Converter for laser beam target neutron source and its optimization design method

Abstract

The present invention relates to the technical field of converter design for laser beam target neutron sources, and provides a converter for a laser beam target neutron source and an optimized design method therefor. The converter for a laser beam target neutron source includes a front plate, surrounding side plates, and a rear plate. The front plate, the surrounding side plates, and the rear plate enclose to form a sealed inner cavity, and the sealed inner cavity is filled with inclusions to form a wrapped cube structure; at least one of the front plate, the surrounding side plates, and the rear plate is made of a material with stable chemical properties, good mechanical properties, and easy to form; the inclusions are filled with substances with excellent neutron generation ability. By designing a wrapping layer to wrap the beryllium material without affecting the neutron generation ability of beryllium, the experimental safety is provided while ensuring the stability of the neutron yield, so as to solve the technical problem that the existing converter limits the popularization of the laser beam target neutron source in high-precision applications.

Description

Technical Field

[0001] The present invention relates to the technical field of the design of converters for laser beam target neutron sources, and in particular to a converter for a laser beam target neutron source and an optimized design method therefor. Background Art

[0002] Neutrons have important application values in the fields of neutron radiography, neutron activation analysis, neutron cancer treatment, production of radioactive isotopes, and material research. Neutrons can be classified into different types according to energy, such as cold neutrons, thermal neutrons, resonance neutrons, slow neutrons, intermediate-energy neutrons, fast neutrons, and relativistic neutrons. Different application fields have different requirements for neutron energy. There are no free neutrons in nature. A device that releases the "bound state" neutrons existing in the atomic nucleus from the nucleus through artificial methods is called a neutron source. Neutron sources can be divided into continuous neutron sources and pulsed neutron sources. Compared with continuous neutron sources, pulsed neutron sources have advantages such as short pulse width and high flux (including peak flux and average flux), and have important applications in fast neutron resonance imaging, laboratory astrophysics research, etc. At present, the spallation neutron source is a most typical pulsed neutron source, which has advantages such as high yield, short pulse width (in the order of nanoseconds or microseconds), easy control and regulation, wide energy range, and low γ background, and is the neutron source with the most obvious advantages among all traditional neutron sources. However, the spallation neutron source device is relatively large in size and high in cost. In recent years, in order to meet the application requirements, pulsed neutron sources have mainly developed in the directions of high flux, short pulse width, full energy range, miniaturization, and low cost.

[0003] The chirped pulse amplification technology has continuously promoted the development of ultra-intense and ultra-short lasers. Ultra-intense and ultra-short lasers can accelerate charged particles to hundreds of megaelectron volts (MeV) within a time scale of picoseconds (ps) or even femtoseconds (fs) and a spatial scale of micrometers (μm). Laser acceleration is an important way to realize the miniaturization of particle accelerators, and also provides a good opportunity for the development of new neutron sources. Laser neutron sources use the interaction between intense lasers and matter to generate electromagnetic radiation or high-energy particles, and then induce different nuclear reactions to generate neutrons, and have characteristics such as microfocus, short pulse width, and high flux. Laser neutron sources can be divided into cluster neutron sources, fusion neutron sources, photonuclear neutron sources, and beam target neutron sources according to the neutron generation method. From the perspectives of neutron yield, forwardness, and device compactness, the beam target neutron source is the best way for laser-driven tabletop high-flux pulsed neutron sources. At present, forward neutrons with a yield exceeding 10 10 n / sr can be generated experimentally.

[0004] However, existing laser beam target neutron sources still have deficiencies in aspects such as neutron yield, divergence angle control, and device compactness, which limit their popularization in high-precision applications. In particular, the design of the converter plays a key role in the neutron generation efficiency and directivity, but there is currently a lack of systematic optimization methods. Summary of the Invention

[0005] The present invention provides a converter for a laser beam target neutron source and an optimization design method thereof. Since pure beryllium material with high neutron generation capacity is in powder form and highly toxic, it will contaminate a target chamber during the experiment, which is very unfavorable for conducting laser beam target neutron source experiments. By designing a wrapping layer to wrap the beryllium material without affecting the neutron generation capacity of the beryllium, the experimental safety is provided while ensuring the stability of the neutron yield, so as to solve the technical problem that the existing converter limits the promotion of the laser beam target neutron source in high-precision applications.

[0006] The present invention provides a converter for a laser beam target neutron source, comprising a front plate, surrounding side plates and a rear plate, wherein the front plate, surrounding side plates and the rear plate are enclosed to form a sealed inner cavity, and the sealed inner cavity is filled with embedded objects to form a wrapped cubic structure; at least one of the front plate, the surrounding side plates and the rear plate is made of a material with stable chemical properties, good mechanical properties and easy molding; and the embedded objects are filled with a material with excellent neutron generating ability.

[0007] Further, at least one of the front plate, the surrounding side plates and the rear plate is made of LiH, LiF or LiD.

[0008] Furthermore, the embedded material adopts beryllium powder.

[0009] Furthermore, the thickness of the front plate and / or the rear plate is 0.1 cm to 0.6 cm.

[0010] Furthermore, the height of the surrounding side panels in the front-rear direction is 1 cm to 8 cm; the thickness of the surrounding side panels is 0.1 cm to 0.5 cm.

[0011] Furthermore, the side length of the front plate and / or the rear plate and / or the surrounding side plates is 3 cm to 10 cm.

[0012] Furthermore, at least one of the front plate, the rear plate and the surrounding side plates is a lithium hydride ceramic plate prepared by warm isostatic pressing.

[0013] Furthermore, the front panel and the surrounding side panels and / or the surrounding side panels and the rear panel are sealed and connected by using high-adhesion glue.

[0014] An optimized design method for a converter of a laser beam target neutron source is also provided, including the following steps: S100. Select two converter structures. The first one is a cube structure made of a single material, and the second one is a wrapped cube structure; S200. Carry out numerical simulations by comprehensively using the radiation hydrodynamics code FLASH, the particle simulation code EPOCH, and the Monte Carlo code Geant4; S300. Focus on the typical parameter indicators of the output light of a multi-petawatt femtosecond laser device. Considering the laser prepulse and the post-target contamination layer, obtain the quality characteristics of intense ion beams driven by lasers with different intensities, and then obtain the influence law of the material, geometric shape, and position of the converter structure on the quality of the beam target neutron source, and further improve the optimized design scheme of the converter to improve the neutron yield and the ratio of the forward-side to lateral neutron yields.

[0015] Furthermore, analyze the cube structure and the wrapped cube structure separately; the length and width of the converter structure are both 4 cm, the thickness of the converter structure is designed to be 5 cm, and the distance between the converter structure and the throw target is set to 1 cm; the material of the cube structure is selected from LiH, LiF, LiD, or Be, and the converter is a single material component; the outer material of the wrapped cube structure is selected from LiH, LiF, or LiD, and the embedded material is selected from Be; based on the simulation results of neutrons generated by the interaction of ion beams driven by lasers with different intensities with different converter structures, the neutron generation ability is obtained.

