A method and system for improving coupling efficiency of a beam target and fusion yield

Abstract

The application discloses a method and system for improving beam-target coupling efficiency and fusion yield, belongs to the field of fusion energy, and particularly relates to the field of inertial confinement fusion. In view of the technical bottleneck of low beam-target coupling efficiency and limited fusion yield in the existing hybrid driven inertial confinement fusion, the application re-distributes the indirect drive beam energy in a specific time window to the direct drive beam through specific energy regulation technology, and combines a high-Z material black cavity with precise laser timing control to realize double improvement of the beam-target coupling efficiency and the fusion yield. The application solves the core problems of the beam-target coupling efficiency bottleneck and the out-of-control driving asymmetry in the prior art, has the advantages of improving the driving asymmetry tolerance and inhibiting the driving asymmetry, and can promote the inertial confinement fusion from scientific verification to engineering application, thereby providing technical support for the practicalization of fusion energy.

Description

Technical Field

[0001] This invention belongs to the field of fusion energy, and particularly relates to the field of inertial confinement fusion (ICF) in the field of fusion energy. Specifically, it relates to a method and system for improving beam-target coupling efficiency and fusion yield, which can effectively improve the energy coupling efficiency between the laser and the fusion target, thereby obtaining higher fusion gain and promoting the engineering application of inertial confinement fusion technology. Background Technology

[0002] Fusion energy, as humanity's "ultimate dream" for energy, boasts outstanding advantages such as being clean, efficient, and rich in fuel reserves, making it a crucial direction for solving future energy crises. Inertial confinement fusion (ICF) is one of the main technological routes to realize the practical application of fusion energy. Its core principle is to drive a fusion target pellet with a high-energy laser, rapidly compressing it to extremely high temperatures and densities under its own inertia, thereby triggering a fusion reaction.

[0003] Currently, both indirect and direct drive principles in existing ICF ignition schemes have been verified through extensive experiments. Among them, the National Ignition Facility (NIF) in the United States was the first to achieve a breakthrough in fusion ignition using the indirect drive method. However, the fusion energy gain of this scheme is severely limited, becoming a key bottleneck restricting the transformation of inertial confinement fusion from scientific verification to engineering application.

[0004] Achieving high-gain fusion faces two major technological challenges: First, the bottleneck of beam-target coupling efficiency. The beam-target coupling efficiency of indirect drive schemes is generally below 15%, with the measured value of the NIF device being only 13%. Although the theoretical limit of direct drive schemes can reach 30%, the current experimental peak is only 22%, and energy utilization efficiency still needs to be significantly improved. Second, runaway implosion symmetry. The coupling effect of laser-plasma instability (LPI) and hydrodynamic instability (HI) can induce drive asymmetry, leading to a 50%-80% reduction in implosion performance. NIF experiments have confirmed that when drive asymmetry > 5%, hot spot pressure loss can be as high as 40%, seriously affecting fusion yield. Therefore, improving beam-target coupling efficiency while ensuring controllable drive asymmetry has become a key breakthrough for increasing fusion yield.

[0005] Hybrid drive, as a novel ICF (Inductively Coupled Fusion) driving scheme, possesses unique advantages such as higher beam-target coupling efficiency than indirect drive, superior driving symmetry compared to direct drive, and greater tolerance for driving asymmetry. It is considered a crucial direction for overcoming existing technological bottlenecks. However, under the condition of a fixed total driving laser energy, beam-target coupling efficiency remains one of the key bottlenecks restricting the implosion performance of hybrid drive. Existing hybrid drive schemes have failed to effectively solve this problem, resulting in difficulties in achieving substantial improvements in fusion yield.

