A method for generating a pulsed neutron source based on dual-beam laser-driven ultra-thin targets

Abstract

The present application relates to a method for generating a pulsed neutron source based on a dual-beam laser-driven ultra-thin target. The method comprises: setting an ultra-thin target in the center of a pulsed neutron source device, and simultaneously vertically incident two laser beams from the left and right boundaries of the pulsed neutron source device to generate a laser neutron source; by changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons generated by the laser neutron source is manipulated, and directional emission of neutrons is achieved. The present invention greatly broadens the use scenarios and application potential of the generated pulsed neutron source.

Description

Technical Field

[0001] The present application relates to the technical field of pulsed neutron sources, and in particular to a method for generating a pulsed neutron source based on dual-beam opposing laser-driven ultra-thin targets. Background Art

[0002] Neutron sources have important application value in the fields of neutron activation analysis, neutron photography and isotope production. However, although the neutron sources based on traditional accelerators and fission reactors have high yield and large flux, they have problems such as large device size, high cost, complex environmental radiation and long neutron source pulse width. In view of the needs of practical applications, people are eager to obtain pulsed neutron sources with small size, low cost, controllable and no accompanying radiation hazards. Summary of the invention

[0003] Based on this, it is necessary to provide a method for generating a pulsed neutron source based on a dual-beam opposed laser-driven ultra-thin target that can have a wider application scenario in order to address the above technical problems.

[0004] A method for generating a pulsed neutron source based on dual-beam opposing laser driving an ultra-thin target, the method comprising:

[0005] An ultra-thin target is arranged in the center of the pulsed neutron source device, and two laser beams are incident vertically from the left and right boundaries of the pulsed neutron source device at the same time to generate a laser neutron source;

[0006] By changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons produced by the laser neutron source is manipulated, and the directional emission of neutrons is achieved.

[0007] In one of the embodiments, it also includes: simulating the process of generating a laser neutron source by driving an ultra-thin target with dual-beam opposing lasers through a neutron post-processing module based on the Monte Carlo method, and analyzing the neutron energy, angular distribution, pulse width, volume generation rate, generation rate and neutron yield information of the neutrons generated by the laser neutron source.

[0008] In one of the embodiments, the laser is also circularly polarized laser.

[0009] In one of the embodiments, the method further includes: when the rotation direction of the electric field vector of the left-side incident circularly polarized laser is set to be right-handed and the rotation direction of the electric field vector of the right-side incident circularly polarized laser is set to be left-handed, or the rotation direction of the electric field vector of the left-side incident circularly polarized laser is set to be right-handed and the rotation direction of the electric field vector of the right-side incident circularly polarized laser is set to be right-handed, the relative phase difference of the two circularly polarized laser beams is set to 0, so that the neutron yield of neutrons generated by the laser neutron source is maximized.

[0010] In one of the embodiments, it also includes: when the rotation direction of the electric field vector of the left-side incident circularly polarized laser is set to be right-handed and the rotation direction of the electric field vector of the right-side incident circularly polarized laser is set to be right-handed, the relative phase difference between the two circularly polarized laser beams is set to be 0.5π or 1.5π, so that the neutrons generated by the laser neutron source have better angular distribution and forward directionality.

[0011] In one of the embodiments, it also includes: setting an ultra-thin target in the center of the pulsed neutron source device, and simultaneously and vertically incident two laser beams from the left and right boundaries of the pulsed neutron source device to generate a laser neutron source; the pulse width of the laser neutron source can reach 23.1fs.

[0012] The above-mentioned method for generating a pulsed neutron source based on a dual-beam laser-driven ultra-thin target is to generate a laser neutron source by setting an ultra-thin target in the center of the pulsed neutron source device and simultaneously vertically incident two laser beams from the left and right boundaries of the pulsed neutron source device; by changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons generated by the laser neutron source is manipulated and the directional emission of neutrons is achieved. The present invention greatly broadens the use scenarios and application potential of the generated pulsed neutron source. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic flow chart of a method for generating a pulsed neutron source based on dual-beam opposing lasers driving an ultra-thin target in one embodiment;

[0014] Figure 2 A schematic diagram of generating neutrons by interaction between dual-beam opposing lasers and an ultra-thin target in one embodiment;