[0016] The present invention has the following beneficial effects:

[0017] The converter for the laser beam target neutron source of the present invention seals and wraps the inlay with strong neutron generation ability but high toxicity (such as pure beryllium material, beryllium powder) by designing a wrapping layer, effectively preventing the leakage and diffusion of the highly toxic inlay during the experiment, avoiding the pollution of the target chamber, and thus significantly improving the safety of the experiment; the inlay is filled with a substance with excellent neutron generation ability (such as beryllium). On the premise of not affecting its neutron generation ability, the wrapping structure ensures the stability and efficiency of the neutron source; the wrapped cube structure can restrict the divergence angle of neutrons, improve the collimation of the neutron beam, and thus enhance the forwardness of the neutron source, which is of great significance for applications requiring highly directional neutron beams (such as neutron radiography and material analysis); combined with the optimized design, the converter structure of the present invention helps to reduce the neutron pulse width, thereby improving the energy resolution of the neutron source and making it more suitable for high-precision applications such as fast neutron resonance imaging; the design of the converter of the present invention realizes the miniaturization and compactness of the converter by optimizing the material selection and structure layout, which is beneficial to the overall miniaturization and low-cost goal of the laser beam target neutron source; by adjusting the composition and structure of the inlay, the converter can adapt to different neutron energy requirements and meet various applications from fast neutrons to thermal neutrons. The converter for the laser beam target neutron source of the present invention and its optimized design method not only improve the safety of the experiment and the performance of the neutron source, but also provide technical support for the popularization of the laser beam target neutron source in high-precision applications.

[0018] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The present invention will be further described in detail below with reference to the drawings. Brief Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0020] Figure 1 Schematic diagram of the numerical simulation study for the embodiment of the present invention;

[0021] Figure 2 Results of ablation of the solid target by different-intensity laser prepulses (spatial distribution of electron density) for the embodiment of the present invention, where Figure 2 (a), Figure 2 (b), Figure 2 (c), Figure 2 (d) respectively represent laser intensities of 5×10 20 W / cm 2 、1×10 21 W / cm2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 Ablation results of a solid target by laser prepulses of (electron density spatial distribution);

[0022] Figure 3 This is the result diagram of the interaction process between the main pulse of the embodiment of the present invention and a solid target containing a pre-plasma, where Figure 3 (a) is the proton energy spectrum diagram, Figure 3 (b) is the deuterium ion energy spectrum diagram, Figure 3 (c) is the proton angular distribution diagram, Figure 3 (d) is the deuterium ion angular distribution diagram;

[0023] Figure 4 This is the structure diagram of the cubic converter and the wrapped cube of the embodiment of the present invention, where Figure 4 (a) is the structure diagram of the cubic converter, Figure 4 (b) is the structure diagram of the wrapped cube;

[0024] Figure 5 This is the neutron energy spectrum of the reaction between the ion beam driven by the interaction of lasers with different intensities and the cubic converter of the embodiment of the present invention, where Figure 5 (a), Figure 5 (b), Figure 5 (c), Figure 5 (d) respectively represent the neutron energy spectra of the reaction between the ion beam driven by the interaction of lasers with intensities of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 and the cubic converter;

[0025] Figure 6 This is the neutron angular distribution of the reaction between the ion beam driven by the interaction of lasers with different intensities and the cubic converter of the embodiment of the present invention, where Figure 6 (a), Figure 6 (b), Figure 6 (c), Figure 6 (d) respectively represent the neutron angular distributions of the reaction between the ion beam driven by the interaction of lasers with intensities of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2, 4×10 21 W / cm 2 The neutron angular distribution of the reaction between the ion beam driven by the interaction of a laser with a solid target at 4×10 21 W / cm 2 and a cubic converter;

[0026] Figure 7 This is a comparison chart of the neutron yields of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and a cubic converter;

[0027] Figure 8 This is the neutron energy spectrum of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and a wrapped converter, where Figure 8 (a), Figure 8 (b), Figure 8 (c), Figure 8 (d) respectively represent the neutron energy spectra of the reaction between the ion beam driven by the interaction of a laser with a solid target at 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , and 4×10 21 W / cm 2 and a wrapped converter; 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 The neutron angular distribution of the reaction between the ion beam driven by the interaction of a laser with a solid target at 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , and 4×10 21 W / cm 2 and a wrapped converter;

[0028] Figure 9 This is a comparison chart of the neutron yields of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and a wrapped converter, where Figure 9 (a), Figure 9 (b), Figure 9 (c), Figure 9 (d) respectively represent the neutron yields of the reaction between the ion beam driven by the interaction of a laser with a solid target at 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , and 4×10 21 W / cm 2 and a wrapped converter; 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 The neutron yield comparison chart of the reaction between the ion beam driven by the interaction of a laser with a solid target at 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , and 4×10 21 W / cm 2 and a wrapped converter;

[0029] Figure 10 This is a comparison chart of the neutron yields of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and a wrapped converter;

[0030] Figure 11 This is a comparison chart of the neutron yields of the reaction of four groups of converters in the embodiments of the present invention under the ion beam driven by the interaction of lasers with different intensities and a solid target;

[0031] Figure 12 Schematic structural diagram of the converter for the laser beam target neutron source according to the embodiment of the present invention. Specific embodiments

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Figure 1 Schematic diagram of the numerical simulation study according to the embodiment of the present invention; Figure 2 Results diagram of ablation of a solid target by different intensity laser prepulses according to the embodiment of the present invention (spatial distribution of electron density), where Figure 2 (a), Figure 2 (b), Figure 2 (c), Figure 2 (d) respectively represent the results diagrams of ablation of a solid target by laser prepulses with laser intensities of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 (spatial distribution of electron density); Figure 3 Results diagram of the interaction process between the main pulse and the solid target containing pre-plasma according to the embodiment of the present invention, where Figure 3 (a) is the proton energy spectrum diagram, Figure 3 (b) is the deuteron ion energy spectrum diagram, Figure 3 (c) is the proton angular distribution diagram, Figure 3 (d) is the deuteron ion angular distribution diagram; Figure 4 Structural diagrams of the cubic converter and the wrapped cube according to the embodiment of the present invention, where Figure 4 (a) is the structural diagram of the cubic converter, Figure 4 (b) is the structural diagram of the wrapped cube; Figure 5 Neutron energy spectra of the reaction between the ion beam driven by the interaction of different intensity lasers with the solid target and the cubic converter according to the embodiment of the present invention, where Figure 5 (a), Figure 5 (b), Figure 5 (c), Figure 5 (d) respectively represent laser intensities of 5×10 20 W / cm 2, 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 of the neutron energy spectrum of the reaction between the ion beam driven by the interaction of a laser with intensities of 1×10 Figure 6 This is the neutron angular distribution of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and the cubic converter, where Figure 6 (a), Figure 6 (b), Figure 6 (c), Figure 6 (d) respectively represent the neutron angular distributions of the reaction between the ion beam driven by the interaction of lasers with intensities of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 and the cubic converter; Figure 7 This is the comparison chart of the neutron yields of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and the cubic converter; Figure 8 This is the neutron energy spectrum of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and the encapsulated converter, where Figure 8 (a), Figure 8 (b), Figure 8 (c), Figure 8 (d) respectively represent the neutron energy spectra of the reaction between the ion beam driven by the interaction of lasers with intensities of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 and the encapsulated converter; Figure 9 This is the neutron angular distribution of the reaction between the ion beam driven by the interaction of lasers with different intensities in the embodiments of the present invention and the encapsulated converter, where Figure 9 (a), Figure 9 (b), Figure 9 (c), Figure 9 (d) respectively represent the neutron angular distributions of the reaction between the ion beam driven by the interaction of lasers with intensities of 5×10 20 W / cm 2 , 1×10 21W / cm 2 、 2×10 21 W / cm 2 、 4×10 21 W / cm 2 Comparison diagram of neutron yields of reactions between ion beams driven by the interaction of laser and solid targets and encapsulated converters; Figure 10 It is a comparison diagram of neutron yields of reactions between ion beams driven by the interaction of lasers with different intensities and solid targets in the embodiments of the present invention; Figure 11 It is a comparison diagram of neutron yields of four groups of converters in the embodiments of the present invention under the reaction of ion beams driven by the interaction of lasers with different intensities and solid targets; Figure 12 It is a schematic structural diagram of a converter for a laser beam target neutron source in the embodiments of the present invention.