[0006] Cross-beam energy transfer (CBET) technology, as an effective means of laser energy manipulation, has been validated in the laboratory. For example, Kirkwood et al. at LLNL Laboratory conducted a demonstration experiment on the NIF facility using plasma media generated by a gas bag target. By precisely controlling the parameters of the pump beam and signal beam, they successfully combined eight laser beams, demonstrating its feasibility in laser energy transfer. However, this technology has not yet been applied to improve beam-target coupling efficiency in hybrid-driven ICFs, nor has a complete method and system been developed, failing to address the core bottlenecks of existing hybrid-driven schemes. Summary of the Invention

[0007] To address the technical problems of low beam-target coupling efficiency, limited fusion yield, and difficulty in effectively controlling drive asymmetry in existing hybrid-driven inertial confinement fusion, this invention provides a method and system for improving beam-target coupling efficiency and fusion yield. By precisely controlling laser energy and optimizing structural parameters, both beam-target coupling efficiency and fusion yield are improved, while simultaneously increasing tolerance to drive asymmetry and suppressing drive asymmetry, thus providing technical support for the engineering application of inertial confinement fusion.

[0008] A method for improving beam-target coupling efficiency and fusion yield includes the following steps: S1: Prepare a high-Z material black cavity, wherein the black cavity is a sealed container with an open structure on the surface, and laser injection holes (LEHs) are symmetrically distributed on the surface of the black cavity; place a target pellet containing fusion fuel in the center of the black cavity, and fill the black cavity with low-density gas; the diameter of the target pellet is 1 / 10 to 1 / 5 of the diameter of the black cavity; S2: At time t1, eight or more short-pulse, high-power indirect-drive laser beams are injected into the black cavity through the laser injection hole (LEH). The pulse width of the indirect-drive laser is <20ns, and the single-beam power density is <20ns. Laser irradiation of the inner wall of the black cavity generates X-ray radiation, which initially compresses the target pellet and generates pre-plasma that expands away from the center of the black cavity. During laser injection, it is ensured that the laser does not escape from other injection holes or be blocked by the target pellet. S3: At time t2, eight or more short-pulse, high-power direct-drive lasers are aimed at the target pellet at the center of the black cavity and injected into the black cavity through the laser injection hole (LEH), where t2>t1, and the injection time of the direct-drive laser is earlier than the end time of the indirect-drive laser; energy transfer technology is used to transfer part or all of the energy of the indirect-drive laser after t2 to the direct-drive laser; the direct-drive laser continuously obtains energy from the indirect-drive laser to heat and compress the pre-plasma generated in step 2 to a high density, increase the driving pressure, and finally compress the target pellet to generate fusion neutrons; the total energy of the direct-drive laser is 0.5 to 5 times the total energy of the indirect-drive laser, and the spot size of the direct-drive laser is 0.5 to 1.2 times the diameter of the target pellet; S4: Using neutron yield measurement equipment, neutron maximum emission time measurement equipment, ion temperature measurement equipment, and hot spot imaging equipment, the number of neutrons produced by the fusion reaction, the maximum neutron emission time, the ion temperature, and the size and shape of the hot spot are measured respectively. S5: Revise the numerical simulation model based on the parameters measured in step 4, and combine the numerical simulation to adjust the black cavity size, target size, the difference between t1 and t2, and the energy conversion coefficient between the direct-driven laser and the indirect-driven laser to obtain the dependence of neutron yield on the above parameters. S6: Based on simulation predictions and experimental results, iteratively adjust the key parameters in step 5 until the experiment obtains the maximum number of neutrons, thus achieving the optimal optimization of fusion yield.

[0009] A system for improving beam-target coupling efficiency and fusion yield includes a high-Z material black cavity, an indirect-drive laser assembly, a direct-drive laser assembly, an energy transfer module, and a diagnostic measurement module. The high-Z material black cavity is a sealed container with an open structure on the surface. Laser injection holes (LEHs) are symmetrically distributed on the surface of the black cavity. A target pellet containing fusion fuel is placed in the center of the black cavity. The black cavity is filled with low-density gas. The diameter of the target pellet is 1 / 10 to 1 / 5 of the diameter of the black cavity. The indirect-drive laser assembly is used to generate eight or more short-pulse, high-power indirect-drive laser beams, with a pulse width of <20ns and a single-beam power density of <20ns. At time t1, X-rays can be injected into the black cavity through the laser injection hole (LEH) to irradiate the inner wall of the black cavity and generate X-ray radiation. The direct-drive laser assembly is used to generate eight or more short-pulse, high-power direct-drive laser beams, with a pulse width of <20ns and a single-beam power density of <20ns. At time t2 (t2>t1), the laser can be injected into the black cavity through the laser injection hole (LEH) and aimed at the target. The total energy of the directly driven laser is 0.5 to 5 times that of the indirectly driven laser, and the spot size is 0.5 to 1.2 times the diameter of the target. The energy transfer module is used to realize energy transfer between indirect-driven laser and direct-driven laser, and can transfer part or all of the indirect-driven laser energy after t2 to the direct-driven laser. The diagnostic measurement module includes a neutron yield measurement device, a neutron maximum emission time measurement device, an ion temperature measurement device, and a hot spot imaging device, which are used to measure the number of neutrons, the maximum emission time of neutrons, the ion temperature, and the size and shape of the hot spot, respectively.

