A positron capture system and method

Abstract

The application relates to a positron trapping system and method. The system comprises a trapping light source and a magnetic field deflection device; the trapping light source is used for forming a trapping electromagnetic field, so that the radial coordinate and radial momentum of a charged particle beam entering the trapping electromagnetic field are reduced and limited in a trapping area; the trapping light source is a left-handed circularly polarized Laguerre-Gaussian laser or a vector polarized light beam; there is a phase difference of pi / 2 between a radial electric field and a longitudinal electric field in the trapping electromagnetic field; the longitudinal electric field comprises a plurality of alternating longitudinal acceleration electric fields and longitudinal deceleration electric fields; the magnetic field deflection device is arranged in front of the trapping area and is used for separating positrons and electrons in the trapped charged particle beam to obtain a positron beam.

Description

Technical Field

[0001] This application relates to the field of charged particle capture technology, and in particular to a positron capture system and method. Background Technology

[0002] A positron is the antiparticle of the electron, possessing the same mass and an equal but opposite charge. When a positron enters the interior of matter, it annihilates with an electron, emitting a gamma photon. Positron annihilation technology can be used to obtain information about the internal structure and defects of matter, detecting changes in microstructure before alterations occur in the material's mechanical properties. Furthermore, the generation of positrons provides scientists with opportunities to study astronomical phenomena such as black holes and gamma-ray bursts in the laboratory, as well as the interaction of positrons and electrons with plasmas, positron elements, and Bose-Einstein condensates.

[0003] Currently, the commonly used positron sources in laboratories are radioisotope positron sources and accelerator positron sources. Radioisotope positron sources either have too short a half-life, limiting their transportation and use, or too low a source intensity, significantly reducing detection efficiency. While accelerator-based positron sources can greatly increase the beam intensity of positrons, accelerators are large and expensive.

[0004] With the continuous development of laser technology, petawatt-level and even petawatt-level ultra-intense laser devices have been or are about to be put into use, and laser-plasma interaction has become an important way to generate positron sources. Laser-driven positron generation is mainly based on three mechanisms: the Trident process, the Bethe-Heitler (BH) process, and the Breit-Wheeler (BW) process. The Trident process refers to the collision of a hyperthermic electron with a target nucleus to produce a virtual photon. This virtual photon generates an electron-positron pair under the influence of the Coulomb field of the target nucleus; the virtual photon only plays an intermediate conversion role. The BH process refers to the bremsstrahlung emission of hyperthermic electrons in a high atomic number (Z) target, producing a gamma photon with an energy of up to MeV. This high-energy gamma photon interacts with a high-Z target nucleus to produce an electron-positron pair. Due to the need for the participation of heavy atomic nuclei moving at extremely high speeds or ultra-high intensity lasers, research on the BW process mainly focuses on the theoretical aspects. The Trident and BH processes are the mainstream experimental research schemes.

[0005] Currently, experimental methods for generating positron beams can be divided into indirect and direct methods.

[0006] In the indirect approach, a high-quality electron beam is first generated by tail field acceleration. This high-quality electron beam then interacts with a second-stage high-Z solid target to produce a positron beam. Because tail field acceleration yields a higher-quality electron beam, the positron beam produced by the indirect approach typically has a higher temperature (approximately 28.8 MeV), a larger positron / γ ratio, and a smaller divergence angle.

[0007] In the direct approach, the laser interacts directly with a high-Z solid target. When the thermionic electrons generated by the laser interact with the high-Z target, positrons are typically produced via the BH or Trident process. Due to the higher electron density and the influence of the target normal sheath acceleration fields, positron beams from the direct approach exhibit higher yields and narrower energy spectra, thus possessing unique advantages. However, because the thermionic electrons used to generate positrons have large divergence angles, the positron beams produced by the direct approach typically have large divergence angles (usually >30°), which is the biggest drawback of the direct approach and severely hinders its application in various fields. Therefore, a suitable trapping scheme is urgently needed to collect positrons and optimize their quality.