[0034] As Figure 12 shown, the converter for a laser beam target neutron source in this embodiment includes a front plate, a surrounding side plate, and a rear plate. The front plate, the surrounding side plate, and the rear plate enclose to form a sealed inner cavity, and the sealed inner cavity is filled with inclusions to form an encapsulated cubic structure; at least one of the front plate, the surrounding side plate, and the rear plate is made of a material with stable chemical properties, good mechanical properties, and easy to form; the inclusions are filled with substances with excellent neutron generation ability. The converter for a laser beam target neutron source of the present invention effectively prevents the leakage and diffusion of highly toxic inclusions (such as pure beryllium materials, beryllium powder) with strong neutron generation ability through the design of the encapsulation layer, avoids the pollution of the target chamber, and thus significantly improves the safety of the experiment; the inclusions are filled with substances with excellent neutron generation ability (such as beryllium). On the premise of not affecting its neutron generation ability, the encapsulation structure ensures the stability and efficiency of the neutron source; the encapsulated cubic structure can constrain the divergence angle of neutrons, improve the collimation of the neutron beam, and thus enhance the forwardness of the neutron source, which is of great significance for applications that require highly directional neutron beams (such as neutron radiography and material analysis); combined with optimized design, the converter structure of the present invention helps to reduce the neutron pulse width, thereby improving the energy resolution of the neutron source and making it more suitable for high-precision applications such as fast neutron resonance imaging; the design of the converter of the present invention realizes the miniaturization and compactness of the converter through optimizing material selection and structural layout, which is beneficial to the overall miniaturization and low-cost goal of the laser beam target neutron source; by adjusting the composition and structure of the inclusions, the converter can adapt to different neutron energy requirements and meet various applications from fast neutrons to thermal neutrons. The converter for a laser beam target neutron source of the present invention and its optimized design method not only improve the safety of the experiment and the performance of the neutron source, but also provide technical support for the popularization of the laser beam target neutron source in high-precision applications.

[0035] In this embodiment, at least one of the front plate, the surrounding side plates, and the rear plate is made of LiH, LiF, or LiD. In the design of the converter for the laser beam target neutron source, at least one of the front plate, the surrounding side plates, and the rear plate is made of LiH, LiF, or LiD, and these materials play an important role as target materials. Using a LiD composite component target as the neutron converter can effectively increase the neutron yield of the laser neutron source. Compared with the LiF converter, in addition to the p-Li and d-Li reaction channels, the LiD converter can also have two additional reaction channels, p-D and d-D. Therefore, the multi-reaction channel advantages of the laser-accelerated protons and deuterium ions can be fully utilized to increase the neutron generation probability. Experimental results show that compared with the LiF converter, the LiD converter can bring a 2- to 3-fold increase in the neutron yield, reaching a maximum neutron yield of 5.2×10 8 n / sr, and has better forwardness. The experiment also distinguished the contributions of the multi-reaction channels and proved that the increase in the neutron yield mainly comes from the p-D reaction.

[0036] In this embodiment, the inlay is made of beryllium powder. Optionally, the material of the inlay is not limited to Be, and it can also be other materials with good neutron generation ability. When the inlay is made of beryllium powder, since beryllium has a strong "braking" effect on neutrons, it is an excellent neutron moderator in the "atomic boiler". Beryllium also plays an important role in the atomic energy industry, that is, as a reflector for atomic reactors. The oxide of beryllium has a melting point as high as 2450°C, has very good high-temperature resistance, and can reflect neutrons back like a mirror reflects light. Therefore, the oxide of beryllium is a high-quality material for manufacturing the neutron reflection layer. In addition, beryllium-9 will react with neutrons with an energy higher than 1.9 MeV to produce beryllium-8 and two neutrons, and beryllium-8 will immediately split into two alpha particles. So for high-energy neutrons, beryllium is a neutron multiplier because it releases more neutrons than it absorbs. After beryllium-9 absorbs low-energy neutrons, it will also generate tritium, helium nuclei, and electrons. When beryllium-9 is bombarded by high-energy alpha particles, it will also release neutrons. Beryllium-9 will undergo a nuclear reaction with alpha particles to generate carbon-12 and a neutron. Beryllium will also release neutrons under the impact of deuterium ions and protons. Therefore, in the laboratory, beryllium can be irradiated with radium, polonium, and plutonium as a neutron source.

[0037] In this embodiment, the plate thickness of the front plate and / or the rear plate is 0.1 cm to 0.6 cm. By adjusting the thickness of the plate, the neutron generation efficiency can be controlled. A thinner plate (plate thickness less than 0.1 cm) may allow more neutrons to escape, while a thicker plate (plate thickness greater than 0.6 cm) may provide more opportunities for neutron generation, but may also absorb or scatter some neutrons; plates of different thicknesses may affect the energy distribution of neutrons; an appropriate plate thickness helps to generate neutrons within a specific energy range, which may be necessary for certain applications; while maintaining the overall structural stability of the converter, an appropriately thick plate helps to withstand the heat and mechanical stresses generated during the laser beam-target interaction; by controlling the thickness of the plate, neutron leakage can be controlled to a certain extent, thereby improving the safety of the experiment.

[0038] In this embodiment, the height of the surrounding side plates in the front-rear direction is 1 cm to 8 cm; the plate thickness of the surrounding side plates is 0.1 cm to 0.5 cm. By adjusting the thickness and height of the side plates, the neutron generation efficiency can be controlled. A thinner plate may allow more neutrons to escape, while a thicker plate may provide more opportunities for neutron generation, but may also absorb or scatter some neutrons; side plates of different thicknesses and heights may affect the energy distribution of neutrons, and appropriate design helps to generate neutrons within a specific energy range, which may be necessary for certain applications; while maintaining the overall structural stability of the converter, side plates of appropriate thickness and height help to withstand the heat and mechanical stresses generated during the laser beam-target interaction; by controlling the thickness and height of the side plates, neutron leakage can be controlled to a certain extent, thereby improving the safety of the experiment. If the side plates are too thin (side plate thickness less than 0.1 cm), they may not be able to effectively support the structure, resulting in structural instability and may not be able to effectively generate neutrons. If the side plates are too thick (side plate thickness greater than 0.5 cm), they may absorb too many neutrons, reducing the neutron yield and increasing the weight and cost of the structure. If the height of the side plates is too low (side plate height less than 1 cm), it may not be able to cover enough reaction area, reducing the neutron yield; if the height of the side plates is too high (side plate height greater than 8 cm), it may increase the complexity and cost of the structure and may also affect the distribution and directionality of neutrons. The reasonable design of the surrounding side plates is crucial for the performance of the laser beam-target neutron source.