[0010] Furthermore, the high-Z material includes one or more of Au, U, Ta and their compounds or alloys; the geometry of the black cavity is sphere or other shapes.

[0011] Furthermore, the low-density gas is He gas.

[0012] Furthermore, the ablation layer material of the target pellet includes one or more of Be, BeB alloy, high-density carbon, and plastic.

[0013] Furthermore, the energy transfer technology is cross-beam energy transfer (CBET) technology.

[0014] The beneficial effects of this invention are as follows: 1. Significantly improve beam-target coupling efficiency and fusion yield: This invention uses energy transfer technology to redistribute the energy of the indirect-drive laser to the direct-drive laser, which has a higher coupling efficiency. This breaks through the beam-target coupling efficiency bottleneck of the existing hybrid drive scheme. Combined with parameter iterative optimization, it can significantly improve beam-target coupling efficiency, thereby achieving a substantial increase in fusion yield and providing an effective path for the realization of high-gain fusion.

[0015] 2. Improved tolerance to drive asymmetry: This invention optimizes the drive environment by using symmetrically distributed laser injection holes (LEH), a reasonable ratio of black cavity to target size, and precise control of laser timing. This effectively improves the tolerance to drive asymmetry and reduces the impact of drive asymmetry on fusion yield.

[0016] 3. Effective suppression of driving asymmetry: This invention, through the structural design of the high-Z material black cavity, the precise control of the pre-plasma, and the application of energy transfer technology, suppresses the coupling effect of laser plasma instability (LPI) and hydrodynamic instability (HI), thereby reducing the generation of driving asymmetry, ensuring the stability of the implosion process, and further improving the efficiency of the fusion reaction.

[0017] 4. High practicality and scalability: The materials, equipment and technologies used in the method and system of this invention have good experimental feasibility. The cross-beam energy transfer (CBET) technology has been verified in the laboratory, which is convenient for subsequent engineering promotion. At the same time, the key parameters can be flexibly adjusted according to actual experimental needs, which has strong scalability and can be adapted to inertial confinement fusion devices of different scales. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1This is a schematic diagram of a method and system for improving beam-target coupling efficiency and fusion yield according to the present invention; In the figure: 1. Black cavity, 2. Laser injection hole (LEH), 3. Indirectly driven laser, 4. Directly driven laser, 5. Target pellet, 6. Neutron yield measurement device, 7. Ion temperature measurement device, 8. Neutron maximum emission time measurement device, 9. Hot spot imaging device. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] The core concept of this invention is as follows: based on the characteristic that the coupling efficiency of the direct-driven beam is higher than that of the indirect-driven beam, the energy of the indirect-driven laser within a specific time window is redistributed to the direct-driven laser through a specific energy transfer technology. Combined with the structural design of the high-Z material black cavity and the precise control of the laser timing, the beam-target coupling efficiency is improved. At the same time, through repeated iterations of experiments and numerical simulations, key parameters are optimized to further improve fusion yield.