[0015] Figure 3 A schematic diagram of circularly polarized dual laser beams with different electric field vector rotation directions and initial relative phase differences irradiated from left and right sides in one embodiment;

[0016] Figure 4 is a flow chart of a neutron post-processing module based on the Monte Carlo method in one embodiment;

[0017] Figure 5 2 is a neutron energy spectrum diagram under different physical parameters in another embodiment, wherein (a) is a neutron energy spectrum diagram under different physical parameters in the RCP+LCP case, and (b) is a neutron energy spectrum diagram under different physical parameters in the RCP+RCP case;

[0018] Figure 6 2 is a neutron angle distribution diagram under different physical parameters at time t=25T0 in another embodiment, wherein (a) is a neutron angle distribution diagram under different physical parameters in the RCP+LCP case, and (b) is a neutron angle distribution diagram under different physical parameters in the RCP+RCP case;

[0019] Figure 7 is a graph showing the relationship between the neutron production rates of different physical parameters and time in another embodiment, wherein (a) is a graph showing the relationship between the neutron production rates of different physical parameters and time in the RCP+LCP case, and (b) is a graph showing the relationship between the neutron production rates of different physical parameters and time in the RCP+RCP case;

[0020] Figure 8 In another embodiment, different 51 Under the condition, the spatial distribution diagram of neutron production rate under different situations at time t=32T0, where (a)-(d) are the spatial distribution diagrams of neutron production rate under the RCP+LCP situation, and (e)-(h) are the spatial distribution diagrams of neutron production rate under the RCP+RCP situation;

[0021] Fig. 9 1 is a graph showing the variation of neutron yield of different physical parameters over time in another embodiment, wherein (a) is a graph showing the variation of neutron yield of different physical parameters over time in the RCP+LCP case, and (b) is a graph showing the variation of neutron yield of different physical parameters over time in the RCP+RCP case;

[0022] Fig.10 In another embodiment, different 51 Under the conditions, the spatial distribution diagram of neutron production rate under different situations at t=50T0, where (a)-(d) are the spatial distribution diagrams of neutron production rate under RCP+LCP situation, and (e)-(h) are the spatial distribution diagrams of neutron production rate under RCP+RCP situation. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] In one embodiment, Figure 1 As shown, a method for generating a pulsed neutron source based on a dual-beam opposing laser driving an ultra-thin target is provided, comprising the following steps:

[0025] Step 102, an ultra-thin target is arranged in the center of the pulsed neutron source device, and two laser beams are incident vertically from the left and right boundaries of the pulsed neutron source device simultaneously to generate a laser neutron source.

[0026] like Figure 2 The figure shows a schematic diagram of the interaction between the dual-beam laser beam and the ultra-thin target to produce neutrons. In this embodiment, the laser is a circularly polarized laser, and the ultra-thin target is a deuterium target. When the dual-beam circularly polarized laser beam interacts with the deuterium target, the deuterium ions undergo a DD fusion reaction during the compression process, thereby producing neutrons.

[0027] Step 104, by changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons generated by the laser neutron source is manipulated, and the directional emission of neutrons is achieved.

[0028] The present invention considers the initial relative phase difference (IRPD, variable φ) of the two laser beams. 51 ) and the influence of the rotation direction of the electric field vector of the circularly polarized laser on the interaction process, the process of generating a laser neutron source by driving an ultra-thin target with dual-beam opposed lasers is simulated by a neutron post-processing module based on the Monte Carlo method, and the neutron energy, angular distribution, pulse width, volume generation rate, generation rate and neutron yield information of the neutrons generated by the laser neutron source are analyzed. It is found that the neutron yield of the neutrons generated by the laser neutron source can be manipulated by changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, and the directional emission of neutrons can be achieved.

[0029] The electric field vector rotation direction includes left-handed (LCP) and right-handed (RCP). Circularly polarized lasers are classified into two groups, as shown in Table 1.

