mrad. In practice, emittance can also be calculated using the phase space defined by the position x and divergence angle x'. Based on a given phase space distribution, emittance can be calculated using statistical methods. The calculated emittance is the root mean square (RMS) emittance.

[0003] In order to accurately evaluate the performance and beam quality of a photocathode microwave electron gun, a special beam diagnostic device must be used to accurately characterize the spatial distribution and emittance of the beam phase. The beam energy at the exit of a photocathode microwave electron gun is usually in the order of mega-electronvolts (MeV). Due to the small lateral emittance, the beam is in a space-charge-dominated state, and emittance measurement methods based on linear optics generally have large measurement errors. Therefore, controlling the measurement error introduced by the space charge effect is crucial for the accurate measurement of extremely small emittances. At the same time, the measurement accuracy is also affected by the emittance fitting algorithm. Considering the limited signal-to-noise ratio range of the experimental data, image noise subtraction and weak signal pattern recognition cannot be fully achieved. Therefore, it is necessary to use the percentage emittance calculated by using information containing only a certain percentage of particles in the center of the bunch (100% full emittance and the commonly used 95% emittance).

[0004] Traditional methods for measuring the emittance of beams generated by photocathode microwave electron guns include single-slit scanning, multi-slit, pepper pot, and TEM grid methods. While single-slit scanning and multi-slit methods can only achieve two-dimensional beam phase space distribution and emittance measurements, the pepper pot and TEM grid methods enable four-dimensional phase space measurements. These methods utilize a regularly arranged micro-hole grid array to divide the beam into several sub-bunches. These sub-bunches have low charge and are in an emittance-dominated state, thereby keeping the emittance increase introduced by space charge effects within an acceptable range (generally less than 10%).

[0005] However, the spacing between adjacent microapertures in the microaperture array used in the pepper pot method must be large enough to prevent beamlets from overlapping at the downstream imaging module. Generally speaking, the spacing between adjacent microapertures should be several times the microaperture size. Therefore, the pepper pot method cannot obtain a complete beam phase space distribution, affecting the accuracy of emittance measurements. Summary of the Invention

[0006] The present invention provides a beam four-dimensional emittance measuring instrument and measurement method based on orthogonal slits. By continuously using slits in different directions to sequentially divide the charged particle beam emitted by an electron gun, only the particles passing through the orthogonal double slits bombard the fluorescent screen each time. The integral processing can obtain a relatively complete beam phase space distribution, and the emittance of the charged particle beam is calculated and measured based on the phase space distribution.

[0007] According to a first aspect of the present invention, there is provided a beam four-dimensional emittance measuring instrument based on an orthogonal slit, comprising a slit component, a fluorescence collection component and a data processing component;

[0008] The slit assembly includes a first slit plate and a second slit plate stacked along a first direction, the first slit plate including a first slit; the second slit plate including a second slit, the first slit extending along a second direction, and the second slit extending along a third direction, the first direction, the second direction, and the third direction being perpendicular to each other, and the first direction being perpendicular to the plane on which the first slit plate is located;

[0009] A charged particle beam is incident on the slit assembly from the side of the first slit plate away from the second slit plate. The charged particle beam is transmitted through the first slit to form a first beam group that is transmitted to the second slit plate. The first beam group is transmitted through the second slit to form a second beam group that is transmitted to the fluorescence collection assembly.

[0010] The fluorescence collection component is electrically connected to the data processing component. The fluorescence collection component includes a fluorescent screen and an image collection module. The fluorescent screen is used to receive the second beam group and generate fluorescence. The image collection module is used to collect the fluorescence pattern emitted by the second beam group bombarding the fluorescent screen. The data processing component is used to calculate the phase space distribution of the beam based on the fluorescence image and measure the emittance of the charged particle beam based on the phase space distribution.

[0011] Optionally, the size of the second beam group is greater than the width of the first slit.

[0012] Optionally, the width of the first slit and the second slit is greater than or equal to 10 microns.

[0013] Optionally, it also includes a drive component,

[0014] The driving assembly includes a first driving motor and a second driving motor; the first driving motor and the second driving motor are mechanically connected to the first slit plate and the second slit plate respectively;

[0015] The first driving motor is used to control the first slit plate to move in a stepwise manner along the third direction, and the second driving motor is used to control the second slit plate to move in a stepwise manner along the second direction.

