Method for measuring transverse emittance of specific energy beam of wide-energy-spectrum charged particle beam

Abstract

The invention relates to a wide-energy-spectrum charged particle beam specific energy beam transverse emittance measurement method, which is based on a quadrupole scanning method in beam transverse emittance measurement, and is characterized in that a group of orthogonally arranged dipoles are added as an auxiliary energy screening device; the transverse emittance of a narrow-band beam in a specific energy range in a wide-energy-spectrum charged particle beam is measured, the measurement requirement of the wide-energy-spectrum charged particle beam can be met through one system, the screening effect of dipoles can be utilized, the additional measurement error of the multi-energy beam when the emittance is measured through a quadrupole scanning method is reduced, and the measurement accuracy of the wide-energy-spectrum charged particle beam is improved. The method further improves the measurement precision of the emittance, and provides a feasible solution for the measurement of the transverse emittance of the beam in the formulated energy range of the wide-energy-spectrum charged particles.

Description

Technical Field

[0001] The present application relates to the field of charged particle beam quality testing, and in particular, to a method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam. Background Art

[0002] As a new type of physical detection, measurement and experimental means, charged particle beams are no longer limited to the field of theoretical physics research, but are gradually being applied to people's livelihood fields such as food production, medical diagnosis and treatment, as well as many scientific research fields such as materials, bioimaging, and radiation chemistry. In many application scenarios, the beam transverse emittance is one of the important parameters for measuring beam quality. In the field of charged particle beam parameter measurement, the quadrupole scanning method is a basic method for measuring the transverse emittance of charged particle beams. Its principle is based on the spatial charged particle beam transmission equation of Liouville's theorem. By repeatedly measuring the bunch size change information of the charged particle beam under different magnetic field transmission conditions, the characteristic parameters of the transmission equation in the transmission direction of the charged particle beam are obtained through the method of undetermined coefficients, and finally the transverse emittance of the charged particle beam is derived. In this process, when the charged particle beam is transmitted in space, each set of magnetic field size and direction, transmission distance and charged particle energy can uniquely determine the bunch size of a charged particle beam downstream. Multiple sets of magnetic fields correspond to multiple bunch sizes, and each transmission process is described by different transmission equations. When electromagnets are used to generate different transmission magnetic fields and the bunch size of the downstream charged particle beam is measured, multiple sets of transmission equations can be obtained, thereby realizing the aforementioned transverse emittance measurement of the charged particle beam.

[0003] At present, although the quadrupole scanning method has the advantages of large measurable range, fast measurement speed, and suitability for high-energy charged particle beams, the method needs to obtain the transmission equation of the charged particle beam according to the energy of the charged particle beam when solving the transverse emittance. Under ideal conditions, the charged particle beam has a single energy, and the derived transmission equation of the charged particle beam is applicable to all charged particles in the measurement process. At the same time, the transmission characteristics of charged particles of a single energy are consistent when passing through the quadrupole, and there is no chromatic aberration effect (i.e., the imaging difference of the charged particle bunch caused by energy difference) when measuring the bunch size, so the measurement accuracy of the bunch size is higher. However, in the usual measurement scenario, the energy of the charged particle beam has a certain distribution range. When measuring the transverse emittance of a narrow energy spectrum charged particle beam with a small energy distribution range, the measurement error caused by the energy difference can be ignored. However, when measuring the transverse emittance of a wide energy spectrum charged particle beam with a large energy distribution range, the transmission equation error and bunch size measurement error caused by the energy difference will have a greater impact, reducing the measurement accuracy of the quadrupole scanning method. On the other hand, for a charged particle beam with a wide energy spectrum, it may be necessary to measure the transverse emittance of particles in a specific energy range. This special requirement cannot be well achieved when using the traditional quadrupole scanning method. No matter how the traditional method chooses the test nominal energy, the measurement result is the statistical result of all energy charged particles, and it is impossible to distinguish the contribution and influence of each energy particle on the measurement result. Summary of the invention

[0004] In order to overcome at least one deficiency in the prior art, the present application provides a method for measuring the lateral emittance of a specific energy beam of a wide energy spectrum charged particle beam.