[0008] Currently, the main methods for capturing positrons behind a target include flux concentrators, pulsed solenoids, and plasma lenses. Among these, flux concentrators and pulsed solenoids are the mainstream methods. Both of these methods use coils of specific shapes to generate magnetic fields with specific structures to laterally confine positrons. Theoretically, this approach can only restrict the lateral movement of positrons and cannot reduce their divergence angle, nor can it optimize the quality of the captured positron beam. Furthermore, because it is currently technically impossible to generate a stable and symmetrical capturing magnetic field structure, the focusing of positrons using this method is usually not radially symmetrical. Plasma lenses are a novel concept for capturing positrons behind a target, offering many advantages over flux concentrators and pulsed solenoids, such as radially symmetrical focusing of positrons. However, providing ultra-high vacuum and capturing positrons with extremely large divergence angles remain significant challenges for this new approach.

[0009] In summary, although laser-driven positron sources have many advantages over traditional methods, their excessive divergence angle severely limits their application prospects. Currently, there is limited research on trapping schemes specifically for laser positron sources, and traditional trapping schemes also suffer from drawbacks such as the inability to reduce the divergence angle and radial asymmetry in focusing. Therefore, there is an urgent need to develop novel trapping schemes. Summary of the Invention

[0010] Therefore, it is necessary to provide a positron capture system and method to address the aforementioned technical problems in order to capture positrons with large divergence angles.

[0011] A positron capture system, comprising:

[0012] A device for capturing light sources and deflecting magnetic fields;

[0013] The trapping light source is used to form a trapping electromagnetic field, which reduces the radial coordinates and radial momentum of the charged particle beam entering the trapping electromagnetic field and confines it to the trapping region; the trapping light source is a left-handed circularly polarized Laguerre Gaussian laser or a vector-polarized beam; there is a π / 2 phase difference between the radial electric field and the longitudinal electric field in the trapping electromagnetic field; the longitudinal electric field includes multiple alternating longitudinal accelerating electric fields and longitudinal decelerating electric fields;

[0014] A magnetic field deflection device is positioned in front of the capture area to separate positrons and electrons in the captured beam of charged particles to obtain a positron beam.

[0015] A positron capture method, comprising:

[0016] The trapping light source is turned on to form a trapping electromagnetic field; the trapping light source is a left-handed circularly polarized Laguerre Gaussian laser or a vector-polarized beam; there is a phase difference of π / 2 between the radial electric field and the longitudinal electric field in the trapping electromagnetic field; the longitudinal electric field includes multiple alternating longitudinal accelerating electric fields and longitudinal decelerating electric fields;

[0017] The radial electric field and multiple alternating longitudinal accelerating and decelerating electric fields reduce the radial coordinates and radial momentum of the charged particle beam entering the capturing electromagnetic field and confine it to the capturing region; a magnetic field deflection device is provided in front of the capturing region.

[0018] A positron beam is obtained by separating positrons and electrons from a captured beam of charged particles using a magnetic field deflection device.

[0019] In this invention, the forces exerted on charged particles injected into the capture region in the longitudinal and radial directions are always proportional to the longitudinal or radial electric field. Due to the π / 2 phase difference between the radial and longitudinal electric fields, the radial electric field is greater than zero in the first half of each longitudinal accelerating electric field. At this time, the positron experiences a radial force outward, and the positron is repelled. Conversely, the radial electric field is less than zero in the second half of each longitudinal accelerating electric field. At this time, the positron experiences a radial force inward, and the positron is focused inward. In other words, when a positron passes through each longitudinal accelerating region, it experiences half radial acceleration and half radial deceleration. Similarly, when a positron passes through each deceleration region, it also experiences half radial deceleration and half radial acceleration. Since the radial electric field gradually strengthens along the rising edge of the envelope, and the duration of the net radial force being positive is much shorter than the duration of being negative, the radial momentum and radial coordinate of the positron decrease significantly after passing through a longitudinal accelerating electric field and a longitudinal decelerating electric field. Throughout the process, the radial motion of the positron is similar to a damped oscillation. The radial electric force and magnetic field force provide the restoring force and damping force, respectively. The radial momentum and radial coordinate gradually decrease. Finally, the positron is confined to the trapping region and maintains a small radial momentum. Attached Figure Description

[0020] Figure 1A schematic diagram of a positron generation and capture system;

[0021] Figure 2 This is a schematic diagram of a positron capture method;