[0016] Optionally, the signal-to-noise ratio of the second beam group on the fluorescent screen is greater than or equal to 3.

[0017] Optionally, the thicknesses of the first slit plate and the second slit plate further satisfy the requirement that the acceptance of the first slit is greater than the root mean square divergence angle of the second beam group.

[0018] Optionally, the axis direction of the charged particle beam is perpendicular to the plane where the fluorescent screen is located.

[0019] Optionally, the fluorescence collection component further includes a filter;

[0020] The visible fluorescent signal excited by the second beam after passing through the fluorescent screen passes through the filter and is incident on the image acquisition module.

[0021] Optionally, the fluorescence collection assembly further includes a reflector in a vacuum;

[0022] The angle between the reflector and the first direction is 45°.

[0023] According to a second aspect of the present invention, a method for measuring beam four-dimensional emittance based on orthogonal slits is provided, wherein the beam four-dimensional emittance measurement instrument based on orthogonal slits as described in any one of the first aspects of the present invention is used to measure the beam four-dimensional emittance, and the measurement method comprises:

[0024] Control the first slit plate to move along the third direction with a first step length d x Move to the first initial position; control the second slit plate to move along the second direction with a second step length d y moving to a second initial position;

[0025] controlling the charged particle beam to be emitted to the fluorescent screen through the first slit plate and the second slit plate;

[0026] Acquire the projection distribution of the second beam group carried on the fluorescent screen in the third direction and the second direction;

[0027] determining a divergence angle distribution of the charged particle beam according to a projection distribution of the second beam group in the second direction and the third direction;

[0028] controlling the second slit plate to perform multiple continuous step-wise scans along the second direction to calculate the phase space distribution of the charged particle beam;

[0029] controlling the first slit plate to perform a plurality of continuous step-wise scans along the third direction to calculate a phase space distribution of the charged particle beam;

[0030] determining the root mean square emittance of the charged particle beam using an adaptive ellipse elimination method according to the phase space distribution of the charged particle beam;

[0031] The emittance of the charged particle beam is calculated according to the root mean square emittance.

[0032] The present invention discloses a beam emittance measuring instrument, comprising a slit assembly, a fluorescence collection assembly and a data processing assembly; the slit assembly comprises a first slit plate and a second slit plate stacked along a first direction, the first slit plate comprising a first slit; the second slit plate comprising a second slit, the first slit extending along a second direction, the second slit extending along a third direction, the first direction, the second direction and the third direction being perpendicular to each other, and the first direction being perpendicular to the plane where the first slit plate is located; a charged particle beam is incident on the slit assembly from a side of the first slit plate away from the second slit plate, the charged particle beam is transmitted through the first slit to form a first beam group that passes through the second slit, and the first beam group is transmitted through the second slit to form a second beam group that passes through the fluorescence collection assembly; the fluorescence collection assembly and the data processing assembly are electrically connected, the fluorescence collection assembly comprising a fluorescent screen and an image collection module, the fluorescent screen being used to receive the second beam group and generate fluorescence, the image collection module being used to collect a fluorescence pattern emitted when the second beam group bombards the fluorescent screen, and the data processing assembly being used to calculate a phase space distribution of the beam based on the fluorescence image, and to measure the emittance of the charged particle beam based on the phase space distribution. The present invention provides a beam four-dimensional emittance measuring instrument and measurement method based on orthogonal slits. By continuously using slits in different directions to sequentially divide the charged particle beam emitted by an electron gun, only the particles passing through the orthogonal double slits bombard the fluorescent screen each time. The integral processing can obtain a relatively complete beam phase space distribution, and the emittance of the charged particle beam is calculated and measured based on the phase space distribution.

[0033] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 This is a diagram showing the working principle of measuring the emittance of a beam using the pepper pot method;

[0036] Figure 2 This is a partial schematic diagram of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention;

[0037] Figure 3 Schematic diagram of a slit assembly in a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention;

[0038] Figure 4 1 is a schematic structural diagram of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention;

[0039] Figure 5 This is a flow chart of a method for measuring four-dimensional emittance of a beam based on orthogonal slits provided by an embodiment of the present invention;

[0040] Figure 6 This is a diagram of beam error results of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0043] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. This is not limited herein.