[0005] In a first aspect, a device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is provided, comprising: a charged particle beam source, an adjustable quadrupole, an energy slit, a dipole assembly, a fluorescent screen assembly, and a beam trash can; the dipole assembly comprises a horizontal dipole and a vertical dipole, the fluorescent screen assembly comprises a first fluorescent screen and a second fluorescent screen; the beam trash can is used to collect charged particle beams that are not involved in deflection;

[0006] The direction of the energy slit is determined according to the selected measurement direction of the transverse emittance of the beam to be measured; if the measurement direction of the transverse emittance is horizontal, the direction of the energy slit is horizontal; if the measurement direction of the transverse emittance is vertical, the direction of the energy slit is vertical;

[0007] The charged particle beam source continuously emits a charged particle beam to be measured. After the charged particle beam to be measured passes through the adjustable quadrupole, if the transverse emittance measurement direction is the horizontal direction, the charged particle beam to be measured passes through the energy slit and the vertical dipole, and forms an image at the center of the first fluorescent screen. If the transverse emittance measurement direction is the vertical direction, the charged particle beam to be measured passes through the energy slit and the horizontal dipole, and forms an image at the center of the second fluorescent screen.

[0008] The adjustable quadrupole is controlled by a bipolar adjustable DC power supply to generate scanning magnetic fields of different gradients to achieve regulation of the horizontal and vertical performance of the charged particle beam; the dipole assembly is used for energy spectrum broadening and energy screening, and the energy slit is used to eliminate the influence of the lateral size of the beam before energy spectrum broadening and energy screening; the magnetic field gradient of the quadrupole is changed by changing the excitation current of the adjustable quadrupole, so that the beam spot size on the fluorescent screen assembly changes, and the beam spot size and the corresponding excitation current of the adjustable quadrupole are used to calculate the lateral emittance of the charged particle beam.

[0009] In one embodiment, calculating the transverse emittance of a charged particle beam includes:

[0010] According to the recorded excitation currents and beam spot sizes of multiple sets of adjustable quadrupoles, the coefficients A and C in the charged particle beam transmission equation are determined by the least squares fitting method. The charged particle beam transmission equation is:

[0011]

[0012] f=k4I4

[0013] L d =L1+Rθ+L2

[0014] in, is the square of the beam spot size, A, B, C are coefficients, L d is the total distance the beam freely drifts after passing through the adjustable quadrupole, f is the magnetic focal length of the adjustable quadrupole, I4 is the excitation current of the adjustable quadrupole, k4 is the proportionality coefficient, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the phosphor screen;

[0015] To calculate the transverse emittance of a charged particle beam, the following formula is used:

[0016]

[0017] Where ε is the transverse emittance of the charged particle beam.

[0018] In one embodiment, the first fluorescent screen and the second fluorescent screen are both rectangular.

[0019] In a second aspect, a method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is provided, comprising:

[0020] Step S1, determining the required magnetic field induction intensity of the dipole component according to the energy of the charged particle beam to be measured; determining the electromagnet excitation current according to the magnetic field induction intensity; and setting the excitation current of the dipole component according to the electromagnet excitation current;

[0021] Step S2, selecting a transverse emittance measurement direction of the beam to be measured, and determining the direction of the energy slit according to the transverse emittance measurement direction; if the transverse emittance measurement direction is a horizontal direction, the direction of the energy slit is a horizontal direction; if the transverse emittance measurement direction is a vertical direction, the direction of the energy slit is a vertical direction;

[0022] Step S3, the charged particle beam source continuously emits the charged particle beam to be measured, and after the charged particle beam to be measured passes through the adjustable quadrupole, if the lateral emittance measurement direction is the horizontal direction, the charged particle beam to be measured passes through the energy slit and the vertical dipole, and is imaged in the center of the first fluorescent screen; if the lateral emittance measurement direction is the vertical direction, the charged particle beam to be measured passes through the energy slit and the horizontal dipole, and is imaged in the center of the second fluorescent screen;

[0023] Step S4, changing the excitation current of the adjustable quadrupole and recording the beam spot size on the phosphor screen assembly;

[0024] Step S5, calculating the lateral emittance of the charged particle beam according to the beam spot size on the phosphor screen assembly and the corresponding excitation current of the adjustable quadrupole;

[0025] Step S6, changing the lateral emittance measurement direction, and returning to step S2, until all lateral emittance measurement directions are measured;

[0026] Step S7, changing the energy of the charged particle beam to be measured, and returning to step S1.

