Beam four-dimensional emittance measuring instrument and measuring method based on orthogonal slit

Abstract

The invention discloses a beam four-dimensional emittance measuring instrument and measuring method based on an orthogonal slit, and the method comprises the steps: enabling a charged particle beam to enter a slit assembly from one side, far away from a second slit plate, of a first slit plate, and enabling the charged particle beam to form a first beam cluster to the second slit plate after the charged particle beam is transmitted through the first slit; the first beam group is transmitted by the second slit to form a second beam group to the fluorescence acquisition assembly; the fluorescence acquisition assembly comprises a fluorescent screen and an image acquisition module, the fluorescent screen is used for receiving the second beam group and generating fluorescence, the image acquisition module is used for acquiring a fluorescence pattern emitted by the fluorescent screen bombarded by the second beam group, and the data processing assembly is used for calculating phase space distribution of beams according to the fluorescence image. And measuring the emittance of the charged particle beam according to the phase space distribution. According to the beam four-dimensional emittance measuring instrument provided by the invention, the beam is segmented through the slits in the orthogonal direction, so that more complete four-dimensional phase space distribution can be obtained, and the measurement integrity and precision of the beam emittance are improved.

Description

Technical Field

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

[0002] High brightness photocathode microwave electron gun is one of the most critical parts to drive advanced synchrotron radiation sources and free electron laser devices. In order to achieve saturated light emission of future high gain free electron laser devices, it is generally required that the electron beam generated by the photocathode microwave electron gun has characteristics such as charge of 100 picoules and normalized emittance less than 0.2 mm.mrad. Beam emittance refers to the phase space area occupied by the beam in the beam phase space composed of the position coordinates x and momentum px of the particles in the beam. The emittance is proportional to the beam size and the angle of flare, and the unit is generally mm.mrad. When measuring the emittance in practice, it can also be calculated using the phase space composed of the position coordinates x and the divergence angle x'. The emittance can be calculated by statistical methods based on the given phase space distribution, and the calculated emittance is the root mean square emittance.

[0003] In order to accurately evaluate the performance and beam quality of the 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 the photocathode microwave electron gun is usually in the order of mega-electron volts (MeV). Due to the small lateral emittance, the beam is in a state dominated by space charge. The emittance measurement method based on linear optics generally has large measurement errors. Therefore, it is crucial to control the measurement error introduced by the space charge effect for the accurate measurement of extremely small emittance. 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 realized. Therefore, it is necessary to use the percentage emittance (100% full emittance and the commonly used 95% emittance) calculated using information that only contains a certain percentage of particles in the center of the bunch.

[0004] For the beam generated by the photocathode microwave electron gun, the traditional emittance measurement methods mainly include single slit scanning method, multi-slit method, pepper pot method and TEM grid method, etc. Among them, the single slit scanning method and the multi-slit method can only realize the two-dimensional beam phase space distribution and emittance measurement, while the pepper pot method and the TEM grid method can realize four-dimensional phase space measurement, which uses some regularly arranged micro-hole array grid arrays to divide the beam into several sub-bunches, which have low charge and are in an emittance-dominated state, so as to control the emittance growth introduced by the space charge effect within an acceptable range (generally less than 10%).

[0005] However, the spacing between adjacent microholes in the microhole array used in the pepper pot method must be large enough to prevent the sub-beams from overlapping each other at the downstream imaging module. Generally speaking, the spacing between adjacent microholes should be several times the size of the microholes. Therefore, the pepper pot method cannot obtain a complete beam phase space distribution, affecting the emittance measurement accuracy. Summary of the invention

[0006] The present invention provides a beam four-dimensional emittance measuring instrument and a measuring method based on orthogonal slits. The charged particle beam emitted by an electron gun is divided in sequence by continuously using slits in different directions, so that only 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 according to 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 orthogonal slits, comprising a slit component, a fluorescence collection component and a data processing component;

[0008] The slit assembly comprises a first slit plate and a second slit plate stacked along a first direction, the first slit plate comprises a first slit; the second slit plate comprises a second slit, the first slit extends along a second direction, the second slit extends along a third direction, the first direction, the second direction and the third direction are perpendicular to each other, and the first direction is perpendicular to the plane where 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 to the second slit plate, and the first beam group is transmitted through the second slit to form a second beam group 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 according to the fluorescence image, and measure the emittance of the charged particle beam according to 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, a drive assembly is also included.