[0044] Figure 1 This is a diagram showing the principle of measuring the emittance of a beam using the pepper pot method. Figure 1 A high-brightness photocathode microwave electron gun is an electron beam emitting device that uses a photocathode to generate a high-brightness electron beam under the irradiation of an intense laser pulse. In the prior art, there are various methods for measuring electron beam emittance, such as the pepper pot method. The pepper pot method is based on the principle of splitting the beam in a transverse two-dimensional plane (x, y), which can achieve four-dimensional emittance measurement of a single beam, such as Figure 1 As shown, a beam bunch emitted by a high-brightness photocathode microwave electron gun passes through a pepper hole baffle S1 at a distance L before impacting a fluorescent screen S2. The beam's direction is perpendicular to the screen S2. The pepper holes used are evenly distributed on the pepper hole baffle S1, arranged in a preset lattice pattern. This ensures that beams passing through adjacent holes do not overlap. After passing through the small hole array, the beam impacts the fluorescent screen S2. An optical imaging system can then be used to measure the relative distribution of the beams.

[0045] Each hole position (x i ,y i ) corresponding to the beam divergence angle distribution ρ(x i ,x i ',y i ,y i '), beam divergence angle distribution ρ(x i ,x i ',y i ,y iThe measurement principle and steps of the ') are as follows: At position S1, the charged particle beam passes through the baffle S1 with m×n pepper holes and is divided into m×n sub-bunches. The divergence angle distribution of the (i, j)th sub-bunch at position S1 is ρ(Δx i , Δy j ), where Δx i and Δy j is the deviation of the (i, j)th pepper hole in the horizontal and vertical directions relative to the beam reference track; after the beamlet is transmitted in the free space for a distance L, it reaches the position S2, and the x-direction projection distribution δ(Δx i ,Δy j ); According to the linear beam propagation theory, the beam transverse divergence angle distribution at the slit position is inferred, and the transformation relationship is: ρ(Δx i , Δy j )=δ(Δx i , Δy j ) / L, and obtain the lateral divergence angle distribution ρ(Δx i , Δy j ), i = 1, 2, 3, ..., m, j = 1, 2, 3, ..., n, the four-dimensional phase space distribution I (x i , x i ',y i ,y i It's worth noting that only a fraction of particles can pass through the pepper aperture, so the resulting phase space distribution is incomplete. Offline analysis methods such as numerical fitting are required to estimate the emittance, which introduces significant systematic errors. Data processing methods such as the adaptive ellipse elimination method are typically used to determine the emittance of a two-dimensional beam in either the horizontal or vertical directions.

[0046] The TEM grid (Transmission Electron Microscopy Grid) is similar to the pepper pot technique, which allows the particle beam to pass through a grid with square holes and form a projection on the observation screen downstream of the grid. Due to the momentum divergence of the particle beam, the projection of the grid line edge on the observation screen will show a blurred transition. By analyzing the position, width and brightness of these grid edges, the phase space distribution of the particle beam can be inferred. This method can improve the particle pass rate while reducing the suppression effect of the beam space charge effect. It is particularly suitable for low-energy electron beam emittance measurement with extremely low charge (0.1pC-1pC). However, there are the following problems:

[0047] 1. The spacing between adjacent microapertures in the microaperture array used in the pepper pot method must be large enough to prevent beamlets from overlapping at the downstream imaging module. Generally, the spacing between adjacent microapertures should be on the order of millimeters. Therefore, the pepper pot method cannot obtain a complete beam phase space distribution, affecting the emittance measurement accuracy.

[0048] 2. For high-brightness electron beams with energies of 1-10 MeV, single-bunch charges of 100 pC, and normalized emittances less than 0.2 mm / mrad, micropore size must be less than 5 μm to minimize lateral divergence of subbunches caused by beam space charge effects. Producing these micropores in metal baffles (0.5 mm to 2 mm thick) requires high-power femtosecond laser processing with extremely high pulse energies, a technically challenging task. Currently, there are no published reports of instruments measuring emittances with diameters less than 5 μm.