[0022] Figure 3 Analysis of the typical positron capture process and mechanism; Figure 3 (a) shows the evolution curves of the three radial field components experienced by a typical positron; Figure 3 (b) shows the evolution curves of the radial and longitudinal momentum of the positron over time; Figure 3 (c) shows the evolution curves of the radial and co-motion coordinates of the positron over time; Figure 3 (d) shows the radial and longitudinal electric field distributions of a left-handed circularly polarized Laguerre Gaussian laser pulse;

[0023] Figure 4 This is a schematic diagram of a positron capture scheme;

[0024] Figure 5 The results of particle simulations for a left-handed circularly polarized Laguerre Gaussian laser-accelerated positron beam; Figure 5 (a) shows the density distribution of the positron beam at time 5T0; Figure 5 (b) shows the density distribution of the positron beam at time 50T0; Figure 5 (c) shows the density distribution of the positron beam at time 150T0; Figure 5 (d) represents the evolution of the divergence angle of the positron over time; Figure 5 (e) shows the evolution of the energy spectrum of a positron over time;

[0025] Figure 6 The influence of initial radial position and the main acceleration mechanism of positrons; Figure 6 (a) is the normalized probability density of positrons being trapped at different initial radial positions r0; Figure 6 (b) When the value is 100T0, the captured positrons are in (η x ,η ⊥ Spatial distribution;

[0026] Figure 7 The effect of carrier envelope phase (CEP) on positron trapping; Figure 7 (a) shows the variation of positron energy and radial position with CEP; Figure 7 (b) shows the longitudinal electric field of the laser as a function of phase ψ when CEP is 0, π, and 3π / 2. ' Evolution; Figure 7 (c) represents the relativistic factor as a function of phase ψ when CEP is 0, π, and 3π / 2. ' The evolution of.

[0027] Figure 8The transfer of orbital angular momentum (OAM) between the trapped laser and positrons; where Figure 8 (a) Projection of a typical positron trajectory onto the yz plane; Figure 8 (b) is the distribution of transverse momentum of positrons at t = 50T0; Figure 8 (c) represents the evolution of orbital angular momentum and energy over time; Figure 8 (d) represents the three torques acting on the positron in the x-direction. Evolution over time. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0029] In one embodiment, a positron capture system is provided, comprising:

[0030] A device for capturing light sources and deflecting magnetic fields;

[0031] The trapping light source is used to form a trapping electromagnetic field, which reduces the radial coordinates and radial momentum of the charged particle beam entering the trapping electromagnetic field and confines it to the trapping region; the trapping light source is a left-handed circularly polarized Laguerre Gaussian laser or a vector-polarized beam; there is a π / 2 phase difference between the radial electric field and the longitudinal electric field in the trapping electromagnetic field; the longitudinal electric field includes multiple alternating longitudinal accelerating electric fields and longitudinal decelerating electric fields;

[0032] A magnetic field deflection device is positioned in front of the capture area to separate positrons and electrons in the captured beam of charged particles to obtain a positron beam.

[0033] Because of their opposite electrical charges, they experience opposite forces. The electron's trapping region differs from the positron's trapping region by half a laser cycle. Both electrons and positrons will be trapped and separated. The resulting structure can be viewed as a string of candied hawthorns, for example, the 135th is an electron and the 246th is a positron. After passing through the deflecting magnetic field, the positron and positron will be deflected in different directions to complete the separation.

[0034] In one embodiment, the intensity of the captured light source is I = 1.23 × 10⁻⁶. 21 W / cm 2 The pulse width is τ = 4T0 (half-width), where T0 = 3.34fs, which is the laser period.

[0035] In one embodiment, the system further includes a Gaussian laser source, a concave mirror, and a conversion target.

[0036] The first plane containing the Gaussian laser source and the concave reflector is perpendicular to the second plane containing the concave reflector and the conversion target. The Gaussian laser emitted by the Gaussian laser source is focused and reflected to the conversion target through the concave reflector, causing the conversion target to generate several positive and negative electron pairs and enter the trapping electromagnetic field.

[0037] In one embodiment, the pulse width of the Gaussian laser source is on the picosecond scale, and the intensity of the Gaussian laser source is 1×10⁻⁶. 19 W / cm 2 Magnitude.

[0038] In one embodiment, the conversion target is a high atomic number material; the high atomic number material is a gold target, a lead target, or a copper target.

[0039] like Figure 1 The diagram shown illustrates a positron generation and trapping system. Figure 1 In this study, the capture source was a left-handed circularly polarized Laguerre Gaussian laser.