[0039] In this embodiment, the side lengths of the front plate and / or the rear plate and / or the surrounding side plates are 3 cm to 10 cm. Appropriate side lengths help control the neutron generation efficiency. If the side lengths are too small, the neutron generation space may be limited, while if the side lengths are too large, uneven energy distribution may occur, affecting the neutron generation efficiency. While maintaining the overall structural stability of the converter, side lengths in the range of 3 cm to 10 cm help withstand the heat and mechanical stresses generated during the laser beam-target interaction process. By controlling the side lengths of the plates, neutron leakage can be controlled to a certain extent, thereby improving the safety of the experiment. If the side lengths are less than 3 cm, it may limit the neutron generation space, reduce the neutron yield, and may not effectively support the structure, resulting in structural instability. If the side lengths are greater than 10 cm, it may increase the weight and cost of the structure, and may also affect the neutron distribution and directionality, reducing the collimation ratio of the neutron beam, and thus affecting the resolution of neutron radiography. In addition, too large side lengths may lead to uneven energy distribution, affecting the neutron generation efficiency.

[0040] In this embodiment, at least one of the front plate, the rear plate, and the surrounding side plates is a lithium hydride ceramic plate prepared by the warm isostatic pressing method. The lithium hydride ceramic plate prepared by the warm isostatic pressing method plays an important role in the converter for the laser beam-target neutron source. The warm isostatic pressing technology (WIP) is a multi-purpose technology and is applied in various industries such as ceramics, metals, composites, and electronic components. This process usually applies pressure and heat to materials at a temperature below 100 °C to obtain high-density, near-net-shaped components with excellent mechanical and electrical properties. In the ceramic industry, WIP is widely used to produce high-quality monolithic multilayer ceramic electronic components, such as multilayer ceramic capacitors (MLCC), multilayer ceramic inductors (MLCI), and low-temperature co-fired ceramics (LTCC). Warm isostatic pressing can eliminate internal defects such as pores, cracks, shrinkage porosity, segregation, and stress in products, improving the performance of products. Using the warm isostatic pressing method can effectively solve the problem of low density of existing lithium hydride products. The density of the prepared products exceeds 99.2%, reaching 99.2% - 99.7%, and the crushing strength can reach 145 MPa - 210 MPa. This shows that the lithium hydride ceramic plate prepared by the warm isostatic pressing method has high density and good mechanical properties, which is beneficial to improving the neutron generation efficiency and the overall performance of the converter.

[0041] In this embodiment, a high-bonding glue is used for sealing connection between the front plate and the surrounding side plates and / or between the surrounding side plates and the rear plate. The high-bonding glue can ensure the sealed connection between the plates, prevent neutron leakage during the experiment, and thus improve the safety and reliability of the experiment; by using the high-bonding glue, the overall structural stability of the converter can be enhanced, enabling it to withstand the heat and mechanical stresses generated during the laser beam-target interaction; the use of the high-bonding glue helps to maintain the integrity inside the converter, thereby improving the neutron generation efficiency. It can ensure that inclusions such as beryllium powder and other materials are effectively encapsulated without affecting the neutron generation ability. The high-bonding glue should have the following characteristics and not affect the function of the converter for the laser beam-target neutron source: remain stable in the high-temperature and radiation environment generated by the laser beam-target interaction, without decomposing or releasing substances that affect the neutron generation efficiency; be able to firmly bond plates of different materials to ensure the durability and reliability of the connection; not chemically react with other materials inside the converter during the experiment to avoid generating harmful substances or affecting the performance of the neutron source. For example, a fast-drying and precisely grindable adhesive for laser ablation sample target preparation such as CN110763544A can be used, which has no effect on in-situ laser analysis, has strong adhesion and is fast-drying, and is suitable for laser ablation sample target preparation.

[0042] Optimization design method for converter of laser beam target neutron source in this embodiment, comprising the following steps: S100. Select two converter structures. The first one in this embodiment adopts a cube structure of single material, and the second one adopts a wrapped cube structure; S200. Conduct numerical simulations comprehensively using radiation hydrodynamics code FLASH, particle simulation code EPOCH and Monte Carlo code Geant4; S300. Focus on the typical parameter indexes of the output light of a multi-petawatt femtosecond laser device. Considering the laser prepulse and the post-target contamination layer, obtain the quality characteristics of intense current ion beams driven by lasers with different intensities, and then obtain the influence law of the material, geometric shape and position of the converter structure on the quality of the beam target neutron source, and further improve the converter optimization design scheme for neutron yield and forward-side neutron yield ratio. By selecting two converter structures, namely the cube structure of single material and the wrapped cube structure, and conducting numerical simulations comprehensively using radiation hydrodynamics code FLASH, particle simulation code EPOCH and Monte Carlo code Geant4, this method focuses on the typical parameter indexes of the output light of a multi-petawatt femtosecond laser device. Considering the laser prepulse and the post-target contamination layer, obtain the quality characteristics of intense current ion beams driven by lasers with different intensities. Through this process, the influence law of the material, geometric shape and position of the converter structure on the quality of the beam target neutron source can be obtained, and further improve the converter optimization design scheme for neutron yield and forward-side neutron yield ratio; Through optimization design, the generation efficiency of neutrons can be improved, thus increasing the total neutron yield; Improving the neutron yield and forward-side neutron yield ratio helps to improve the directivity of the neutron beam, which is crucial for applications such as neutron radiography and neutron activation analysis; Through numerical simulation and optimization design, the structural stability of the converter during the laser beam-target interaction process can be ensured, thus improving the reliability of the experiment; Optimization design helps to control neutron leakage, thus improving the safety of the experiment; Through optimization design, the material and manufacturing costs can be reduced while ensuring performance, and the economy of the laser beam target neutron source can be improved. It is possible to obtain the quality characteristics of intense current ion beams driven by lasers with different intensities, and then obtain the influence law of the material, geometric shape and position of the converter structure on the quality of the beam target neutron source, and further improve the converter optimization design scheme for neutron yield and forward-side neutron yield ratio; This method helps to increase neutron yield, optimize neutron directivity, enhance structural stability and improve experimental safety, and also helps to reduce costs and improve economy.

[0043] In this embodiment, a cubic structure and a wrapped cubic structure are respectively selected for analysis; the length and width of the converter structure are both 4 cm, the thickness of the converter structure is designed to be 5 cm, and the distance between the converter structure and the throwing target is set to 1 cm; the material of the cubic structure is selected from LiH, LiF, LiD or Be, and the converter is a single material component; the outer material of the wrapped cubic structure is selected from LiH, LiF or LiD, and the embedded material is selected from Be; based on the simulation results of neutrons generated by the interaction of ion beams driven by lasers with different intensities and different converter structures, the neutron generation ability is obtained. This optimization design method helps to increase the neutron yield, optimize the neutron directivity, enhance the structural stability and improve the experimental safety, and also helps to reduce costs and improve economic efficiency. In addition, through numerical simulation and optimization design, the structural stability of the converter during the interaction between the laser beam and the target can be ensured, thereby improving the reliability of the experiment.