[0049] 3. When using the TEM grid method for emittance measurement, the charge of a single bunch of the beam must be controlled at the pC level, and it cannot be directly applied to the emittance measurement of beams with large bunch charges (100pC to nC).

[0050] Figure 2 This is a partial schematic diagram of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention. Figure 3 Schematic diagram of a slit assembly in a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention. Figure 4 This is a schematic diagram of the structure of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided by an embodiment of the present invention, with reference to Figure 2 、 Figure 3 and Figure 4The embodiment of the present invention provides a beam four-dimensional emittance measuring instrument based on orthogonal slits, comprising a slit assembly 1, a fluorescence collection assembly 2, and a data processing assembly 3; the slit assembly 1 comprises a first slit plate 11 and a second slit plate 12 stacked along a first direction X, the first slit plate 11 comprising a first slit 111; the second slit plate 12 comprising a second slit 121, the first slit 111 extending along a second direction Y, the second slit 121 extending along a third direction Z, the first direction X, the second direction Y, and the third direction Z being perpendicular to each other, and the first direction X being perpendicular to the plane where the first slit plate 11 is located; a charged particle beam S enters the first slit plate 11 from a side away from the second slit plate 12 The charged particle beam S is emitted to the slit assembly 1, and forms a first beam group B after being transmitted through the first slit 111 to the second slit plate 12. The first beam group B forms a second beam group C after being transmitted through the second slit 121 to the fluorescence collection assembly 2; the fluorescence collection assembly 2 and the data processing assembly 3 are electrically connected, and the fluorescence collection assembly 2 includes a fluorescent screen 21 and an image acquisition module 22. The fluorescent screen 21 is used to receive the second beam group C and generate fluorescence. The image acquisition module 22 is used to collect the fluorescence image formed by the fluorescence excited by the second beam group C on the fluorescent screen 21. The data processing assembly 3 is used to calculate the phase space distribution of the beam according to the fluorescence image, and measure the emittance of the charged particle beam S according to the phase space distribution.

[0051] Specifically, the beam emittance measuring instrument provided by the embodiment of the present invention includes a slit assembly 1, a fluorescence collection assembly 2, and a data processing assembly 3. A first slit plate 11 and a second slit plate 12 are stacked along a first direction X. The slit assembly 1 includes the first slit plate 11 and the second slit plate 12. The first slit plate 11 includes a first slit 111 extending along a second direction Y, and the second slit plate 12 includes a second slit 121 extending along a third direction Z. The first direction X, the second direction Y, and the third direction Z are perpendicular to each other. A charged particle beam S emitted by a high-brightness photocathode microwave electron gun (not shown) is incident on the slit assembly 1 from a side of the first slit plate 11 away from the second slit plate 12. The charged particle beam S is incident on the first slit plate 11 to form an initial beam cluster A. After the initial beam group A is transmitted through the first slit plate 11, it forms the first beam group B and is incident on the second slit plate 12. After the first beam group B is transmitted through the second slit plate 12, it forms the second beam group C and is incident on the fluorescence collection component 2. The fluorescence collection component 2 is electrically connected to the data processing component 3. The fluorescence collection component 2 includes a fluorescent screen 21 and a graphic acquisition module 22. The fluorescent screen 21 is used to receive the second beam group C and generate fluorescence. The graphic acquisition module 22 is used to collect the fluorescence generated on the fluorescent screen 21 by the fluorescence excited by the second beam group C. The graphic acquisition module 22 is used to infer the phase space distribution corresponding to the second beam group based on the fluorescence image. Based on the images of all second beam groups, the phase space distribution of the entire beam group can be further given, and the emittance of the charged particle beam S can be given through numerical analysis.

[0052] Continue to refer Figure 3 The slit assembly 1 also includes a connecting piece 6 between the first slit plate 11 and the motor, and a support frame 7 for the first slit plate 11 and the second slit plate 12. Exemplarily, the first slit plate 11 and the second slit plate 12 are made of tungsten, copper or stainless steel, etc., which have a high melting point, high strength and high thermal conductivity.