[0030] Left side incident laser Right side incident laser <![CDATA[φ 51 ]]> <![CDATA[φ 51 ]]> <![CDATA[φ 51 ]]> <![CDATA[φ 51 ]]> RCP LCP 0 π / 2 <![CDATA[ π ]]> 3π / 2 RCP RCP 0 π / 2 <![CDATA[ π ]]> 3π / 2

[0031] Table 1 Classification of circularly polarized laser variables

[0032] Figure 3 A schematic diagram of two circularly polarized laser beams with different electric field vector rotation directions and initial relative phase differences irradiated from the left and right sides is given. The two coordinate axes represent the starting position coordinates of the two laser beams, which correspond to the two boundary interfaces of the simulation box.

[0033] In order to be consistent with the coordinate system rules of the EPOCH program, the laser propagation direction is defined as the x-axis, the vertical upward direction is defined as the y-axis, and the z-axis is determined by the right-hand screw rule. 51 , fix the initial phase angle of the incident laser on the left side to 0 degrees, that is, the direction of the electric field vector at the initial moment is consistent with the positive direction of the z-axis, and change the direction of the initial electric vector of the incident laser on the right side so that the electric vector directions of the two laser beams have an angle φ 51 It should be noted that for the RCP+LCP case, φ 51 It remains fixed during laser propagation, but for the RCP+RCP case, φ 51 It will change periodically during the propagation process.

[0034] The analysis found that under the RCP+LCP and RCP+RCP situations, φ 51= 0 corresponds to the highest neutron yield; in addition, the spatial distribution of neutron body yield was observed, and it was found that the dual-beam opposing laser can effectively control the neutron sources with different requirements to produce neutrons, especially in terms of angular distribution and forwardness. 51 =0.5π) and (RCP+RCP,φ 51 =1.5π) will bring about a very ideal effect, that is, the directional emission of neutrons can be achieved.

[0035] In the above-mentioned pulse neutron source generation method based on dual-beam laser-driven ultra-thin target, an ultra-thin target is set in the center of the pulse neutron source device, and two laser beams are simultaneously incident vertically from the left and right boundaries of the pulse neutron source device to generate a laser neutron source; by changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons generated by the laser neutron source is manipulated, and the directional emission of neutrons is achieved. The present invention greatly broadens the use scenarios and application potential of the generated pulse neutron source.

[0036] In one embodiment, a neutron post-processing module based on the Monte Carlo method is used to simulate the process of generating a laser neutron source by driving an ultra-thin target with dual-beam opposing lasers. The flow chart of the neutron post-processing module based on the Monte Carlo method is as follows: Figure 4 shown.

[0037] Two laser beams were incident vertically from the left and right boundaries of the simulation area at the same time, and the length of the simulation box was set to 36μm and the height to 24μm. In the one-dimensional simulation environment, the spatial resolution used in the x-direction was 0.0002μm, while in the two-dimensional simulation stage, the spatial resolution in both the x-direction and the y-direction was 0.002μm, and other parameters remained the same.

[0038] The deuterium solid target is located in the center of the simulation box. The distance between the front surface of the solid target and the left boundary of the simulation space region is d1 = 17.95 μm. The thickness of the ultra-thin target is d = 0.1 μm, and the height is h = 24 μm, which is consistent with the height of the simulation box. The solid target is composed of deuterium ions and electrons, and the number density of deuterium ions and electrons is 50n c , where n c =1.1×10 27 m -3 is the critical density of plasma corresponding to the laser wavelength λ0 = 1 μm. Grid resolution, 50 deuterium ions and 50 electrons are placed in each grid. For circularly polarized lasers, the intensities of the two laser beams are The normalized amplitude E0 is the maximum electric field amplitude of the laser, e and m e are the electron charge and mass, c is the speed of laser light in vacuum. Laser focal spot radius σ L=6μm, pulse width τ L =10T0, where T0 = 3.3fs is the laser period.