[0014] The driving assembly comprises 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, a signal-to-noise ratio of the second beam group on the fluorescent screen is greater than or equal to 3.

[0017] Optionally, the thickness of the first slit plate and the second slit plate also satisfies 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 axial 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 is incident on the image acquisition module through the filter.

[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 the divergence angle distribution of the charged particle beam according to the 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-by-step scans along the second direction, and calculating and obtaining the phase space distribution of the charged particle beam;

[0029] Controlling the first slit plate to perform multiple continuous step-by-step scans along the third direction, and calculating the phase space distribution of the charged particle beam;

[0030] Determining the root mean square emittance of the charged particle beam using an adaptive ellipse exclusion 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 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 comprises a first slit; the second slit plate comprises a second slit, the first slit extends along a second direction, the second slit extends along a third direction, the first direction, the second direction and the third direction are perpendicular to each other, and the first direction is perpendicular to the plane where 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 to the second slit plate, and the first beam group is transmitted through the second slit to form a second beam group to the fluorescence collection assembly; the fluorescence collection assembly and the data processing assembly are electrically connected, the fluorescence collection assembly comprises 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, and the data processing assembly 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 according to the phase space distribution. The present invention provides a beam four-dimensional emittance measuring instrument and a measuring method based on orthogonal slits. The charged particle beam emitted by an electron gun is divided in sequence by continuously using slits in different directions, so that only 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 according to the phase space distribution.

[0033] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily 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 working diagram of measuring the emittance of a beam by the pepper pot method;

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

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

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

[0039] Figure 5 It is a flow chart of a beam four-dimensional emittance measurement method 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 in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme 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 described embodiments 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 creative work should fall within the scope of protection of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the specification 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 data 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 that are 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 processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0044] Figure 1 This is a working diagram of the pepper pot method for measuring the emittance of a beam. Figure 1 The 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 a strong laser pulse. In the prior art, there are various methods for measuring the electron beam emittance, such as the pepper pot method. The pepper pot method emittance measurement is based on the principle of splitting the beam in a horizontal two-dimensional plane (x, y), which can realize the four-dimensional emittance measurement of a single beam, such as Figure 1 As shown, the beam group to be measured emitted by the high brightness photocathode microwave electron gun passes through the pepper hole baffle S1 and then hits the fluorescent screen S2 after the emission distance L, wherein the beam direction is perpendicular to the direction of the fluorescent screen S2. The pepper holes used are evenly distributed on the pepper hole baffle S1 and arranged according to a preset dot matrix pattern. On the basis of ensuring that the beams passing through adjacent holes do not overlap, the beams pass through the small hole array and hit the fluorescent screen S2, and then the relative distribution of the beams can be measured using an optical imaging system.

[0045] Each hole position (x i ,y i ) corresponds 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 split 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 transmission theory, the beam lateral 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, which can determine the four-dimensional phase space distribution I (x i , x i ',y i ,y i '). It is worth pointing out that only a part of the particles can pass through the pepper hole, so the phase space distribution given is incomplete, and offline analysis methods such as numerical fitting are needed to estimate the emittance value. The systematic error introduced by this process cannot be ignored. For the horizontal or vertical two-dimensional beam emittance, data processing methods such as adaptive ellipse exclusion method are usually used to determine it.

[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 reduce the suppression effect of the beam space charge effect while improving the particle pass rate. 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 microholes in the microhole array used in the pepper pot method must be large enough to avoid overlapping of sub-beams at the downstream imaging module. Generally speaking, the spacing between adjacent microholes should be in the order of millimeters. Therefore, the pepper pot method cannot obtain a complete beam phase space distribution, which affects the accuracy of emittance measurement.

[0048] 2. For high-brightness electron beams with energies of 1-10 MeV, single bunch charge of 100 pC, and normalized emittance less than 0.2 mm.mrad, the micropore size must be less than 5 microns to reduce the lateral divergence of sub-bunches caused by the beam space charge effect. In order to produce micropores that meet the requirements on metal baffles (thickness 0.5 mm-2 mm), high-power femtosecond laser processing with extremely high pulse energy is required, which is technically difficult. At present, there are no public reports on the use of relevant emittance measuring instruments with a diameter less than 5 microns.