[0053] The beam emittance measuring instrument provided by the embodiment of the present invention has the following features:

[0054] 1. The first slit plate 11 primarily cuts the charged particle beam S horizontally to reduce the influence of the horizontal space charge force on the beam cluster. The second slit plate 12 further cuts the sub-beam clusters B to further suppress the vertical space charge force.

[0055] 2. The first slit plate 11 and the second slit plate 12 can also be used independently. When used alone, they constitute a single slit scanning device that can measure the two-dimensional phase space distribution and emittance in the horizontal or vertical direction independently.

[0056] The beam emittance measuring instrument provided in an embodiment of the present invention sequentially divides the charged particle beam emitted by an electron gun by continuously using slits in different directions, so that only a very small number of particles bombard the fluorescent screen each time. After summarizing the phase space distribution corresponding to each sub-bunch, a relatively complete beam phase space distribution can be obtained, and the beam emittance value can be quantitatively given based on the phase space distribution.

[0057] Optionally, the size of the second beam group is greater than the width of the first slit.

[0058] Specifically, the distance L1 between the second slit plate 12 and the fluorescent screen 21 is as far as possible to ensure that the size of the second beam group C incident on the second slit plate 12 is larger than the width of the first slit 111. Preferably, the size of the second beam group C is larger than five times the width of the first slit 111 and the second slit 121.

[0059] Optionally, the width of the first slit 111 and the second slit 121 is greater than or equal to 10 micrometers.

[0060] Specifically, the lower limit of the first slit 111 and the second slit 121 depends on the machining process, and the upper limit of the slit width depends on the systematic error introduced by the space charge effect of the second beam group C. The width of the first slit 111 and the second slit 121 is greater than or equal to 10 microns.

[0061] Optionally, a drive assembly 4 is also included, which includes a first drive motor 41 and a second drive motor 42; the first drive motor 41 and the second drive motor 42 are mechanically connected to the first slit plate 11 and the second slit plate 12 respectively; the first drive motor 41 is used to control the stepping displacement of the first slit plate 11 along the third direction Z, and the second drive motor 42 is used to control the stepping displacement of the second slit plate 12 along the second direction Y.

[0062] Specifically, the orthogonal slit-based beam four-dimensional emittance meter provided in an embodiment of the present invention also includes a drive assembly 4, including a first drive motor 41 mechanically connected to the first slit plate 11, and a second drive motor 42 mechanically connected to the second slit plate 12. The first drive motor 41 controls the stepping displacement of the first slit plate 11 along the third direction Z, and the second drive motor 42 controls the stepping displacement of the second slit plate 12 along the second direction Y. The distance between the first slit plate 11 and the second slit plate 12 is as close as possible without affecting the normal operation of the first drive motor 41 and the second drive motor 42.

[0063] Optionally, the first drive motor 41 and the second drive motor 42 need to be used in conjunction with a high-precision grating ruler, and the repeatability of the translation stage must be one order of magnitude lower than the width of the first slit 111 and the second slit 121 .

[0064] The thickness and material of the first slit plate 11 and the second slit plate 12 in the orthogonal slit-based four-dimensional emittance measurement instrument provided in the embodiment of the present invention need to comply with the following two principles:

[0065] Optionally, the signal-to-noise ratio of the second beam group C on the fluorescent screen 21 is greater than or equal to 3.

[0066] The thickness of the first slit plate 11 and the second slit plate 12 needs to ensure that the energy deposition of the electrons and secondary particles blocked and scattered at the first slit 111 and the second slit 121 on the downstream fluorescent screen is small enough, that is, to ensure that the signal-to-noise ratio of the second beam group C on the fluorescent screen 21 is greater than or equal to 3.

[0067] Optionally, the thickness of the first slit plate 11 and the second slit plate 12 also satisfies the requirement that the acceptance of the first slit 111 is greater than the root mean square emittance of the second beam cluster C.

[0068] The receptivity refers to the receiving capability or passing degree of the charged particle beam S by the first slit 111 or the second slit 121 ; the root mean square emittance (RMS emittance) is a measure that describes the distribution width of the charged particle beam in the phase space, reflecting the divergence and quality of the charged particle beam.