[0040] like Figure 2 As shown, a positron capture method is provided, comprising:

[0041] Step 202: Turn on the capture light source to form a capture electromagnetic field.

[0042] The capturing light source is a left-handed circularly polarized Laguerre Gaussian laser or a vector-polarized beam. The radial and longitudinal electric fields in the capturing electromagnetic field have a phase difference of π / 2. The longitudinal electric field includes multiple alternating longitudinal accelerating and decelerating electric fields.

[0043] Step 204: By using a radial electric field and multiple alternating longitudinal accelerating and decelerating electric fields, the radial coordinates and radial momentum of the charged particle beam entering the trapping electromagnetic field are reduced and confined to the trapping region.

[0044] A magnetic field deflection device is installed in front of the capture area.

[0045] It is understandable that the charged particle beam entering the trapping electromagnetic field consists of a large number of electron-positron pairs. This scheme mainly focuses on analyzing the motion of the positrons. Taking a left-handed circularly polarized Laguerre Gaussian laser as an example, the radial motion equation of the positron can be written as:

[0046]

[0047] Where p r For radial momentum, E r Let B be the radial electric field, q0 be the elementary charge, and B be the elemental charge. x For the longitudinal magnetic field, v x Longitudinal velocity, Angular magnetic field, Angular velocity.

[0048] Based on the relationship between the electromagnetic fields of left-handed circularly polarized Laguerre-Gaussian lasers, it is easy to see that in most cases... Very small, approximately zero. E r and These two components are close in magnitude and opposite in direction; the radial resultant force is usually proportional to (1-v). x / c)E r . Figure 3 (a) shows the evolution curves of the three radial field components experienced by a typical positron. It can be found that the magnitude and direction of the three components are consistent with the theoretical analysis.

[0049] Taking a left-handed circularly polarized Laguerre-Gaussian laser as an example, when positrons first enter the laser field, due to the weak laser field at the rising edge, the positrons cannot be sufficiently accelerated along the x-axis. The positrons will slide along the rising edge of the envelope to a region with a stronger laser field. They will first slide into the deceleration region (i.e., the longitudinal deceleration electric field) (DZ, E). x <0), and then quickly slide into the next acceleration zone (i.e., the longitudinal acceleration electric field) (AZ, E x >0), because the speed will decrease in DZ, and they will be accelerated and decelerated repeatedly until they slide into a region where the laser field is strong enough and the dephase time is long enough. Where E x This represents the longitudinal electric field. Figure 3 (b) shows the evolution curves of the radial and longitudinal momentum of the positron over time. Figure 3 (c) shows the evolution curves of the radial and co-motion coordinates of the positron over time. For example... Figure 3 (b) and Figure 3 As shown in (c), the positron rapidly slides to x-ct = -1.5 within 7T0. During this process, the longitudinal momentum p x ≈0. Figure 3 (d) shows the radial and longitudinal electric field distributions of a left-handed circularly polarized Laguerre Gaussian laser pulse. E x Areas greater than 0 are marked in gray.

[0050] The expressions for the radial and longitudinal electric fields of the laser are:

[0051]

[0052] Among them, E L0 Let be the peak amplitude of the laser electric field, r be the radial coordinate, and σ0 be the beam waist radius. Let g(x-ct) be the focal spot radius, g(x-ct) be the laser time envelope, and ψ' be the phase of the Laguerreotype laser after removing the azimuth angle.

[0053] According to the expression for the electromagnetic field of the laser used, Er With E x There is a phase difference of π / 2. In the first half of each AZ (from right to left), E r >0, therefore the positron experiences a positive net radial force, and in the latter half of each AZ, E r The value is <0, therefore the net radial force is negative. As the positron slides through each AZ, it experiences half radial acceleration and half radial deceleration. Due to the laser field E... r The force gradually strengthens along the rising edge of the envelope, while the radial momentum gradually decreases after a period of half-acceleration and half-deceleration. More importantly, the duration of the net radial force being positive is much shorter than the duration of its negative value.