[0039] The PIC program is used to obtain the position and velocity information of deuterium ions. The deuterium ions are assigned to different grids according to their positions. The deuterium ions in each grid are randomly sampled, and the ions are paired to calculate the information of neutrons produced by each pair of ions. By consulting the literature, D(d,n) is obtained. 3 The differential cross section dσ / dΩ data of He reaction. n The energy of the emitted neutron can be expressed as:

[0040]

[0041] Where η=(M n +M He )(M He -M D +M He Q / ε r ) / M D M n , Q = 3.266 MeV is the reaction energy of the reaction, M n and M He are the mass of the neutron and the mass of the helium nucleus; ε r =m r v 2 / 2 is the mass energy of the collision center (m r =m D m D / (m D +m D )=m D / 2 is the reduced mass), and is the ion velocity information output by the PIC program, is the relative velocity of the two colliding ions. Substituting the known parameters, equation (1) can be simplified as:

[0042]

[0043] By interpolating the differential reaction cross section, each collision energy ε can be obtained n The mapping relationship with the differential cross section can be calculated by σ = ∫ (dσ / dΩ) dΩ to obtain the total reaction cross section. The neutron production rate corresponding to each grid is Then integrate the grid volume to get the neutron production rate P n =∫R n dV, neutron yield can also be calculated by N n =∫P nTherefore, according to formula (2) and the data of differential cross section, the volume production rate of neutrons R can be calculated: n , neutron production rate P n And the output N n , and the energy and angular distribution of neutrons can also be obtained.

[0044] Figure 5 It is the different neutron energy spectra under different relative phase angles and laser rotation directions. Through parameter scanning, it can be clearly observed that φ 51 = 0 produces significantly higher neutron energy than other parameters, with the maximum neutron energy reaching 13.2 MeV, and is also the most ideal in terms of high-energy neutron number density. At the same time, for the RCP+RCP case, different relative phase differences can reflect the characteristic peaks of the energy spectrum.

[0045] The angular distribution of neutrons is an important parameter for judging and measuring the quality of neutron sources. The angular distribution characteristics of neutrons produced by DD reactions can be diagnosed by using differential reaction cross sections. Figure 6 This is the angular distribution of neutron generation corresponding to the 25th laser cycle. It can be observed that under different parameters, the forward property of the angular distribution of neutron generation is relatively ideal. Therefore, it can be preliminarily determined that the influence of the two types of physical parameters on the angular distribution is not significant.

[0046] The pulse width of the neutron source is τ n It is one of the important physical parameters. Neutron sources with different pulse widths have different application values. Figure 7 It is the relationship between the neutron reaction rate and time under different circumstances. The present invention can achieve a pulse width of about 23.1fs, which brings many new application scenarios and huge potential to the laser neutron source. Compared with other neutron sources, the laser neutron source produced by this method has great advantages in pulse width. The pulse width of the neutron source in the prior art is generally in the order of ps. The present invention uses the mechanism of interaction between ultra-thin targets and counter-radiation to obtain a neutron source with a shorter pulse width. Through this method, we obtain a femtosecond pulse neutron source, which is about 50 times shorter than the pulse width produced by a general neutron source. This makes the neutron source produced by this method have more application scenarios, such as important applications such as neutron cancer treatment.

[0047] Figure 8 This is a two-dimensional pseudo-color image based on the neutron production rate at t = 32T0. Since the neutron production rate inside the simulation box varies greatly, in order to more intuitively display the spatial distribution of the neutron production rate, the simulation results are processed logarithmically to obtain the results shown in the image. First, analyze Figure 8 (a)-(d) corresponding to the RCP+LCP case: Observe φ 51=0.5π and φ 51 =1.5π, it can be found that the neutron production rate inside the expanded solid target is higher than that outside. At the same time, because the neutrons move under the joint action of the two laser beams, this also provides support for the forward nature of the neutrons. 51 =π, it can be found that neutrons are basically stably generated at the deuterium target position. For the RCP+RCP case, the neutron generation rate is generated near the solid target and at φ 51 When =0, the generation rate is the highest.

[0048] Neutron yield is an important parameter for evaluating the quality of neutron sources, so it is necessary to study neutron yield. Fig. 9 (a) Given the RCP+LCP case, the maximum neutron yield is φ 51 =0 corresponds to 9.1×10 4 , for φ 51 =π, the existence of a steady-state solution causes the deuterium ion to be incomparable with other parameters in terms of temperature, and φ 51 =0.5π and φ 51 =1.5π, the final output is the same, which also verifies the correctness of the post-processing module. Fig. 9 (b) Given the RCP+RCP case, it is found that φ 51 =0, the maximum neutron yield reached 1.37×10 5 , which is much higher than any other physical parameter. At the same time, through simulation, it is found that the spatial distribution of neutrons in this case is also the most extensive.