[0069] Specifically, the thicknesses of the first slit plate 11 and the second slit plate 12 satisfy that the acceptability of the first slit 111 is greater than the root mean square emittance of the second beam cluster C.

[0070] Optionally, the axis direction of the charged particle beam S is perpendicular to the plane where the fluorescent screen 21 is located.

[0071] Specifically, the second beam group C is observed by imaging the fluorescent screen 21. To improve imaging resolution and a larger field of view, the charged particle beam S is incident perpendicular to the fluorescent screen 21, that is, the axis direction of the charged particle beam S is perpendicular to the plane of the fluorescent screen 21.

[0072] Optionally, the fluorescence collection component 2 further includes a filter 221 ; the visible fluorescence signal excited by the second beam group C after passing through the fluorescent screen 21 passes through the filter 221 and is incident on the image collection module 22 .

[0073] Specifically, the fluorescence collection component 2 is further provided with a filter 221, which is used to adjust the fluorescence intensity received by the optical lens. The second beam group C is incident on the image collection module 22 through the filter 221; illustratively, the filter 221 can be a neutral density attenuation.

[0074] Optionally, the fluorescence collection assembly 2 further includes a reflector 222 ; the angle between the reflector 222 and the first direction X is 45°.

[0075] Specifically, the fluorescence collection assembly 2 further includes a reflector 222 , and the angle between the reflector 222 and the first direction X is 45°. The arrangement of the reflector 222 can further reduce the volume of the beam reflectivity measuring instrument provided by the embodiment of the present invention.

[0076] Optionally, the fluorescence collection component 2 further includes a lens 223 and a camera 224 .

[0077] According to the same inventive concept, Figure 5 This is a flow chart of a method for measuring the four-dimensional emittance of a beam based on orthogonal slits provided by an embodiment of the present invention. Figure 4 and Figure 5 An embodiment of the present invention provides a method for measuring beam four-dimensional emittance based on orthogonal slits. The beam emittance is measured using the beam four-dimensional emittance measuring instrument based on orthogonal slits in any of the above-mentioned embodiments of the invention. The measurement method includes:

[0078] S1, control the first slit plate to move along the third direction with the first step length d x Move to the first initial position Δx1; control the second slit plate to move along the second direction with a second step length d y Move to the second initial position Δy1.

[0079] Specifically, the first slit plate 11 is controlled to move along the third direction Z with a first step length d x Move to the first initial position Δx1, the first step length dx It can be set as needed; control the second slit plate to move along the second direction Y with a second step length d y Move to the second initial position Δy1.

[0080] S2 , controlling the charged particle beam S to be emitted to the fluorescent screen 21 through the first slit plate 11 and the second slit plate 12 .

[0081] Specifically, the charged particle beam S is emitted from the side of the first slit plate 11 away from the second slit plate 12 , and is emitted to the fluorescent screen 21 through the first slit plate 11 and the second slit plate 12 in sequence.

[0082] S3 , obtaining the projection distribution of the second beam group C carried on the fluorescent screen 21 in the third direction Z and the second direction Y.

[0083] Specifically, the charged particle beam S drifts through the first slit plate 11 and the second slit plate 12 and then hits the fluorescent screen 21. The image observed by the image acquisition module 22 determines the projection distribution δ (Δx i ,Δy j ).

[0084] S4. Determine the divergence angle distribution of the charged particle beam according to the projection distribution of the second beam group in the second direction Y and the third direction Z.

[0085] Specifically, according to the projection distribution δ(Δx i ,Δy j ) and the linear beam transport theory to determine the charged particle beam S at each position (Δx i ,Δy j ) is calculated as follows: ρ(Δx i , Δy j )=δ(Δx i , Δy j ) / L.

[0086] S5 , controlling the second slit plate 12 to perform multiple continuous step-by-step scans along the second direction Y, and calculating and obtaining the phase space distribution of the charged particle beam S.

[0087] Specifically, the second driving motor 42 is used to control the second slit plate 12 to perform step displacement along the second direction Y, and move to Δy in sequence. j (j=2, 3, 4, ..., N) positions, where N=(Δy max -Δy min ) / d y , and thus the charged particle beam S at position Δx is calculated i The phase space distribution I(Δx i, y, x', y').