[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 is a partial schematic diagram of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided in an embodiment of the present invention, Figure 3 is a schematic diagram of a slit assembly in a beam four-dimensional emittance measuring instrument based on orthogonal slits provided in an embodiment of the present invention, Figure 4 is a schematic diagram of a beam four-dimensional emittance measuring instrument based on orthogonal slits provided in 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, including a slit assembly 1, a fluorescence collection assembly 2 and a data processing assembly 3; the slit assembly 1 includes a first slit plate 11 and a second slit plate 12 stacked along a first direction X, the first slit plate 11 includes a first slit 111; the second slit plate 12 includes a second slit 121, the first slit 111 extends along a second direction Y, and the second slit 121 extends along a third direction Z, the first direction X, the second direction Y and the third direction Z are perpendicular to each other, and the first direction X is 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 after being transmitted through the first slit 111, it forms a first beam group B to the second slit plate 12. After being transmitted through the second slit 121, the first beam group B forms a second beam group C to the fluorescence collection assembly 2. The fluorescence collection assembly 2 and the data processing assembly 3 are electrically connected. 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 second beam group C stimulating fluorescence 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. The first slit plate 11 and the 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. 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 in the figure) 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 group A. The initial beam group A is transmitted through the first slit plate 11 to form the first beam group B, which is incident on the second slit plate 12. The first beam group B is transmitted through the second slit plate 12 to form the second beam group C, which 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 excitation of 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. The phase space distribution of the entire beam group can be further given based on the images of all the second beam groups, 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 connector 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 characteristics of the beam emittance measuring instrument provided by the embodiment of the present invention are as follows:

[0054] 1. The first slit plate 11 mainly cuts the charged particle beam S horizontally to reduce the influence of the horizontal space charge force on the beam. The second slit plate 12 further cuts the sub-beam cluster 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, which 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 the embodiment of the present invention divides the charged particle beam emitted by the electron gun in sequence 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-beam bunch, a relatively complete beam phase space distribution can be obtained, and the beam emittance value can be quantitatively given according to 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 system 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 driving component 4 is also included, which includes a first driving motor 41 and a second driving motor 42; the first driving motor 41 and the second driving motor 42 are mechanically connected to the first slit plate 11 and the second slit plate 12 respectively; the first driving motor 41 is used to control the stepping displacement of the first slit plate 11 along the third direction Z, and the second driving motor 42 is used to control the stepping displacement of the second slit plate 12 along the second direction Y.

[0062] Specifically, the beam four-dimensional emittance measuring instrument based on orthogonal slits provided in an embodiment of the present invention also includes a driving component 4, including a first driving motor 41 mechanically connected to the first slit plate 11, and a second driving motor 42 mechanically connected to the second slit plate 12. The first driving motor 41 controls the stepping displacement of the first slit plate 11 along the third direction Z, and the second driving 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 driving motor 41 and the second driving 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 beam four-dimensional emittance measuring instrument based on orthogonal slits provided in the embodiment of the present invention need to comply with the following two principles:

[0065] Optionally, a 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 acceptance refers to the receiving capability or passing degree of the first slit 111 or the second slit 121 for the charged particle beam S; the root mean square emittance (RMS emittance) is a broad quantity 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 thickness of the first slit plate 11 and the second slit plate 12 satisfies that the acceptance of the first slit 111 is greater than the root mean square emittance of the second beam cluster C.

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

[0071] Specifically, the observation of the second beam group C adopts the imaging method of the fluorescent screen 21. In order to improve the imaging resolution and the larger field of view, the charged particle beam S is incident perpendicular to the fluorescent screen 21, that is, the axial direction of the charged particle beam S is perpendicular to the plane where the fluorescent screen 21 is located.

[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 also provided with a filter 221, and the filter 221 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 in the embodiment of the present invention.