[0022] The method of the present invention includes the following steps: Step 1: Fabrication of a high-Z material black cavity 1. The black cavity 1 is a structure formed by openings in the surface of a sealed container. Its inner wall is made of a high-Z metallic material, including but not limited to Au, U, Ta, and their compounds and alloys. High-Z materials have excellent X-ray radiation characteristics, effectively improving the conversion efficiency of laser energy to X-rays. The geometry of the black cavity 1 includes, but is not limited to, a sphere. Laser injection holes (LEHs) 2 are symmetrically distributed on the sphere to ensure symmetry of laser injection and reduce driving asymmetry. A target pellet 5 containing fusion fuel is placed at the center of the black cavity 1. The ablation layer material of the target pellet 5 includes, but is not limited to, Be, BeB alloys, high-density carbon, and plastics. The diameter of the target pellet is 1 / 10 to 1 / 5 of the diameter of the black cavity. This size ratio ensures that the target pellet 5 obtains uniform driving pressure. The black cavity 1 is filled with a low-density gas, including but not limited to He gas, to regulate the plasma environment within the black cavity 1 and suppress laser plasma instability.

[0023] Step 2: Injection and pre-compression of indirect-driven laser 3. At time t1, eight or more short-pulse, high-power indirect-driven lasers 3 are injected into the black cavity through the laser injection port (LEH) 2. The pulse width of the indirect-driven laser 3 is <20ns, and the single-beam power density is [not specified]. After the laser irradiates the inner wall of the black cavity 1, it excites the generation of X-ray radiation. The X-rays form a stable radiation field in the black cavity, which initially compresses the target pellet 5 and generates pre-plasma that expands away from the center of the black cavity. During the laser injection process, it is necessary to ensure that the laser does not pass through other injection holes and is not blocked by the target pellet 5 at the center of the black cavity 1, so as to avoid wasting laser energy and aggravating the asymmetry of the drive.

[0024] Step 3: Direct-Driven Laser Injection and Energy Transfer. At time t2, eight or more short-pulse, high-power direct-driven lasers are aimed at the target pellet 5 at the center of the black cavity 1 and injected into the black cavity through the laser injection port (LEH) 2, where t2 > t1. The injection time of the direct-driven laser 4 is earlier than the end time of the indirect-driven laser 3 to ensure continuous energy transfer. Energy transfer techniques, including but not limited to cross-beam energy transfer (CBET), are used between the direct-driven laser 4 and the indirect-driven laser 3 to transfer some or all of the energy from the indirect-driven laser after t2 to the direct-driven laser 4. During the irradiation of the target pellet 5 by the direct-driven laser 4, energy is continuously obtained from the indirect-driven laser 4. Simultaneously, the pre-plasma generated in Step 2 is heated and compressed to a high density, forming a density plateau, significantly increasing the driving pressure. Ultimately, this compresses the fusion fuel within the target pellet 5, triggering a fusion reaction and producing fusion neutrons. Among them, the total energy of the directly driven laser 4 is 0.5 to 5 times that of the indirectly driven laser 3, and the spot size is 0.5 to 1.2 times the diameter of the target pellet. This parameter range can ensure the efficient coupling between the directly driven laser and the target pellet.

[0025] Step 4: Fusion Parameter Diagnosis Measurement. The number of neutrons produced by the fusion reaction (i.e., fusion yield) is measured using the neutron yield measurement device 6, the maximum neutron emission time is measured using the maximum neutron emission time measurement device 8, the ion temperature in the fusion reaction is measured using the ion temperature measurement device 7, and the size and shape of the hot spot are measured using the hot spot imaging device 9. All of the above parameters can intuitively reflect the effect of the fusion reaction and provide data support for subsequent parameter optimization.

[0026] Step 5: Numerical Simulation and Parameter Adjustment. Based on the parameters such as neutron yield, ion temperature, and hot spot size and shape obtained in Step 4, the numerical simulation model is revised to ensure consistency between the simulation results and experimental results. Using the revised numerical simulation model, key parameters such as the size of black cavity 1 and target pellet 5, the difference between t1 and t2, and the energy conversion coefficient between directly driven laser 4 and indirectly driven laser 3 are adjusted to obtain the dependence of neutron yield on the above parameters from the simulation, clarifying the influence of each parameter on the fusion yield.