[0044] In implementation, the present invention comprehensively uses the radiation hydrodynamics program FLASH, the particle simulation program EPOCH, and the Monte Carlo program Geant4 to carry out numerical simulation research. The specific research methods are as follows:

[0045] (1) Radiation hydrodynamics method: The laser ASE and pre-pulse ablation of the solid target involve many physical processes such as laser energy deposition, electron-ion heat exchange, heat conduction, and radiation diffusion. The radiation hydrodynamics method is the most suitable simulation method. The present invention uses the FLASH program (Fast, Low-mass Astrophysical Simulations with High-accuracy) to numerically simulate this process. The FLASH program is a radiation magnetohydrodynamics program developed by the FLASH Research Center of the University of Chicago in the United States. This program is based on the Eulerian framework with a fixed grid and uses the finite volume method to solve the control equations. The latest version 4.7 of this program was released in January 2023. Its greatest advantage is the complete diffusion magnetohydrodynamic model, which adds the latest transport coefficients in the material module, significantly improving the simulation ability of the program in the field of high energy density physics and being very suitable for simulating the interaction between the laser ASE or pre-pulse and the solid target in the present invention.

[0046] (2) Particle-in-Cell (PIC) method: The PIC method obtains the macroscopic properties and motion laws of plasmas by tracking the motion behaviors of a large number of charged particles in external and self-consistent electromagnetic fields. It is a very effective computer simulation method for studying the kinetic behaviors of plasmas. The interaction between an ultra-intense laser and a solid target is a highly nonlinear physical process, which contains both rich collective interactions and various instabilities. As a "numerical experiment", plasma particle simulation has the advantages of good repeatability, intuitive and rich physical pictures, and easy parameter studies, and is particularly suitable for studying such highly nonlinear physical processes. The present invention uses the PIC program EPOCH to carry out research on the interaction between lasers and plasmas. This program is an open-source parallel particle simulation program developed by the CFSA team at the University of Warwick in the UK. The program has complete functions and rich modules. According to user feedback and requirements, the development team will continuously optimize the program algorithm and expand the program functions. In addition, there are various choices for data processing and visualization of this program. Corresponding data loading scripts are provided for various software such as MatLab, Visit, IDL, and Python, which can conveniently perform visual analysis on the simulation results and obtain rich physical pictures. The calculation results relying on the EPOCH program have been confirmed by a large number of experiments, and this program has become the international mainstream program for studying the interaction between lasers and matter currently.

[0047] (3) Monte Carlo method: The Monte Carlo method is a statistical method based on random sampling, and estimates the results through a large number of repeated random experiments. Since the motion trajectories, flight directions, reaction types, etc. of neutrons all follow the principle of randomness, it is very suitable for simulating the motion and reactions of neutrons. Geant4 is an open-source simulation software developed based on C++ (developed by CERN). Its design is to expose the physical models used, handle complex geometries, and make it optimally used in different fields (such as the fields of particle physics and nuclear physics). Geant4 is a toolkit for simulating the process of particle-matter interactions and has a complete set of functions for these processes. The physical processes cover electromagnetic, hadronic, and optical processes, and also include a series of particles, materials, and elements. In some cases, the energy of these particles can be as low as 250 eV at the lowest and extend to the TeV level at the highest. When defining and implementing software components, all aspects of the simulation process include: the geometric model of the entire system, all events in the process, and the capture process of the detector, etc. In the research of the present invention, the information of the accelerated ions obtained in PIC is first imported into Geant4 in the form of a data stream for relevant simulations of neutron generation.

[0048] The research schematic diagram is as Figure 1 . Figure 1Shows a schematic diagram of a numerical simulation study that comprehensively uses three different programs: the radiation hydrodynamics program FLASH, the particle simulation program EPOCH, and the Monte Carlo program Geant4. These programs are used to simulate complex physical processes such as nuclear reactions, particle transport, and radiation hydrodynamics transport, etc. In Figure 1 :

[0049] The left - hand figure represents a high - energy laser beam. The high - energy laser includes a prepulse and a main pulse.

[0050] The "throw - target" structure in the middle represents the material for the interaction between the laser and the matter. The process of simulating the interaction between the high - energy laser prepulse and the matter using the FLASH program. FLASH is a program for simulating hydrodynamics and radiation transport, and it can simulate physical processes in high - temperature and high - pressure environments, such as the plasma behavior in nuclear fusion reactions. Using the radiation hydrodynamics program FLASH, study the ablation effects of amplified spontaneous emission (ASE) with different intensities and the laser rise - edge on the solid target, and obtain the influence laws of the prepulse intensity, incident angle, etc. on the density and temperature distribution of the pre - plasma. The interaction process between the main pulse and the throw - target ablated by the prepulse is simulated using the particle simulation program EPOCH. EPOCH is a particle simulation program dedicated to simulating the motion and interaction of charged particles in electromagnetic fields. Using the particle simulation program EPOCH, study the laser - ion acceleration process considering the existence of the actual pre - plasma and the target - back contamination layer, and obtain the quality characteristic parameters of the proton beam and ion beam under different laser intensities.

[0051] The "Converter" structure on the right represents the converter. The material that is bombarded by the high - energy ions generated by irradiating the throw - target with the laser and produces neutrons through the beam - target nuclear reaction is called the converter. This process is simulated using the Monte Carlo program Geant4. Geant4 is a widely used Monte Carlo program for simulating the transport and interaction of particles in matter, including neutrons, photons, electrons, etc. Using the Monte Carlo program Geant4, study the transport and nuclear reaction processes of intense proton / ion beams with different parameters in the converter, and explore the influence laws of the incident ion beam quality parameters and the converter temperature on the neutron yield, energy, and angular distribution.

[0052] Figure 1The colored circles (yellow, blue, and brown) represent different particle types, such as protons (p⁺), neutrons (n), and deuteron ions (D⁺), which are traced and analyzed in different simulation programs. The entire schematic diagram shows the simulation process from FLASH to EPOCH and then to Geant4, indicating that the full - process numerical simulation study on the converter optimization in the laser - beam - target neutron source comprehensively using the radiation - hydrodynamics program FLASH, the particle simulation program EPOCH, and the Monte Carlo program Geant4 in the present invention is completely feasible. The FLASH program is used to simulate the physical processes of ASE and pre - pulse ablation of solid targets, obtaining state parameters such as pre - plasma density and temperature; the EPOCH program is used to simulate the dynamics of laser - plasma nonlinear interactions considering the presence of pre - plasma and the target - back contamination layer, obtaining quality characteristic parameters such as ion - beam energy spectra and angular distributions; the Geant4 program is used to simulate the transport of intense ion beams with different quality characteristics in the converter and the detailed process of neutron generation by nuclear reactions, obtaining information such as neutron energy spectra, divergence angles, and yields.

[0053] This comprehensive simulation method can help researchers more comprehensively understand and predict experimental results, optimize designs, and guide experimental operations.

[0054] Figure 2 are for different laser intensities (5×10 20 W / cm 2 、1×10 21 W / cm 2 、2×10 21 W / cm 2 、4×10 21 W / cm 2 , with the laser pulse widths all set to 30 fs and the focal spot radii all being 4.8 µm), showing the ablation results (spatial distribution of electron density) of the pre - pulse of the laser on the solid target (5 - µm carbon - deuterium target plus 20 - nm carbon - hydrogen contamination layer). The horizontal axis (x - axis) and vertical axis (y - axis) of each sub - figure represent spatial coordinates in micrometers (µm), and the color bar represents the distribution of electron density, with the color changing from blue (low electron density) to red (high electron density).

[0055] 5×10 20 W / cm 2 : At this laser intensity, the distribution of electron density is relatively concentrated, mainly concentrated near the surface of the target, forming a relatively narrow high - density region.