[0027] In one embodiment, calculating the transverse emittance of a charged particle beam includes:

[0028] According to the recorded excitation currents and beam spot sizes of multiple sets of adjustable quadrupoles, the coefficients A and C in the charged particle beam transmission equation are determined by the least squares fitting method. The charged particle beam transmission equation is:

[0029]

[0030] f=k4I4

[0031] L d =L1+Rθ+L2

[0032] in, is the square of the beam spot size, A, B, C are coefficients, L d is the total distance the beam freely drifts after passing through the adjustable quadrupole, f is the magnetic focal length of the adjustable quadrupole, I4 is the excitation current of the adjustable quadrupole, k4 is the proportionality coefficient, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the phosphor screen;

[0033] To calculate the transverse emittance of a charged particle beam, the following formula is used:

[0034]

[0035] Where ε is the transverse emittance of the charged particle beam.

[0036] In one embodiment, the required magnetic field induction intensity of the dipole component is determined according to the energy of the charged particle beam to be measured, using the following formula:

[0037]

[0038] Among them, B2 is the magnetic field induction intensity, E0 is the energy of the charged particle beam to be measured, m0 is the mass of the charged particle, c is the speed of light, e is the charge of the charged particle, and R is the deflection radius;

[0039] Determine the electromagnet excitation current according to the magnetic field induction intensity, using the following formula:

[0040] I2=B2 / k2

[0041] Among them, I2 is the electromagnet excitation current and k2 is the proportional coefficient.

[0042] Compared with the prior art, the present application has the following beneficial effects: the method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam of the present application is based on the quadrupole scanning method in the beam transverse emittance measurement, and realizes the transverse emittance measurement of a narrow-band particle beam within a specific energy range in a wide energy spectrum charged particle beam by adding a group of orthogonally arranged dipoles as an auxiliary energy screening device. It can not only use a set of systems to meet the measurement requirements of the transverse emittance of a wide energy spectrum charged particle beam, but also use the screening effect of the dipoles to reduce the additional measurement errors of charged particle beams of various energies when measuring the transverse emittance using the quadrupole scanning method, further improve the measurement accuracy of the transverse emittance of the charged particle beam, and provide a feasible solution for the transverse emittance measurement of a wide energy spectrum charged particle beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present application may be better understood by referring to the following description given in conjunction with the accompanying drawings, which together with the following detailed description are included in this specification and form a part of this specification. In the drawings:

[0044] Figure 1 A top view of a device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is shown;

[0045] Figure 2 A side view of a device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is shown;

[0046] Figure 3 A schematic diagram of the energy slit is shown;

[0047] Figure 4 A schematic diagram showing the deflection of a beam of charged particles to be measured in a dipole is shown;

[0048] Figure 5 The flowchart of the method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is shown. DETAILED DESCRIPTION

[0049] The exemplary embodiments of the present application will be described below in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all features of the actual embodiments are described in the specification. However, it should be understood that many implementation-specific decisions can be made in the process of developing any such actual embodiments in order to achieve the specific goals of the developer, and these decisions may vary from embodiment to embodiment.

[0050] It is also necessary to explain here that, in order to avoid obscuring the present application due to unnecessary details, only the device structure closely related to the scheme according to the present application is shown in the drawings, while other details that are not closely related to the present application are omitted.

[0051] It should be understood that the present application is not limited to the described implementation forms due to the following description with reference to the accompanying drawings. In this article, where feasible, the embodiments can be combined with each other, features between different embodiments can be replaced or borrowed, and one or more features can be omitted in one embodiment.