[0054] For example, in Figure 3 In (a), the net radial force can remain negative for more than 120T0, while the corresponding radial acceleration phase time is less than 5T0. Accordingly, in Figure 3 In (b), the radial momentum continuously decreases from ~8T0 to ~130T0. Therefore, although the positron is in the first half of AZ p r It increases, but as it slides into the latter half, p r It continues to decrease until it becomes negative. For example... Figure 3 As shown in (b). When p r When <0, the radial position r also decreases, which is why in Figure 3 In (c), r also decreases. For each AZ, the positron has a much higher longitudinal velocity in the latter half than in the first half because it has already been accelerated by half of the AZ; therefore, the positron's phase slip is slower in the latter half of the AZ. In the first half of each deceleration region (DZ, E... x When the velocity of the positron is less than 0, the velocity of the positron is greater than that of the second half, and the net radial force is inward. Therefore, after passing through a DZ, the radial momentum of the positron will further decrease. When the positron slides through an AZ and a DZ, the radial momentum p r Both the radial coordinate r and the radial force q0E decrease significantly. Throughout the process, the radial motion of the positron behaves like a damped oscillation. r and magnetic force These act as restoring force and damping force, respectively. Radial momentum p r The radial coordinate r decreases slowly. Finally, the positron is confined to the trapping region and maintains a small radial momentum, which is the principle of positron trapping in this scheme.

[0055] Step 206: Separate positrons and electrons from the captured charged particle beam using a magnetic field deflection device to obtain a positron beam.

[0056] Because the speed of positrons is much slower than that of laser beams, lasers can quickly "catch up" with and interact with positron beams. Taking a left-handed circularly polarized Laguerre-Gaussian laser as an example, its unique electromagnetic field structure effectively captures and collects positron beams, optimizing their quality. This explanation focuses on positron beams with short pulse lengths; for experimentally longer pulses or positron beams with a certain repetition frequency, long-pulse or high-repetition-rate laser fields will be used for capture.

[0057] A schematic diagram of the positron capture scheme is shown below. Figure 4 As shown, the cylinder represents the positron beam generated by the direct laser-plasma approach, which typically has a large divergence angle and a density of 10⁻⁶. 16 / cm 3 Left and right. The captured laser field used in this scheme is left-handed circularly polarized. A Laguerreotype Gaussian laser of the mode is used, with dimensionless parameters a0 = 30 and a beam waist radius σ0 = 5λ0, where λ0 = 1 μm is the laser wavelength. The pulse width is τ = 4T0, where T0 is the laser period. A positron beam is irradiated with left-handed circularly polarized LG light. Figure 4 The cylindrical portion of the laser (as shown in the image) traps a portion of the positrons within the laser field, compressing them into a positron string. Before the laser's action, the positrons' velocities are anisotropic. After being trapped by the laser, their transverse velocities are suppressed, and their velocity direction shifts forward (the sphere represents the positron's position, and the arrow represents its velocity). After the laser interacts with the positrons, they are effectively trapped. Randomly distributed thermal positrons are transformed into a collimated positron beam, whose radial motion is confined to a smaller range. In the longitudinal direction, the electron beam is compressed into a positron string.

[0058] like Figure 5 As shown, particle simulation results for a left-handed circularly polarized Laguerre Gaussian laser accelerating a positron beam are presented. Among them, Figure 5 (a) shows the density distribution of the positron beam at time 5T0; Figure 5 (b) shows the density distribution of the positron beam at time 50T0; Figure 5 (c) shows the density distribution of the positron beam at time 150T0; Figure 5 (d) represents the evolution of the divergence angle of the positron over time; Figure 5 (e) shows the evolution of the positron energy spectrum over time. It can be seen that the positrons are compressed longitudinally, forming positron pulse chains, each with a thickness of less than 1 fs. Simultaneously, from... Figure 5As can be seen in (b) and (c), the positron beam is confined laterally to a very small area, approximately r < 6λ0. Therefore, the positron density can be effectively increased. At 50T0, the maximum positron density is approximately 70 times the initial density. If a longer target is used, the positron beam can be compressed to even higher densities. Experimental positron beams typically have picosecond (ps) lengths, thus allowing for extremely high compression. Figure 5 As can be seen from (d), the divergence angle of the positron decreases sharply with time. At t = 150T0, the peak divergence angle is only 1.1° and the full width at half maximum (FWHM) is only 2.84°. Figure 5 (e) shows that the energy of the positron increases significantly over time, reaching a maximum energy of approximately 450 MeV at t = 150T0, which is two orders of magnitude higher than the initial energy. With a more powerful laser, the positron energy could be even higher.