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

[0077] According to the same inventive concept, Figure 5 is a flow chart of a beam four-dimensional emittance measurement method based on orthogonal slits provided by an embodiment of the present invention, with reference to Figure 4 and Figure 5 The embodiment of the present invention provides a method for measuring the four-dimensional emittance of a beam based on orthogonal slits, and the four-dimensional emittance measuring instrument for beam based on orthogonal slits in any of the above embodiments of the invention is used to measure the emittance of the beam. The measuring 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 a side of the first slit plate 11 away from the second slit plate 12 , and the charged particle beam S 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 obtaining the phase space distribution of the charged particle beam S by calculation.

[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. Control the first slit plate 11 to perform multiple continuous step-by-step scans along the third direction Z, and calculate 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] Among them, the adaptive ellipse exclusion method is an advanced technology used to optimize emittance measurement data. It is mainly based on the property that the ideal beam phase space is usually contained in an ellipse. It uses multiple ellipses with the same eccentricity and slope calculated from the measured data to gradually iterate and calculate the emittance, thereby finding the boundary between the beam data and the noise data. In this way, more accurate emittance measurement results can be obtained.

[0092] Specifically, ellipses with the same eccentricity and slope and areas from small to large are set, and the emittance is calculated by taking the distribution inside the ellipse after deducting the mean value of the distribution outside the ellipse. When the area of ​​the ellipse increases to the size close to the boundary between the useful signal and the noise interference signal, 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. The emittance of the charged particle beam S is calculated based on the root mean square emittance.

[0094] Specifically, the ellipse exclusion method is used to analyze the valid data after the noise processing, and ellipses with the same eccentricity and slope are set. After finding the ellipse in which 95% of the measured particles are contained, 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. A slit with a width of 10 microns can be manufactured by wire cutting, mechanical grinding or laser processing, and the size of the micro-hole can reach 10×10 square microns, which is at least one 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 group is closely related to the size and charge of the second beam group. Since the microhole formed by the first slit plate and the second slit plate is smaller in size, the second beam group passing through the microhole has a small lateral size and a low charge, and its space charge force in the horizontal and vertical directions is weak, and the second beam group is basically in an absolutely dominant state of emittance. The emittance measurement results of orthogonal double slit scanning with a slit width of 10 microns, a slit thickness of 1 mm, and a slit spacing of 1 mm were evaluated using beam dynamics simulation. Assuming that the beam energy is 8 MeV, the RMS size of the beam out of the slit plate is about 38-55 microns (Gaussian distribution), and the longitudinal length of the beam group is 5 picoseconds, the particle simulation method (Particle-In-Cell, PIC) shows 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 emittance of the beam to be measured increases to about 0.3 mm.mrad, the emittance measurement deviation is reduced to less than 1%, Figure 6 is a beam error result diagram of a beam emittance measuring instrument provided by an embodiment of the present invention. The beam result is as follows 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 inclination angle of the lens and the image plane so that the object plane, image plane and lens plane intersect in a straight line, thereby keeping the light entering the lens and image plane at the same inclination angle in the entire image area, which can avoid the influence of the fluorescent screen thickness on the imaging resolution.

[0100] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope 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 comprises a first slit plate and a second slit plate stacked along a first direction, the first slit plate comprises a first slit; the second slit plate comprises a second slit, the first slit extends along a second direction, the second slit extends along a third direction, the first direction, the second direction and the third direction are perpendicular to each other, and the first direction is perpendicular to the plane where 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 to the second slit plate, and the first beam group is transmitted through the second slit to form a second beam group 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 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 according to the fluorescence image, and measure the emittance of the charged particle beam according to 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 comprises 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 make the acceptance of the first slit 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 is incident on the image acquisition module through the filter.

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, using the beam four-dimensional emittance measuring instrument based on orthogonal slits as claimed in any one of claims 1 to 9 to measure beam four-dimensional emittance, characterized in that: 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 the divergence angle distribution of the charged particle beam according to the 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-by-step scans along the second direction, and calculating and obtaining the phase space distribution of the charged particle beam; Controlling the first slit plate to perform multiple continuous step-by-step scans along the third direction, and calculating the phase space distribution of the charged particle beam; Determining the root mean square emittance of the charged particle beam using an adaptive ellipse exclusion 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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