[0027] Step 6: Parameter Iterative Optimization. Based on the prediction results of numerical simulation and the actual experimental results, the key parameters in Step 5 are iteratively adjusted repeatedly to continuously optimize the experimental conditions until the combination of key parameters with the highest number of neutrons is obtained experimentally, thereby achieving the best optimization of fusion yield and ultimately achieving a dual improvement in beam-target coupling efficiency and fusion yield.

[0028] Corresponding to the above method, the present invention also provides a system for improving beam-target coupling efficiency and fusion yield, including a high-Z material black cavity 1, an indirect-drive laser component, a direct-drive laser component, an energy transfer module, and a diagnostic measurement module. These modules work together to achieve the complete execution of the above method. 1. High Z material black cavity 1: As the core carrier for the interaction between laser and target, its structure and material parameters meet the requirements in step 1, providing a stable environment for fusion reaction.

[0029] 2. Indirectly driven laser assembly: used to generate an indirectly driven laser 3 that meets the requirements of step 2. It can precisely control the laser pulse width, power density, number of beams and injection time t1 to ensure that the laser can be stably injected into the black cavity and excite X-ray radiation.

[0030] 3. Direct-drive laser assembly: used to generate a direct-drive laser 4 that meets the requirements of step 3. It can precisely control the laser's pulse width, power density, number of beams, spot size, total energy, and injection time t2 to ensure that the laser can accurately aim at the target and achieve energy coupling with the indirect-drive laser.

[0031] 4. Energy Transfer Module: The core is used to realize energy transfer between indirect-driven laser and direct-driven laser. The energy transfer technology used includes, but is not limited to, cross-beam energy transfer (CBET) technology. The energy transfer ratio can be adjusted according to experimental requirements to ensure efficient energy utilization.

[0032] 5. Diagnostic Measurement Module: Composed of neutron yield measurement device 6, neutron maximum emission time measurement device 8, ion temperature measurement device 7, and hot spot imaging device 9, it can measure various key parameters of the fusion reaction in real time and accurately, providing reliable data support for parameter optimization.

[0033] like Figure 1 As shown, the black cavity 1 is a spherical structure, and laser injection holes (LEHs) 2 are symmetrically distributed on the surface of the black cavity 1. The indirect-driven laser 3 and the direct-driven laser 4 are injected into the black cavity 1 through the laser injection holes (LEHs) 2 respectively. The target pellet 5 is located at the center of the black cavity 1, and the fusion reaction occurs in the target pellet 5. The neutron yield measurement device 6, the ion temperature measurement device 7, the neutron maximum emission time measurement device 8, and the hot spot imaging device 9 are arranged outside the black cavity 1 respectively, and are used to measure various key parameters of the fusion reaction in real time.