[0059] Table 1 shows the evolution of the positron capture rate over time for lasers with a0 = 30 and a0 = 10. Here, the capture rate is defined as the positron capture rate at... The ratio of the number of positrons trapped within the laser beam to the number of positrons initially located within the laser focal spot (r0<σ).

[0060] Table 1 shows the evolution of the positron capture rate over time for lasers with a0 = 30 and a0 = 10.

[0061]

[0062] Table 1 shows the evolution of positron capture efficiency over time at different laser intensities a0. For a laser with a0 = 10, the initial capture efficiency is as high as 35%, but it decreases rapidly over time, reaching only about 17% at 50T0. The laser intensity must be increased to accommodate the positron temperature of MeV. When the laser intensity is increased to a0 = 30, the initial capture efficiency exceeds 40%. Even at 150T0, close to 30% of positrons are captured. By increasing the laser intensity, even positron beams at higher temperatures can be effectively captured.

[0063] Figure 6 (a) shows the normalized probability density of positrons trapped at different initial radial positions r0. It can be seen that the trapping probability density decreases relatively slowly with r0. Even at the beam waist radius (σ0=5λ0), the trapping probability density is still 70% of the maximum value. This indicates that for a laser with a certain focal spot radius, our scheme can trap positrons over a larger range. Figure 6 (b) When the value is 100T0, the captured positrons are in (η x ,η ⊥ The spatial distribution of η x η represents the energy that a positron gains from a longitudinal electric field, while η represents the energy that a positron gains from a longitudinal electric field. ⊥This represents the energy gained from the transverse electric field. From this, we can clarify whether the longitudinal or transverse electric field dominates during the acceleration of positrons. It can be seen that for most positrons, the energy gain from the transverse electric field is small. Approximately 75% of the tracked electrons have an energy gain in (-50 < η). ⊥ <50, -100<η x Within the region <450°, this indicates that the longitudinal electric field dominates the acceleration process for most trapped electrons. Therefore, when studying the trapping mechanism, we primarily investigate the acceleration by the longitudinal electric field.

[0064] Our method can not only obtain high-energy positrons, but also adjust the positron energy by changing the laser parameters. Figure 7 The effect of carrier envelope phase (CEP) on positron capture. Figure 7 (a) shows the variation of positron energy and radial position with CEP, where γ is the relativistic factor proportional to the positron energy, and r max The maximum radial position during the motion is used to measure whether the positron is effectively captured; Figure 7 (b) shows the longitudinal electric field of the laser as a function of phase ψ when CEP is 0, π, and 3π / 2. ' Evolution; Figure 7 (c) represents the relativistic factor as a function of phase ψ when CEP is 0, π, and 3π / 2. ' The evolution of.

[0065] It can be seen that as the carrier envelope phase changes, r max The variation is relatively small, basically within 6λ0, meaning that positrons can always be effectively captured regardless of changes in the carrier envelope phase. We can also observe that γ varies between 0 and 230 as the carrier envelope phase changes, indicating that the energy for capturing positrons can be effectively adjusted by regulating the carrier envelope phase. Figure 7 (b) and Figure 7 (c) The reason for the positron energy regulation was analyzed, namely that the change in the carrier envelope phase can change the magnitude of the longitudinal electric field that actually accelerates the positron, thereby regulating the positron energy.

[0066] In this scheme, the positron can gain orbital angular momentum from the trapping field. Figure 8 The transfer of orbital angular momentum (OAM) between the trapped laser and positrons; where Figure 8 (a) Projection of a typical positron trajectory onto the yz plane; Figure 8 (b) is the distribution of transverse momentum of positrons at t = 50T0; Figure 8 (c) represents the orbital angular momentum L x And the evolution of energy γ over time; Figure 8 (d) represents the torque M experienced by the positron in the x-direction.x and resultant torque M n,x As time goes by, among them It refers to M x The three components. For example... Figure 8 (a) and Figure 8 As shown in (b), the positron rotates counterclockwise in the yz plane most of the time. Furthermore, the trend of the positron's orbital angular momentum is remarkably similar to that of its energy, such as... Figure 8 As shown in (c). In our scheme, due to the effect of the laser electromagnetic field, the angular motion of the positron is subjected to three torque components. The influence of the electric field. By tracking the above three components, we found that the net torque that causes the positron to rotate counterclockwise is always proportional to the angular electric field. Since the change of the angular electric field component with time is similar to that of the accelerating electric field, the change of orbital angular momentum is also very similar to the change of energy (denoted by γ).