[0052] The embodiment of the present application provides a device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam, which is improved on the basis of the existing quadrupole scanning method technology, and increases its measurement function of the transverse emittance of a specific energy beam in a wide energy spectrum charged particle beam, while improving the measurement accuracy of the transverse emittance of a charged particle beam by the quadrupole scanning method. By adding a set of dipoles with orthogonal magnetic field directions and placed in front and behind as energy screening components for the charged particle beam in the vacuum drift section between the quadrupole and the fluorescent screen, and replacing the traditional small-sized fluorescent screen (mostly circular) with a larger rectangular fluorescent screen, and supplemented with auxiliary components such as slits, the emittance measurement device of the present application is formed together. The entire device utilizes two important characteristics: the deflection of the charged particles by the magnetic field does not change their energy and the transverse emittance measurement and energy screening of the charged particles do not interfere with each other. When using the quadrupole scanning method, the change in the size of the charged particle beam bunch under different excitation currents and in the direction to be measured (horizontal or vertical direction) is the basis for calculating the transverse emittance of the charged particle beam. The regulation of the horizontal or vertical performance of the charged particle beam by the quadrupole has an effect on charged particles of all energies, and the degree of size change is related to its energy. Therefore, a dipole is added as an energy screening device during the drift of the charged particle beam, and a specific dipole excitation current is set. Only charged particle beams in a specific energy range are selected to pass through, and the beam spot size is measured. Finally, the transverse emittance measurement of a charged particle beam with a specific energy is finally realized by combining the three parameters of the quadrupole excitation current, the energy of the screened charged particle beam, and the obtained beam spot size. Since the transverse emittance measurement is directional, a set of two orthogonal magnetic fields is required to realize the transverse emittance measurement in two directions.

[0053] Figure 1 A top view of a device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is shown. Figure 2 A side view of a device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is shown, see Figure 1 and Figure 2 The device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam comprises: a charged particle beam source, an adjustable quadrupole, an energy slit, a dipole assembly, a fluorescent screen assembly and a beam trash can; the dipole assembly comprises a horizontal dipole and a vertical dipole, the fluorescent screen assembly comprises a first fluorescent screen and a second fluorescent screen; the beam trash can is used to collect charged particle beams that are not involved in deflection to reduce radiation impact;

[0054] The direction of the energy slit is determined according to the selected measuring direction of the transverse emittance of the beam to be measured; if the measuring direction of the transverse emittance is horizontal, the direction of the energy slit is horizontal; if the measuring direction of the transverse emittance is vertical, the direction of the energy slit is vertical; Figure 3 A schematic diagram of the energy slit is shown.

[0055] The charged particle beam source continuously emits a charged particle beam to be measured. After the charged particle beam to be measured passes through the adjustable quadrupole, if the lateral emittance measurement direction is the horizontal direction, the charged particle beam to be measured passes through the energy slit and the vertical dipole, and is imaged in the center of the first fluorescent screen. If the lateral emittance measurement direction is the vertical direction, the charged particle beam to be measured passes through the energy slit and the horizontal dipole, and is imaged in the center of the second fluorescent screen. Here, the charged particle beam to be measured is deflected after entering the vertical dipole or the horizontal dipole. Figure 4 A schematic diagram showing the deflection of the charged particle beam to be measured in a dipole is shown.

[0056] The adjustable quadrupole is controlled by a bipolar adjustable DC power supply to generate scanning magnetic fields of different gradients to achieve regulation of the horizontal and vertical performance of the charged particle beam. The dipole assembly is used for energy spectrum broadening and energy screening, and the energy slit is used to eliminate the influence of the lateral size of the beam before energy spectrum broadening and energy screening. The magnetic field gradient of the quadrupole is changed by changing the excitation current of the adjustable quadrupole, so that the beam spot size on the fluorescent screen assembly changes. The beam spot size and the corresponding excitation current of the adjustable quadrupole are used to calculate the lateral emittance of the charged particle beam.

[0057] In this embodiment, the device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam uses a dipole assembly, including two dipoles, namely a horizontal dipole and a vertical dipole. The horizontal dipole and the vertical dipole can be respectively arranged in two branches of a vacuum pipeline, and the horizontal dipole is correspondingly connected to the second fluorescent screen, and the vertical dipole is correspondingly connected to the first fluorescent screen, and the two branches are respectively used for the measurement when the transverse emittance measurement direction is the vertical direction and the measurement when the transverse emittance measurement direction is the horizontal direction. The magnetic field directions of the above two dipoles are orthogonally configured, and the energy measurement and the transverse emittance measurement in two directions can be completed simultaneously, without the need to reassemble the equipment, without destroying the integrity of the vacuum chamber, and improving the test measurement efficiency.