[0088] S6 , controlling the first slit plate 11 to perform multiple continuous step-by-step scans along the third direction Z, and calculating and obtaining the phase space distribution of the charged particle beam S.

[0089] Specifically, the first driving motor 41 is used to control the first slit plate 11 to perform step displacement along the third direction Z, and move to Δx i (i=2, 3, 4, ..., M) positions, where M=(Δx max -Δx min ) / d x , and thus the charged particle beam S is calculated at the second initial position Δy j The phase space distribution I(x, Δy j , x', y').

[0090] S7. According to the phase space distribution of the charged particle beam S, the root mean square emittance of the charged particle beam S is determined by using an adaptive ellipse elimination method.

[0091] The adaptive ellipse elimination method is an advanced technique for optimizing emittance measurement data. Based on the property that the ideal beam phase space is usually contained within an ellipse, it uses multiple ellipses with the same eccentricity and slope calculated from the measured data to iteratively calculate the emittance, thereby finding the boundary between the beam data and the noise data. This results in more accurate emittance measurement results.

[0092] Specifically, ellipses with the same eccentricity and slope and increasing area are set. The emittance is calculated by taking the distribution inside the ellipse after deducting the mean of the distribution outside the ellipse. When the area of ​​the ellipse increases to the point where the size of the boundary between the useful signal and the noise interference signal is close, the rate of change of the emittance with the area of ​​the ellipse approaches zero. The emittance at this time is taken as the root mean square emittance of the beam.

[0093] S8. Calculate the emittance of the charged particle beam S based on the root mean square emittance.

[0094] Specifically, the ellipse exclusion method is used to analyze the valid data after the noise processing. Ellipses with the same eccentricity and slope are set. After finding the ellipse that contains 95% of the measured particles, the data outside the ellipse can be excluded and the 95% emittance of the charged particle beam can be calculated.

[0095] The beam emittance measuring instrument provided by the embodiment of the present invention can achieve the following effects:

[0096] 1. The size of the square micro-hole formed by the first slit plate and the second slit plate depends on the width of the two slits. Wire cutting, mechanical grinding, or laser processing can be used to produce a slit with a width of 10 microns. The size of the micro-hole can reach 10×10 square microns, which is at least an order of magnitude lower than the hole size produced by directly punching a metal plate.

[0097] 2. The space charge effect of the second beam is closely related to its size and charge. Because the microaperture formed by the first and second slit plates is smaller, the second beam passing through the microaperture has a small lateral size and low charge, resulting in weak space charge forces in the horizontal and vertical directions. This results in the second beam being essentially in a state of absolute emittance dominance. Beam dynamics simulations were used to evaluate the emittance measurement results using orthogonal double-slit scanning with a slit width of 10 microns, a slit thickness of 1 mm, and a slit spacing of 1 mm. Assuming a beam energy of 8 MeV, an RMS beam size of approximately 38-55 microns (Gaussian distribution) at the slit plates, and a longitudinal beam length of 5 picoseconds, particle-in-cell (PIC) simulations demonstrated that when the 100% emittance of the beam is greater than 0.16 mm.mrad, the measured 95% emittance error is less than 10%. When the measured beam emittance increases to approximately 0.3 mm.mrad, the emittance measurement deviation decreases to less than 1%. Figure 6 This is a beam error result diagram of a beam emittance measuring instrument provided by an embodiment of the present invention. The beam error result is shown in FIG. Figure 6 shown.

[0098] 3. The embodiment of the present invention has two working modes: for extremely small lateral emittance (less than 0.2 mm.mrad), an orthogonal double-slit scanning method is used for measurement to obtain a four-dimensional phase space distribution; for larger expected lateral emittance (greater than 0.3 mm.mrad), the emittance meter can also use a traditional single-slit (vertical slit or horizontal slit) scanning method to provide a two-dimensional phase space distribution and emittance in the vertical or horizontal direction in a faster scanning time.