[0056] 1×10 21 W / cm 2 : As the laser intensity increases, the high - electron - density region becomes wider, indicating an expanded ablation region. The distribution of electron density begins to extend into the interior of the target.

[0057] 2×10 21 W / cm 2 : At this intensity, the ablation region further expands, and the distribution of electron density becomes more uniform, indicating that both the surface and the interior of the target are significantly ablated.

[0058] 4×10 21 W / cm 2 : At the highest laser intensity, the ablation region reaches its maximum, and the distribution of electron density is very extensive, almost covering the entire surface and interior of the target. This indicates that at high laser intensities, the ablation of the target material is very severe.

[0059] In summary, as the laser intensity increases, the ablation region of the solid target gradually expands, and the distribution of electron density also changes from concentrated to extensive. High laser intensities result in more severe ablation of the target material, and the electron density increases significantly throughout the surface and interior of the target. These results are of great significance for understanding the physical process of the interaction between laser and solid target, as well as for optimizing the laser ablation process.

[0060] Figure 3 are the results of the interaction process between the main pulse and the solid target containing pre-plasma, specifically including the particle energy distribution and the distribution of particles in phase space. The figure is divided into four subgraphs, which respectively show the distributions of hydrogen ions ( ) and deuterium ions ( ) at different laser intensities. Specifically as follows:

[0061] Figure 3 (a) and Figure 3 (b) subgraphs: Particle energy distribution.

[0062] Figure 3 (a) Energy distribution: Shows the energy distribution of hydrogen ions at different laser intensities (5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 ). The horizontal axis represents the particle energy (ε / MeV), and the vertical axis represents the number of particles (dN / dε). As the laser intensity increases, the energy distribution of hydrogen ions shifts towards higher energies, indicating that the higher the laser intensity, the more high-energy hydrogen ions are produced.

[0063] Figure 3 (b) Energy distribution: Shows the energy distribution of deuterium ions at different laser intensities. Similar to hydrogen ions, as the laser intensity increases, the energy distribution of deuterium ions also shifts towards higher energies.

[0064] Figure 3 (c) and Figure 3 (d) Subfigure: Distribution of particles in phase space.

[0065] Figure 3 (c) Phase space distribution: Shows the distribution of hydrogen ions in phase space. The horizontal and vertical axes represent two dimensions of the phase space respectively. Curves of different colors represent different laser intensities. As the laser intensity increases, the distribution of hydrogen ions in phase space becomes more concentrated, indicating that the higher the laser intensity, the stronger the emission directionality of hydrogen ions.

[0066] Figure 3 (d) Phase space distribution: Shows the distribution of deuterium ions in phase space. Similar to hydrogen ions, as the laser intensity increases, the distribution of deuterium ions in phase space also becomes more concentrated.

[0067] In summary, as the laser intensity increases, the energy distributions of hydrogen ions and deuterium ions shift towards higher energies, indicating that the higher the laser intensity, the more high-energy ions are produced. In phase space, as the laser intensity increases, the distributions of hydrogen ions and deuterium ions become more concentrated, indicating that the higher the laser intensity, the stronger the emission directionality of the ions. These results are of great significance for understanding the physical process of laser-solid target interaction and optimizing the design of laser plasma sources.

[0068] For the transport of ion beams in the converter and the neutron generation process, the present invention uses the Monte Carlo program Geant4 for simulation. The present invention sets two converter structures, one is the common cube structure in the laser beam target neutron source for comparison, and the other is the wrapped cube structure designed by the present invention, as Figure 4 shown.

[0069] First, select the common cube structure in the laser beam target neutron source for analysis. The simulation results of neutrons generated by the interaction of ion beams driven by lasers of different intensities with the cube-shaped converter are as Figure 5 , Figure 6 , Figure 7 , the length and width of this converter are both 4 cm, the thickness of the converter is designed to be 5 cm, the distance between the converter and the projectile target is set to 1 cm, the materials selected are LiH, LiF, LiD, Be, and the converter is a single material component.

[0070] Figure 5 Shows the neutron energy spectra generated by the interaction of ion beams driven by lasers of different intensities with the cubic converter. The figure contains four subfigures, each subfigure corresponding to a different laser intensity: 5×10 20W / cm 2 、 1×10 21 W / cm 2 、 2×10 21 W / cm 2 、 4×10 21 W / cm 2 。 In each sub - figure, the neutron energy spectra for lithium hydride (LiH), lithium fluoride (LiF), lithium deuteride (LiD), and beryllium (Be) as target materials are shown respectively. Specifically as follows:

[0071] The horizontal axis (ε / MeV): represents the energy of neutrons, with the unit of mega - electron volts (MeV).

[0072] The vertical axis (dN / dε): represents the number of neutrons, that is, the number of neutrons within the unit energy interval, reflecting the yield of neutrons with different energies.

[0073] Curves of different colors: represent different target materials (LiH, LiF, LiD, Be).

[0074] Specific analysis:

[0075] 5×10 20 W / cm 2 : At the lowest laser intensity, the neutron energy spectra generated by all target materials are relatively low and the energy distribution is narrow.

[0076] 1×10 21 W / cm 2 : As the laser intensity increases, the neutron yield increases significantly and the energy distribution becomes wider, indicating that the neutron generation efficiency is higher at higher laser intensities.

[0077] 2×10 21 W / cm 2 : The neutron yield further increases, and the neutron energy spectra of different target materials begin to show more obvious differences. The neutron energy spectrum generated when beryllium (Be) is used as the target material is the highest.

[0078] 4×10 21 W / cm 2 : At the highest laser intensity, the neutron yield reaches the maximum, and the neutron energy spectrum generated when beryllium (Be) is used as the target material is significantly higher than that of other materials, indicating that beryllium is the most effective neutron - generating target material at high laser intensities.

[0079] In summary, as the laser intensity increases, the neutron yield increases significantly, and the energy distribution becomes broader. There are differences in the neutron energy spectra produced by different target materials at the same laser intensity, and beryllium (Be) exhibits the highest neutron yield at high laser intensities. These results are of great significance for selecting appropriate target materials to optimize the performance of neutron sources, especially in cases where high-efficiency neutron generation is required.

[0080] Figure 6 Shows the neutron angular distribution resulting from the reaction of ion beams driven by lasers of different intensities interacting with solid targets and a cubic converter. The figure contains four subgraphs, each corresponding to a different laser intensity: 5×10 20 W / cm 2 、1×10 21 W / cm 2 、2×10 21 W / cm 2 、4×10 21 W / cm 2 . In each subgraph, the neutron angular distributions are shown for lithium hydride (LiH), lithium fluoride (LiF), lithium deuteride (LiD), and beryllium (Be) as target materials. Specifically as follows:

[0081] Polar plots: Each subgraph uses a polar plot to show the angular distribution of neutrons, where the radius represents the number of neutrons and the angle represents the direction of neutron emission.

[0082] Curves of different colors: Represent different target materials (LiH, LiF, LiD, Be).

[0083] Effect of laser intensity: As the laser intensity increases, the total number of neutrons (the magnitude of the radius) increases significantly, indicating that the higher the laser intensity, the more neutrons are produced. At lower laser intensities (5×10 20 W / cm 2 ), the neutron distribution is relatively narrow and mainly concentrated in a specific direction. At higher laser intensities (4×10 21 W / cm 2 ), the neutron distribution becomes broader, indicating a wider directionality of neutron emission.