[0058] In addition, the adjustable quadrupole generates scanning magnetic fields with different gradients to achieve the regulation of the horizontal and vertical performance of the charged particle beam; the horizontal / vertical two groups of dipoles provide a uniform magnetic field to deflect the charged particle beam. The deflection radius of particles with different energies is proportional to the magnetic field strength. The dipole also uses an electromagnet to change the magnetic field strength, thereby achieving energy spectrum broadening and energy screening. Through the energy screening effect of the dipole component, the energy of the charged particles imaged on the fluorescent screen is basically uniform, reducing the beam spot size deviation caused by over-focusing or under-focusing of charged particles with non-nominal energy, which is conducive to improving the measurement accuracy of the quadrupole scanning method. The fluorescent screen component realizes beam fluorescence imaging, and the beam spot formed is the basis for measuring the size of the charged particle beam bunch. Other auxiliary equipment includes vacuum pipelines, which are used to provide the ultra-high vacuum environment required for beam transmission; orthogonal slits are used to eliminate the influence of the lateral size of the beam spot before energy spectrum broadening and energy screening, ensuring that only the core particles of the charged particle beam enter the subsequent measurement system; beam trash cans are used to collect other undeflected beams to reduce radiation effects.

[0059] According to the beam transmission theory, the original beam spot size Transverse emittance ε of charged particle beam and beam spot size on the phosphor screen The following relationship exists:

[0060]

[0061] in, is the square of the beam spot size, is the square of the original beam spot size, L d is the total distance the beam drifts freely after passing through the quadrupole, L d =L1+Rθ+L2, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the fluorescent screen; It represents the direction and degree of the beam spot phase ellipse, f is the magnetic focal length of the adjustable quadrupole, and ε is the lateral emittance of the charged particle beam.

[0062] Substituting variables for the above transmission relationship gives:

[0063]

[0064] Among them, A, B, and C are coefficients.

[0065] Specifically, the calculation of the transverse emittance of the charged particle beam includes:

[0066] According to the recorded excitation currents and beam spot sizes of multiple sets of adjustable quadrupoles, the coefficients A and C in the charged particle beam transmission equation are determined by the least squares fitting method. The charged particle beam transmission equation is:

[0067]

[0068] f=k4I4

[0069] L d =L1+Rθ+L2

[0070] in, is the square of the beam spot size, A, B, C are coefficients, L d is the total distance the beam freely drifts after passing through the adjustable quadrupole, f is the magnetic focal length of the adjustable quadrupole, I4 is the excitation current of the adjustable quadrupole, k4 is the proportionality coefficient, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the phosphor screen;

[0071] To calculate the transverse emittance of a charged particle beam, the following formula is used:

[0072]

[0073] Where ε is the transverse emittance of the charged particle beam.

[0074] The present application also provides a method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam. Figure 5 The flowchart of the method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam is shown in FIG. Figure 5 , methods include:

[0075] Step S1, according to the energy of the charged particle beam to be measured, determine the magnetic field induction intensity of the required dipole component; determine the electromagnet excitation current according to the magnetic field induction intensity; set the excitation current of the dipole component according to the electromagnet excitation current, and emit the charged particle beam for a short time to ensure that the beam can be correctly imaged in the center of the fluorescent screen.

[0076] Specifically, in order to ensure that the charged particle beam to be measured is deflected exactly to the center of the fluorescent screen, the magnetic field induction intensity of the required dipole component is determined according to the action of the Lorentz force and the relativistic effect, and the following formula is used:

[0077]

[0078] Among them, B2 is the magnetic field induction intensity, E0 is the energy of the charged particle beam to be measured, m0 is the mass of the charged particle, c is the speed of light, e is the charge of the charged particle, and R is the deflection radius;

[0079] Determine the electromagnet excitation current according to the magnetic field induction intensity, using the following formula:

[0080] I2=B2 / k2

[0081] Among them, I2 is the electromagnet excitation current, k2 is the proportional coefficient, and the proportional coefficient k2 is related to the measurement system design.

[0082] Step S2, select the transverse emittance measurement direction of the beam to be measured, and determine the direction of the energy slit according to the transverse emittance measurement direction; if the transverse emittance measurement direction is horizontal, the direction of the energy slit is horizontal; if the transverse emittance measurement direction is vertical, the direction of the energy slit is vertical.