[0034] After the indirect-driven laser 3 is injected into the black cavity 1, it irradiates the inner wall of the black cavity 1 to generate X-ray radiation, which initially compresses the target pellet 5 and generates pre-plasma. After the direct-driven laser 4 is injected, energy transfer is achieved through the energy transfer module and the indirect-driven laser 3, continuously acquiring energy and heating and compressing the pre-plasma to form a density plateau. Under the combined action of X-ray radiation and the density plateau, the fusion fuel in the target pellet 5 undergoes a fusion reaction, generating fusion neutrons. The various devices in the diagnostic measurement module measure the fusion parameters respectively, providing data support for parameter optimization.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving beam-target coupling efficiency and fusion yield, characterized in that, Includes the following steps: S1: Prepare a high-Z material black cavity, wherein the black cavity is a sealed container with an open structure on the surface, and laser injection holes (LEHs) are symmetrically distributed on the surface of the black cavity; place a target pellet containing fusion fuel in the center of the black cavity, and fill the black cavity with low-density gas; the diameter of the target pellet is 1 / 10 to 1 / 5 of the diameter of the black cavity; S2: At time t1, eight or more short-pulse, high-power indirect-drive laser beams are injected into the black cavity through the laser injection hole (LEH). The pulse width of the indirect-drive laser is <20ns, and the single-beam power density is <20ns. Laser irradiation of the inner wall of the black cavity generates X-ray radiation, which initially compresses the target pellet and generates pre-plasma that expands away from the center of the black cavity. During laser injection, it is ensured that the laser does not escape from other injection holes or be blocked by the target pellet. S3: At time t2, eight or more short-pulse, high-power direct-drive lasers are aimed at the target pellet at the center of the black cavity and injected into the black cavity through the laser injection hole (LEH), where t2>t1, and the injection time of the direct-drive laser is earlier than the end time of the indirect-drive laser; energy transfer technology is used to transfer part or all of the energy of the indirect-drive laser after t2 to the direct-drive laser; the direct-drive laser continuously obtains energy from the indirect-drive laser to heat and compress the pre-plasma generated in step 2 to a high density, increase the driving pressure, and finally compress the target pellet to generate fusion neutrons; the total energy of the direct-drive laser is 0.5 to 5 times the total energy of the indirect-drive laser, and the spot size of the direct-drive laser is 0.5 to 1.2 times the diameter of the target pellet; S4: Using neutron yield measurement equipment, neutron maximum emission time measurement equipment, ion temperature measurement equipment, and hot spot imaging equipment, the number of neutrons produced by the fusion reaction, the maximum neutron emission time, the ion temperature, and the size and shape of the hot spot are measured respectively. S5: Revise the numerical simulation model based on the parameters measured in step 4, and combine the numerical simulation to adjust the black cavity size, target size, the difference between t1 and t2, and the energy conversion coefficient between the direct-driven laser and the indirect-driven laser to obtain the dependence of neutron yield on the above parameters. S6: Based on simulation predictions and experimental results, iteratively adjust the key parameters in step 5 until the experiment obtains the maximum number of neutrons, thus achieving the optimal optimization of fusion yield.

2. A system for improving beam-target coupling efficiency and fusion yield, characterized in that, The method for implementing any one of claims 1-3 includes a black cavity assembly, an indirect-drive laser assembly, a direct-drive laser assembly, an energy transfer module, and a diagnostic measurement module; The black cavity assembly is a black cavity made of high Z material. The black cavity is a sealed container with an open structure on the surface. Laser injection holes (LEH) are symmetrically distributed on the surface of the black cavity. A target pellet containing fusion fuel is placed in the center of the black cavity. The black cavity is filled with low-density gas. The diameter of the target pellet is 1 / 10 to 1 / 5 of the diameter of the black cavity. The indirect-drive laser assembly is used to generate eight or more short-pulse, high-power indirect-drive laser beams, with a pulse width of <20ns and a single-beam power density of <20ns. At time t1, X-rays can be injected into the black cavity through the laser injection hole (LEH) to irradiate the inner wall of the black cavity and generate X-ray radiation. The direct-drive laser assembly is used to generate eight or more short-pulse, high-power direct-drive laser beams, with a pulse width of <20ns and a single-beam power density of <20ns. At time t2 (t2>t1), the laser can be injected into the black cavity through the laser injection hole (LEH) and aimed at the target. The total energy of the directly driven laser is 0.5 to 5 times that of the indirectly driven laser, and the spot size is 0.5 to 1.2 times the diameter of the target. The energy transfer module is used to realize energy transfer between indirect-driven laser and direct-driven laser, and can transfer part or all of the indirect-driven laser energy after t2 to the direct-driven laser. The diagnostic measurement module includes a neutron yield measurement device, a neutron maximum emission time measurement device, an ion temperature measurement device, and a hot spot imaging device, which are used to measure the number of neutrons, the maximum emission time of neutrons, the ion temperature, and the size and shape of the hot spot, respectively.

3. The method according to claim 1 or the system according to claim 2, characterized in that, The high-Z material includes one or more of Au, U, Ta and their compounds or alloys; the geometry of the black cavity is sphere or other shapes.

4. The method according to claim 1 or the system according to claim 2, characterized in that, The low-density gas is He gas.

5. The method according to claim 1 or the system according to claim 2, characterized in that, The ablation layer material of the target pellet includes one or more of Be, BeB alloy, high-density carbon, and plastic.

6. The method according to claim 1 or the system according to claim 2, characterized in that, The energy transfer technology is Cross-Beam Energy Transfer (CBET).

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