[0084] Effect of target material: There are differences in the neutron angular distributions produced by different target materials at the same laser intensity. When beryllium (Be) is used as the target material, the neutron distribution is relatively broad, indicating that beryllium has better directionality in neutron production. The neutron distributions of lithium hydride (LiH), lithium fluoride (LiF), and lithium deuteride (LiD) are relatively narrow, indicating that these materials have poorer directionality in neutron production.

[0085] In summary, as the laser intensity increases, the total number of neutrons increases significantly, and the directionality of neutron emission becomes broader. There are differences in the neutron angular distributions produced by different target materials at the same laser intensity, and beryllium (Be) exhibits better directionality. These results are of great significance for selecting appropriate target materials to optimize the performance of neutron sources, especially in applications that require neutron beams in specific directions.

[0086] Figure 7 Shows the neutron yields resulting from the reaction of ion beams with a cubic converter under the interaction of lasers with different intensities and solid targets. Bar graphs are used in the figure to represent the neutron yields of different target materials (LiH, LiF, LiD, Be) at different laser intensities (5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 ). Specifically as follows: N .

[0087] Horizontal axis: Represents different laser intensity levels, from 5×10 20 W / cm 2 to 4×10 21 W / cm 2 .

[0088] Vertical axis: Represents the neutron yield N , using a logarithmic scale, ranging from 10 6 to 10 11 .

[0089] Bars of different colors: Represent different target materials. Blue represents lithium hydride (LiH), orange represents lithium fluoride (LiF), yellow represents lithium deuteride (LiD), and purple represents beryllium (Be). Specific analysis:

[0090] The neutron yield increases with the increase of laser intensity: For all target materials, as the laser intensity increases from 5×10 20 W / cm 2 to 4×10 21 W / cm 2 , the neutron yield increases significantly. This indicates that the laser intensity is an important factor affecting the neutron yield.

[0091] Comparison of neutron yields of different target materials: At all laser intensities, beryllium (Be) as the target material produces the highest neutron yield, followed by lithium deuteride (LiD), lithium fluoride (LiF), and lithium hydride (LiH) has the lowest neutron yield.

[0092] This is related to the nuclear reaction cross-section and neutron production mechanism of different materials.

[0093] Logarithmic growth of neutron yield: Since the vertical axis is a logarithmic scale, it can be seen that the neutron yield shows a nonlinear growth trend with the increase of laser intensity, especially from 2×10 21 W / cm 2 to 4×10 21 W / cm 2 The increase in neutron yield is more significant in the intensity range of .

[0094] In summary, Figure 7 The neutron yields of different target materials at different laser intensities are clearly shown, providing an important reference for selecting appropriate target materials and optimizing laser parameters. Beryllium (Be) as a target material performs best in producing neutrons, especially at high laser intensities. These results are of great significance for designing efficient neutron sources and optimizing related experiments.

[0095] The neutron generation capabilities of the four materials are as follows: Be, LiD, LiH, LiF. However, after investigation, it was found that pure beryllium material is in powder form and highly toxic, which will contaminate the target chamber during the experiment, so it is very unfavorable to carry out laser beam target neutron source experiments. Based on this, the present invention designs a wrapped cubic structure, such as Figure 4 (b) The wrapped cube consists of a front plate, a back plate, a surrounding side plate (hollow shell) and an embedded object. The advantage of this configuration is that the beryllium with the highest neutron production capacity is isolated from the target chamber through a physical barrier, which effectively solves the problem of the target chamber being contaminated by the toxicity of the beryllium material. Figure 8 , Figure 9 , Figure 10 These are the simulation results of different wrapping layers containing Be.

[0096] Figure 8 The neutron energy spectrum produced by the reaction between the driven ion beam and the encapsulated converter under the interaction of laser with different intensities and solid targets is described. The figure contains four sub-graphs, each corresponding to a different laser intensity: 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 In each sub-figure, the neutron energy spectra of different target material combinations (LiH(Be), LiF(Be), LiD(Be)) are shown. The details are as follows:

[0097] Horizontal axis (ε / MeV): represents the energy of neutrons in mega-electron volts (MeV).

[0098] Vertical axis (dN / dε): Represents the number of neutrons, i.e., the number of neutrons within a unit energy interval, on a logarithmic scale, reflecting the yields of neutrons with different energies.

[0099] Curves of different colors: Represent different combinations of target materials. Among them: Red represents LiH(Be), blue represents LiF(Be), and black represents LiD(Be).

[0100] Specific analysis:

[0101] Influence of laser intensity on the neutron energy spectrum: As the laser intensity increases, the overall neutron energy spectrum shifts to the right, indicating an increase in the average energy of neutrons. At the highest laser intensity (4×10 21 W / cm 2 ), the neutron energy spectrum extends to a higher energy range, showing a stronger ability to generate high-energy neutrons. Comparison of different combinations of target materials: At all laser intensities, the neutron energy spectrum generated by the LiD(Be) combination is the highest, indicating that it is superior to LiH(Be) and LiF(Be) in terms of neutron production efficiency. The neutron energy spectra of the LiH(Be) and LiF(Be) combinations are relatively lower, and the difference between them is small.

[0102] Variation of energy distribution: At a lower laser intensity (5×10 20 W / cm 2 ), the neutron energy spectrum is more concentrated, and the energy distribution is narrower. At higher laser intensities, the neutron energy spectrum becomes wider, showing a more extensive neutron energy distribution.

[0103] In summary, Figure 8 demonstrates the influence of different laser intensities and combinations of target materials on the neutron energy spectrum, providing important data for optimizing the design of neutron sources. The LiD(Be) combination shows the highest neutron production efficiency at all tested laser intensities and is the optimal choice of target material. As the laser intensity increases, the average energy of neutrons increases, and the energy distribution becomes wider, which helps to achieve more efficient neutron applications.

[0104] Figure 9 Shows the neutron angular distribution generated by the reaction of an ion beam with a wrapped converter under the interaction of lasers with different intensities and a solid target. The figure contains four subgraphs, each corresponding to a different laser intensity: 5×10 20 W / cm 2 、1×10 21 W / cm 2 、2×10 21 W / cm 2 、4×10 21 W / cm 2。In each subfigure, the neutron angular distributions for different target material combinations (LiH(Be), LiF(Be), LiD(Be)) are shown respectively. Specifically as follows:

[0105] Polar plots: Each subfigure uses a polar plot to show the angular distribution of neutrons, where the radius represents the number of neutrons and the angle represents the direction of neutron emission.

[0106] Curves of different colors: Represent different target material combinations. Red represents LiH(Be), blue represents LiF(Be), and black represents LiD(Be).

[0107] Effect of laser intensity: As the laser intensity increases, the total number of neutrons (the size of the radius) increases significantly, indicating that the higher the laser intensity, the more neutrons are produced. At a relatively low laser intensity (5×10 20 W / cm 2 ), the distribution of neutrons is relatively narrow and mainly concentrated in a specific direction. At a higher laser intensity (4×10 21 W / cm 2 ), the distribution of neutrons becomes wider, indicating a broader directionality of neutron emission.

[0108] Effect of target material combination: There are differences in the neutron angular distributions produced by different target material combinations at the same laser intensity. The LiD(Be) combination produces the largest number of neutrons at all laser intensities, indicating that it has a higher efficiency in neutron production. The LiH(Be) and LiF(Be) combinations produce relatively fewer neutrons, and the difference between them is relatively small.