[0049] For RCP+LCP Fig.10 (a)-(d), the most noteworthy one is φ 51 =0.5π and φ 51 =1.5π, we can see that this type of laser neutron source exhibits good angular distribution and forwardness, which are important parameters for evaluating the quality of neutron sources. At the same time, the neutron yields corresponding to these two parameters are also relatively ideal, which provides a new idea for laser manipulation of neutron angular distribution. 51 = 0, the spatial distribution of neutron yield is mainly caused by instability, but this also makes the angular distribution of neutron sources less than ideal; for φ 51 =π, due to the existence of a steady-state solution, the neutron yield and spatial distribution have certain disadvantages compared with the other three sets of parameters.

[0050] observe Fig.10 (e)-(f), we can first see the φ with the largest output 51 =0 shows the strongest distribution characteristics, and a periodic neutron spatial distribution appears along the central axis; φ 51=0.5π and φ 51 =1.5π, a nearly parallel neutron beam appeared in the spatial distribution, and a sawtooth periodic arrangement was shown in the central area of ​​the neutron source; when φ 51 =π, the neutron source does not have obvious forward characteristics and is not very outstanding in terms of yield.

[0051] This embodiment proposes a six-dimensional evaluation mechanism to evaluate the quality of laser neutron sources. Different laser neutron source devices are evaluated based on information such as neutron yield, neutron energy, neutron angular distribution, neutron production rate, neutron body production rate, pulse width, etc., so that they can be combined with practical applications and better integrate laser neutron sources with practical applications.

[0052] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0053] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, 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.

[0054] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for generating a pulsed neutron source based on dual-beam opposing laser driving an ultra-thin target, characterized in that: The method comprises: An ultra-thin target is arranged in the center of the pulsed neutron source device, and two laser beams are incident vertically from the left and right boundaries of the pulsed neutron source device at the same time to generate a laser neutron source; By changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons produced by the laser neutron source is manipulated, and the directional emission of neutrons is achieved.

2. The method according to claim 1, characterized in that The method further comprises: The process of generating a laser neutron source by driving an ultra-thin target with dual-beam opposing lasers is simulated by a neutron post-processing module based on the Monte Carlo method, and the neutron energy, angular distribution, pulse width, volume generation rate, generation rate and neutron yield information of the neutrons generated by the laser neutron source are analyzed.

3. The method according to claim 1, characterized in that The laser is circularly polarized laser.

4. The method according to claim 3, characterized in that By changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the neutron yield of the neutrons generated by the laser neutron source is manipulated, including: When the rotation direction of the electric field vector of the left-side incident circularly polarized laser is set to be right-handed and the rotation direction of the electric field vector of the right-side incident circularly polarized laser is set to be left-handed, or the rotation direction of the electric field vector of the left-side incident circularly polarized laser is right-handed and the rotation direction of the electric field vector of the right-side incident circularly polarized laser is right-handed, the relative phase difference of the two circularly polarized laser beams is set to 0, so that the neutron yield of neutrons generated by the laser neutron source is maximized.

5. The method according to claim 3, characterized in that: By changing the rotation direction and relative phase difference of the electric field vectors of the two laser beams, the directional emission of neutrons is achieved, including: When the rotation direction of the electric field vector of the left-side incident circularly polarized laser is set to be right-handed and the rotation direction of the electric field vector of the right-side incident circularly polarized laser is set to be right-handed, the relative phase difference between the two circularly polarized laser beams is set to be 0.5π or 1.5π, so that the neutrons generated by the laser neutron source have better angular distribution and forwardness.

6. The method according to claim 1, characterized in that An ultra-thin target is arranged in the center of a pulsed neutron source device, and two laser beams are incident vertically from the left and right boundaries of the pulsed neutron source device at the same time to generate a laser neutron source, including: An ultra-thin target is arranged in the center of the pulsed neutron source device, and two laser beams are incident vertically from the left and right boundaries of the pulsed neutron source device at the same time to generate a laser neutron source; the pulse width of the laser neutron source can reach 23.1fs.

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