[0083] Step S3, the charged particle beam source continuously emits the charged particle beam to be measured. After the charged particle beam to be measured passes through the adjustable quadrupole, if the lateral emittance measurement direction is the horizontal direction, the charged particle beam to be measured passes through the energy slit and the vertical dipole, and is imaged in the center of the first fluorescent screen. If the lateral emittance measurement direction is the vertical direction, the charged particle beam to be measured passes through the energy slit and the horizontal dipole, and is imaged in the center of the second fluorescent screen.

[0084] Step S4, changing the excitation current of the adjustable quadrupole and recording the beam spot size on the phosphor screen assembly.

[0085] Step S5, calculating the lateral emittance of the charged particle beam according to the beam spot size on the phosphor screen assembly and the corresponding excitation current of the adjustable quadrupole.

[0086] Specifically, the calculation of the transverse emittance of the charged particle beam includes:

[0087] According to the recorded excitation currents and beam spot sizes of multiple sets of adjustable quadrupoles, the coefficients A and C in the charged particle beam transmission equation are determined by the least squares fitting method. The charged particle beam transmission equation is:

[0088]

[0089] f=k4I4

[0090] L d =L1+Rθ+L2

[0091] in, is the square of the beam spot size, A, B, C are coefficients, L d is the total distance the beam freely drifts after passing through the adjustable quadrupole, f is the magnetic focal length of the adjustable quadrupole, I4 is the excitation current of the adjustable quadrupole, k4 is the proportionality coefficient, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the phosphor screen;

[0092] To calculate the transverse emittance of a charged particle beam, the following formula is used:

[0093]

[0094] Where ε is the transverse emittance of the charged particle beam.

[0095] Step S6, changing the lateral emittance measurement direction, and returning to step S2, until all lateral emittance measurement directions are measured;

[0096] Step S7, changing the energy of the charged particle beam to be measured, and returning to step S1. Here, the above measurement steps are performed according to the energy of the new charged particle beam to be measured.

[0097] Compared with the prior art, this application has the following technical effects:

[0098] The present application is based on the quadrupole scanning method in the transverse emittance measurement of charged particle beams. By adding a group of orthogonally arranged dipoles as an auxiliary energy screening device, the transverse emittance measurement of a narrow-band charged particle beam within a specific energy range in a wide energy spectrum charged particle beam is achieved. The present application can not only use a set of systems to meet the measurement requirements of the transverse emittance of a wide energy spectrum charged particle beam, but also use the screening effect of the dipoles to reduce the additional measurement errors of charged particle beams with multiple energies when using the quadrupole scanning method to measure the transverse emittance, further improve the measurement accuracy of the transverse emittance of a high-charged particle beam, and provide a feasible solution for the transverse emittance measurement of a wide energy spectrum charged particle beam.

[0099] The above are only various implementations of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A device for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam, characterized in that: include: A charged particle beam source, an adjustable quadrupole, an energy slit, a dipole assembly, a fluorescent screen assembly and a beam trash can; the dipole assembly includes a horizontal dipole and a vertical dipole, the fluorescent screen assembly includes a first fluorescent screen and a second fluorescent screen; the beam trash can is used to collect charged particle beams that are not involved in deflection; The direction of the energy slit is determined according to the selected measurement direction of the transverse emittance of the beam to be measured; if the measurement direction of the transverse emittance is horizontal, the direction of the energy slit is horizontal; if the measurement direction of the transverse emittance is vertical, the direction of the energy slit is vertical; The charged particle beam source continuously emits a charged particle beam to be measured. After the charged particle beam to be measured passes through the adjustable quadrupole, if the transverse emittance measurement direction is a horizontal direction, the charged particle beam to be measured passes through the energy slit and the vertical dipole, and is imaged at the center of the first fluorescent screen. If the transverse emittance measurement direction is a vertical direction, the charged particle beam to be measured passes through the energy slit and the horizontal dipole, and is imaged at the center of the second fluorescent screen. The adjustable quadrupole is controlled by a bipolar adjustable direct current power supply and is used to generate scanning magnetic fields of different gradients to achieve regulation of the horizontal and vertical performance of the charged particle beam; the dipole assembly is used for energy spectrum broadening and energy screening, and the energy slit is used to eliminate the influence of the lateral size of the beam before energy spectrum broadening and energy screening; the magnetic field gradient of the quadrupole is changed by changing the excitation current of the adjustable quadrupole, so that the beam spot size on the fluorescent screen assembly changes, and the beam spot size and the corresponding excitation current of the adjustable quadrupole are used to calculate the lateral emittance of the charged particle beam.