[0109] In summary, Figure 9 clearly shows the neutron angular distributions of different target material combinations at different laser intensities, providing important references for selecting appropriate target materials and optimizing laser parameters. The LiD(Be) combination performs best in neutron production, especially at high laser intensities. These results are of great significance for designing efficient neutron sources and optimizing related experiments, especially in applications that require neutron beams in specific directions.

[0110] Figure 10 Shows the neutron yields produced by the reaction of the driven ion beam with the encapsulated converter under the interaction of lasers with different intensities and solid targets. This figure uses a bar chart to represent the neutron yields of different target material combinations (LiH(Be), LiF(Be), LiD(Be)) at different laser intensities (5×10 20 W / cm 2 、1×10 21 W / cm 2 、2×10 21 W / cm 2 、4×1021 W / cm 2 ), the neutron yield N . Specifically as follows:

[0111] Horizontal axis: represents different laser intensity levels, ranging from 5×10 20 W / cm 2 to 4×10 21 W / cm 2 .

[0112] Vertical axis: represents the neutron yield N , using a logarithmic scale, ranging from 10 6 to 10 11 .

[0113] The columns of different colors: represent different combinations of target materials. Blue represents LiH(Be), orange represents LiF(Be), and yellow represents LiD(Be).

[0114] Specific analysis:

[0115] The neutron yield increases with the increase in laser intensity: For all combinations of target materials, as the laser intensity increases from 5×10 20 W / cm 2 to 4×10 21 W / cm 2 , the neutron yield increases significantly. This indicates that the laser intensity is an important factor affecting the neutron yield.

[0116] Comparison of neutron yields for different combinations of target materials: At all laser intensities, the LiD(Be) combination produces the highest neutron yield, followed by LiH(Be), and the LiF(Be) combination has the lowest neutron yield. This may be related to the nuclear reaction cross-sections and neutron generation mechanisms of different materials. Logarithmic growth of the neutron yield: Since the vertical axis is a logarithmic scale, it can be seen that the neutron yield shows a non-linear growth trend with the increase in laser intensity, especially in the intensity range from I 3 to I 4, where the growth of the neutron yield is more significant.

[0117] In summary, Figure 10 clearly shows the neutron yields of different combinations of target materials at different laser intensities, providing an important reference for selecting appropriate target materials and optimizing laser parameters. The LiD(Be) combination performs best in neutron production, especially at high laser intensities. These results are of great significance for designing efficient neutron sources and optimizing related experiments, and contribute to more efficient neutron generation and applications.

[0118] Such as Figure 8 , Figure 9 and Figure 10As shown, it is not difficult to find from the above simulation results that the neutron production ability is from large to small, LiD-wrapped Be, LiH-wrapped Be and LiF-wrapped Be. First, LiD-wrapped Be is considered. Since LiD is easily deliquesced when exposed to air and its properties are unstable, it is not considered as the material of the encapsulation layer; the second is LiH-wrapped Be. Ordinary LiH is stable at room temperature, in dry air or oxygen. In humid air, it can be slowly decomposed by atmospheric moisture. However, after investigation, it was found that this material can be prepared by warm isostatic pressing to form a LiH ceramic material with a density of more than 99.2%. It has stable properties, excellent mechanical properties and can effectively alleviate the deliquesce and oxidation of lithium hydride; the last is LiF-wrapped Be. Although LiF has stable chemical properties, its mechanical properties are poor and cannot be used as an encapsulation layer. After comprehensive consideration, LiH is used as the encapsulation layer material and Be is used as the filler. Finally, the neutron yields of the four groups of converters, LiF, LiD, Be and LiH-wrapped Be, under ion beam reactions driven by the interaction of lasers of different intensities and solid targets were compared. The results are as follows Figure 11 .

[0119] like Figure 11 As shown, the neutron yields of four groups of converters under ion beam reactions driven by the interaction of lasers of different intensities and solid targets are shown. By comparing the data, it can be found that the neutron yield of the encapsulated converter designed by the present invention, i.e., the LiH-encapsulated Be-type encapsulated converter, is generally similar to that of the pure Be converter of the same size (neutron yield comparison data is shown in the figure), and is significantly better than the LiF and LiD converters of the same size, proving that the encapsulated converter is feasible.

[0120] Matters not covered by the present invention are known technologies.

[0121] 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.

[0122] The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

[0123] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A converter for a laser - beam - target neutron source, which uses a petawatt femtosecond laser beam to drive the neutron source, is characterized in that it includes a front plate, a surrounding side plate, and a rear plate. The front plate, the surrounding side plate, and the rear plate enclose to form a sealed inner cavity, and the sealed inner cavity is filled with inlays to form a wrapped cube structure; at least one of the front plate, the surrounding side plate, and the rear plate is made of LiD, and high - bonding glue is used for sealing connection between the front plate and the surrounding side plate and / or between the surrounding side plate and the rear plate. The thickness of the surrounding side plate is 0.1 cm to 0.5 cm; The inlay is made of pure beryllium material.

2. The converter for a laser - beam - target neutron source according to claim 1, is characterized in that the inlay uses beryllium powder.

3. The converter for a laser - beam - target neutron source according to claim 1 or 2, is characterized in that the thickness of the front plate and / or the rear plate is 0.1 cm to 0.6 cm.

4. The converter for a laser - beam - target neutron source according to claim 1 or 2, is characterized in that the height of the surrounding side plate in the front - to - rear direction is 1 cm to 8 cm.

5. The converter for a laser - beam - target neutron source according to claim 1 or 2, is characterized in that the side length of the front plate and / or the rear plate and / or the surrounding side plate is 3 cm to 10 cm.

6. The converter for a laser - beam - target neutron source according to claim 1 or 2, is characterized in that at least one of the front plate, the rear plate, and the surrounding side plate is a lithium hydride ceramic plate prepared by the warm isostatic pressing method.

7. An optimization design method for a converter for a laser - beam - target neutron source, which is used to design the converter for a laser - beam - target neutron source according to any one of claims 1 to 6, is characterized in that it includes the following steps: S100. Select two converter structures. The first one is a cube structure made of a single material, and the second one is a wrapped cube structure of the converter for a laser - beam - target neutron source according to any one of claims 1 to 6; S200. Carry out numerical simulations by comprehensively using the radiation - fluid program FLASH, the particle simulation program EPOCH, and the Monte Carlo program Geant4; S300. Focus on the typical parameter indicators of the output light of the petawatt femtosecond laser device. Considering the laser prepulse and the post - target contamination layer, obtain the quality characteristics of the intense - current ion beam driven by lasers with different intensities, and then obtain the influence law of the material, geometric shape, and position of the converter structure on the quality of the beam - target neutron source, and further improve the optimization design scheme of the converter for improving the neutron yield and the ratio of the forward - side neutron yield.

8. The optimization design method for a converter for a laser - beam - target neutron source according to claim 7, is characterized in that select the cube structure and the wrapped cube structure for analysis respectively; the length and width of the converter structure are both 4 cm, the thickness of the converter structure is designed to be 5 cm, and the distance between the converter structure and the throwing target is set to be 1 cm; the material of the cube structure is selected from a single - material component of LiH, LiF, LiD, or Be; the outer material of the wrapped cube structure is selected from LiH, LiF, or LiD, and the inlay material is selected from Be; Simulation results of neutrons generated by the reaction of ion beams driven by the interaction of lasers with different laser intensities with solid targets and different converter structures, and then the neutron generation ability is obtained.

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