[0099] 4. The beam is incident perpendicular to the fluorescent screen, and a reflector is placed downstream to transmit the visible light signal to the optical microscopy imaging system. This layout meets the Scheimpflug imaging condition. The Scheimpflug imaging condition is a technology used in photography, computer image processing, and visual measurement systems. It adjusts the tilt angle of the lens and image plane so that the object plane, image plane, and lens plane intersect in a straight line, thereby maintaining the same tilt angle for light entering the lens and image plane throughout the entire image area, thereby avoiding the influence of the fluorescent screen thickness on the imaging resolution.

[0100] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A beam four-dimensional emittance measuring instrument based on orthogonal slits, characterized in that: It includes a slit component, a fluorescence collection component and a data processing component; The slit assembly includes a first slit plate and a second slit plate stacked along a first direction, the first slit plate including a first slit; the second slit plate including a second slit, the first slit extending along a second direction, and the second slit extending along a third direction, the first direction, the second direction, and the third direction being perpendicular to each other, and the first direction being perpendicular to the plane on which the first slit plate is located; A charged particle beam is incident on the slit assembly from the side of the first slit plate away from the second slit plate. The charged particle beam is transmitted through the first slit to form a first beam group that is transmitted to the second slit plate. The first beam group is transmitted through the second slit to form a second beam group that is transmitted to the fluorescence collection assembly. The fluorescence collection component is electrically connected to the data processing component. The fluorescence collection component includes a fluorescent screen and an image collection module. The fluorescent screen is used to receive the second beam group and generate fluorescence. The image collection module is used to collect a fluorescent image emitted by the second beam group bombarding the fluorescent screen. The data processing component is used to calculate the phase space distribution of the beam based on the fluorescence image and measure the emittance of the charged particle beam based on the phase space distribution.

2. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 1, characterized in that: The size of the second beam group is greater than the width of the first slit.

3. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 1, characterized in that: The width of the first slit and the second slit is greater than or equal to 10 micrometers.

4. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 1, characterized in that: Also includes drive components, The driving assembly includes a first driving motor and a second driving motor; the first driving motor and the second driving motor are mechanically connected to the first slit plate and the second slit plate respectively; The first driving motor is used to control the first slit plate to move in a stepwise manner along the third direction, and the second driving motor is used to control the second slit plate to move in a stepwise manner along the second direction.

5. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 1, characterized in that: The signal-to-noise ratio of the second beam group on the fluorescent screen is greater than or equal to 3.

6. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 5, characterized in that: The thicknesses of the first slit plate and the second slit plate are also sufficient to ensure that the acceptance of the first slit is greater than the root mean square divergence angle of the second beam group.

7. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 1, characterized in that: The axis direction of the charged particle beam is perpendicular to the plane where the fluorescent screen is located.

8. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 1, characterized in that: The fluorescence collection component also includes a filter; The visible fluorescent signal excited by the second beam after passing through the fluorescent screen passes through the filter and is incident on the image acquisition module.

9. The beam four-dimensional emittance measuring instrument based on orthogonal slits according to claim 8, characterized in that: The fluorescence collection assembly also includes a reflector in a vacuum; The angle between the reflector and the first direction is 45°.

10. A method for measuring beam four-dimensional emittance based on orthogonal slits, comprising: measuring beam four-dimensional emittance using the orthogonal slit-based beam four-dimensional emittance measuring instrument according to any one of claims 1 to 9, wherein: The measuring method comprises: Control the first slit plate to move along the third direction with a first step length d x Move to the first initial position; control the second slit plate to move along the second direction with a second step length d y moving to a second initial position; controlling the charged particle beam to be emitted to the fluorescent screen through the first slit plate and the second slit plate; Acquire the projection distribution of the second beam group carried on the fluorescent screen in the third direction and the second direction; determining a divergence angle distribution of the charged particle beam according to a projection distribution of the second beam group in the second direction and the third direction; controlling the second slit plate to perform multiple continuous step-wise scans along the second direction to calculate the phase space distribution of the charged particle beam; controlling the first slit plate to perform a plurality of continuous step-wise scans along the third direction to calculate a phase space distribution of the charged particle beam; determining the root mean square emittance of the charged particle beam using an adaptive ellipse elimination method according to the phase space distribution of the charged particle beam; The emittance of the charged particle beam is calculated according to the root mean square emittance.

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