2. The device according to claim 1, characterized in that The step of calculating the transverse emittance of a charged particle beam comprises: According to the recorded excitation currents and beam spot sizes of multiple sets of adjustable quadrupoles, the coefficients A and C in the charged particle beam transmission equation are determined by using the least squares fitting method. The charged particle beam transmission equation is: f=k4I4 L d =L1+Rθ+L2 in, is the square of the beam spot size, A, B, C are coefficients, L d is the total distance the beam freely drifts after passing through the adjustable quadrupole, f is the magnetic focal length of the adjustable quadrupole, I4 is the excitation current of the adjustable quadrupole, k4 is the proportionality coefficient, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the phosphor screen; To calculate the transverse emittance of a charged particle beam, the following formula is used: Where ε is the transverse emittance of the charged particle beam.

3. The device according to claim 1, characterized in that The first fluorescent screen and the second fluorescent screen are both rectangular.

4. A method for measuring the transverse emittance of a specific energy beam of a wide energy spectrum charged particle beam, characterized in that: include: Step S1, determining the magnetic field induction intensity of the required dipole component according to the energy of the charged particle beam to be measured; Determining the electromagnet excitation current according to the magnetic field induction intensity; Setting the excitation current of the dipole component according to the electromagnet excitation current; Step S2, selecting a measurement direction of the transverse emittance of the beam to be measured, and determining the direction of the energy slit according to the measurement direction of the transverse emittance; If the lateral emittance measurement direction is a horizontal direction, the direction of the energy slit is a horizontal direction; if the lateral emittance measurement direction is a vertical direction, the direction of the energy slit is a vertical direction; Step S3, the charged particle beam source continuously emits a charged particle beam to be measured, and after the charged particle beam to be measured passes through the adjustable quadrupole, if the lateral emittance measurement direction is the horizontal direction, the charged particle beam to be measured passes through the energy slit and the vertical dipole, and is imaged in the center of the first fluorescent screen; if the lateral emittance measurement direction is the vertical direction, the charged particle beam to be measured passes through the energy slit and the horizontal dipole, and is imaged in the center of the second fluorescent screen; Step S4, changing the excitation current of the adjustable quadrupole and recording the beam spot size on the phosphor screen assembly; Step S5, calculating the lateral emittance of the charged particle beam according to the beam spot size on the phosphor screen assembly and the corresponding excitation current of the adjustable quadrupole; Step S6, changing the lateral emittance measurement direction, and returning to step S2, until all lateral emittance measurement directions are measured; Step S7, changing the energy of the charged particle beam to be measured, and returning to step S1.

5. The method according to claim 4, characterized in that The step of calculating the transverse emittance of a charged particle beam comprises: According to the recorded excitation currents and beam spot sizes of multiple sets of adjustable quadrupoles, the coefficients A and C in the charged particle beam transmission equation are determined by using the least squares fitting method. The charged particle beam transmission equation is: f=k4I4 L d =L1+Rθ+L2 in, is the square of the beam spot size, A, B, C are coefficients, L d is the total distance the beam freely drifts after passing through the adjustable quadrupole, f is the magnetic focal length of the adjustable quadrupole, I4 is the excitation current of the adjustable quadrupole, k4 is the proportionality coefficient, L1 is the distance from the adjustable quadrupole to the dipole assembly, Rθ is the deflection distance in the dipole assembly, R is the deflection radius, θ is the rotation angle, and L2 is the distance from the dipole assembly to the phosphor screen; To calculate the transverse emittance of a charged particle beam, the following formula is used: Where ε is the transverse emittance of the charged particle beam.

6. The method according to claim 4, characterized in that in, According to the energy of the charged particle beam to be measured, the magnetic field induction intensity of the required dipole component is determined using the following formula: Among them, B2 is the magnetic field induction intensity, E0 is the energy of the charged particle beam to be measured, m0 is the mass of the charged particle, c is the speed of light, e is the charge of the charged particle, and R is the deflection radius; The electromagnet excitation current is determined according to the magnetic field induction intensity using the following formula: I2=B2 / k2 Among them, I2 is the electromagnet excitation current and k2 is the proportional coefficient.

Images