[0067] In summary, this scheme uses a laser with a special structure as a capture field to capture charged particles and optimize their quality. Traditionally, magnetic fields generated by coil structures are mostly used to capture charged particles. Compared with traditional schemes, this scheme has many advantages, such as not only capturing charged particles but also reducing their divergence angle, allowing them to continue transmitting stably after leaving the capture field.

[0068] Besides using a left-handed circularly polarized Laguerre Gaussian laser, other vector-polarized beams, such as radially polarized light, can also achieve similar effects in capturing laser fields, but the results will be slightly different.

[0069] Vector-polarized light comes in many forms, such as radially polarized light and angularly polarized light. Here, we take radially polarized light as an example. The radial motion equation of a positron under the influence of radially polarized light is:

[0070]

[0071] This equation has fewer features compared to the radial motion equation for left-handed circularly polarized Laguerre Gaussian light. This item, due to Typically much smaller than the speed of light, this factor was neglected in the previous analysis; therefore, the resultant force is proportional to the radial electric field E. r The conclusion will not change. The E of vector-polarized light x E r The expression is exactly the same as that of a left-handed circularly polarized Laguerre Gaussian laser, therefore the acceleration and collimation mechanisms are identical. The difference is that radially polarized light does not have... B xThese two components do not involve the transfer of orbital angular momentum. In practical applications, different trapping laser fields can be selected as needed. If positrons with orbital angular momentum are required, a Laguerre Gaussian laser is used; if orbital angular momentum is not required, radially polarized light is used.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positron capture system, characterized in that, The system includes: A device for capturing light sources and deflecting magnetic fields; The capturing light source is used to form a capturing electromagnetic field, which reduces the radial coordinates and radial momentum of the charged particle beam entering the capturing electromagnetic field and confines it to the capturing region; the capturing light source is a left-handed circularly polarized Laguerre Gaussian laser or a vector-polarized beam; there is a π / 2 phase difference between the radial electric field and the longitudinal electric field in the capturing electromagnetic field; the longitudinal electric field includes multiple alternating longitudinal accelerating electric fields and longitudinal decelerating electric fields; The magnetic field deflection device is positioned in front of the capture region to separate positrons and electrons in the captured charged particle beam to obtain a positron beam.

2. The system according to claim 1, characterized in that, The intensity of the captured light source is ; pulse width is ,in This refers to the laser cycle.

3. The system according to claim 1, characterized in that, The system also includes: Gaussian laser source, concave mirror, and conversion target; The first plane containing the Gaussian laser source and the concave mirror is perpendicular to the second plane containing the concave mirror and the conversion target. The Gaussian laser emitted by the Gaussian laser source is focused and reflected to the conversion target by the concave reflector, causing the conversion target to generate several positive and negative electron pairs and enter the trapping electromagnetic field.

4. The system according to claim 3, characterized in that, The pulse width of the Gaussian laser source is on the picosecond scale; the intensity of the Gaussian laser source is... Magnitude.

5. The system according to claim 3, characterized in that, The conversion target is a high atomic number material; the high atomic number material is a gold target, a lead target, or a copper target.

6. A positron capture method, characterized in that, The method includes: A trapping light source is activated to form a trapping electromagnetic field; the trapping light source is a left-handed circularly polarized Laguerre Gaussian laser or a vector-polarized beam; the radial electric field and the longitudinal electric field in the trapping electromagnetic field have a phase difference of π / 2; the longitudinal electric field includes multiple alternating longitudinal accelerating electric fields and longitudinal decelerating electric fields; The radial electric field and multiple alternating longitudinal accelerating and decelerating electric fields reduce the radial coordinates and radial momentum of the charged particle beam entering the capturing electromagnetic field and confine it to the capturing region; a magnetic field deflection device is provided in front of the capturing region. The positrons and electrons in the captured charged particle beam are separated by the magnetic field deflection device to obtain a positron beam.

7. The method according to claim 6, characterized in that, The intensity of the captured light source is ; pulse width is ,in This refers to the laser cycle.

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