JP7519681B2 - Fuel pellets, fuel pellet manufacturing method, nuclear fusion reactor, and nuclear fusion method - Google Patents

Description

The present invention relates to fuel pellets, a method for manufacturing fuel pellets, a nuclear fusion reactor, and a nuclear fusion method.

Laser fusion is known in the past, in which a laser is irradiated onto a fusion fuel, causing the fusion fuel to ignite. A deuterium-tritium mixture (hereinafter referred to as DT) is typically used as the fusion fuel. A central ignition method has been proposed as a method for this type of laser fusion.

The central ignition method is a method in which a laser beam is directed at a spherical fuel pellet to implode the fuel pellet, forming a fusion ignition part (hot spark) in the center, causing ignition and combustion of the fuel. For example, Patent Document 1 discloses a power generation method and a fusion reactor in which a fusion flame is generated (by the central ignition method) by a fusion laser pulse having a pulse duration of less than 10 ps and a power of more than 1 petawatt.

Meanwhile, in the 1990s, the fast ignition technique was invented, developing from central ignition. Fast ignition is a technique in which, like central ignition, fuel is imploded, and then the fuel is heated with a short-pulse, high-intensity laser or similar to cause ignition and combustion. With this technique, the hot spark is created by a separate heat source, which relaxes the technical requirements for implosion.

JP 2017-513018 A

To perform the central ignition type laser nuclear fusion described above, it is necessary to manufacture fuel pellets that have a spherical shell-shaped solid fuel layer with fuel gas sealed inside. In other words, the fuel pellets need to have a hollow structure.

In addition, in the central ignition method, the fuel pellets must be imploded spherically symmetrically. Therefore, the surface irregularities of the solid fuel layer must be kept to the order of nm, and the thickness unevenness of the solid fuel layer must be kept to 0.1% or less. Furthermore, in order to solidify DT, it must be cooled to 18K or less. Therefore, when using DT as a fusion fuel, a technology is required to solidify DT very slowly and grow the solid DT crystals in order to form a solid DT layer of uniform thickness. Typically, it takes about 24 hours from the start of filling DT fuel to the production of fuel pellets.

As such, conventional fuel pellet manufacturing methods require extremely high manufacturing precision. This makes it difficult to mass-produce fuel pellets.

One aspect of the present invention was made in consideration of the above problems, and its purpose is to provide fuel pellets that can be mass-produced and a method for manufacturing fuel pellets.

In order to solve the above problems, a fuel pellet according to one aspect of the present invention is a fuel pellet used in inertial fusion, in which a fusion reaction occurs by irradiating a fusion fuel with a laser, and is characterized in that it comprises the fusion fuel and a spherical shell-shaped membrane that contains the fusion fuel, and the fusion fuel fills the membrane in a liquid or solid state.

The fusion fuel may be liquid. The fusion fuel may be solid. The membrane may be made of plastic.

The fuel pellet may also have a conical shape and further include a guide member that guides the laser from the bottom side to the apex side of the cone shape, the membrane may have a through hole, and the apex side of the cone shape of the guide member may be inserted into the through hole.

In order to solve the above problems, a fuel pellet according to one aspect of the present invention is a fuel pellet used in inertial fusion, in which a fusion reaction occurs by irradiating a fusion fuel with a laser, and is characterized in that it comprises the fusion fuel and a spherical foam having a plurality of pores that contain the fusion fuel within the pores.

In order to solve the above problems, a method for manufacturing fuel pellets according to one aspect of the present invention includes a supply step of supplying a plurality of the films into a chamber, a depressurization step of reducing the pressure in the chamber to a predetermined degree of vacuum, and a filling step of filling the films with fusion fuel in the chamber at the predetermined degree of vacuum.

In order to solve the above problems, a method for manufacturing fuel pellets according to one aspect of the present invention includes a supply step of supplying a plurality of the foam bodies into a chamber, a depressurization step of depressurizing the chamber to a predetermined degree of vacuum, and a filling step of filling the foam bodies with the fusion fuel in the chamber at the predetermined degree of vacuum.

To solve the above problems, a nuclear fusion reactor according to one aspect of the present invention is characterized by using the above-mentioned fuel pellets.

To solve the above problems, a nuclear fusion method according to one aspect of the present invention is characterized in that the fuel pellets are irradiated with an implosion laser and a heating laser.

According to one aspect of the present invention, it is possible to provide fuel pellets that can be mass-produced and a method for manufacturing fuel pellets.

FIG. 1 illustrates a method for igniting fusion fuel using a central ignition system. FIG. 1 illustrates a method for igniting fusion fuel using fast ignition. 1 is a schematic cross-sectional view of a fuel pellet according to an embodiment of the present invention; FIG. 2 is a diagram showing a method of igniting nuclear fusion fuel by a fast ignition method using the fuel pellets. FIG. 2 is a schematic diagram of a nuclear fusion reactor in which the fuel pellets are irradiated with a laser. 3 is a process diagram showing a method for producing the fuel pellets. FIG. 3 is a schematic diagram showing the fuel pellet manufacturing apparatus in a supply step and a depressurization step. FIG. FIG. 2 is a schematic diagram showing the fuel pellet manufacturing apparatus in the filling step. FIG. 2 is a schematic diagram showing the fuel pellet manufacturing apparatus in the continuous injection step. FIG. 4 is a schematic cross-sectional view of a fuel pellet according to another embodiment of the present invention. FIG. 11 is a schematic cross-sectional view of a fuel pellet according to still another embodiment of the present invention. 1 is a graph showing the relationship between the power of an implosion laser and a value indicative of compression of the fusion fuel. FIG. 2 is a diagram showing a pulse waveform of the implosion laser. 1 is a graph showing the fusion energy output for each laser wavelength of the heating laser. 1 is a table showing the electron energy required for a nuclear fusion reaction and the power of the heating laser corresponding to each laser wavelength of the heating laser.

[Embodiment 1]
(Features of one aspect of the present invention)
Fig. 1 is a diagram showing a method for igniting nuclear fusion fuel using a central ignition method. Fig. 2 is a diagram showing a method for igniting nuclear fusion fuel using a fast ignition method. With reference to Figs. 1 and 2, a method for igniting nuclear fusion fuel using a hollow fuel pellet will be described.

In the central ignition method, as shown by reference symbol 1A in FIG. 1, the fuel pellet 110 comprises a spherical solid fuel layer 111 and an ablator layer 112 provided on its outer periphery. In addition, fuel gas 113 is sealed inside the solid fuel layer 111. The ablator layer 112 is, for example, a capsule made of plastic.

As shown by reference symbol 1B in FIG. 1, by irradiating the fuel pellets 110 with an implosion laser 115, the spherical solid fuel layer 111 is compressed spherically symmetrically. Specifically, the ablator layer 112 is instantly transformed into high-temperature plasma 112a by irradiation with the implosion laser 115, and expands outward from the fuel pellets 110. This outward expansion causes a sudden pressure to be applied to the solid fuel layer 111 inward. In other words, the fuel pellets 110 are imploded.

As shown by reference symbol 1C in FIG. 1, the imploded solid fuel layer 111 is compressed to a density several thousand times that before compression at the time of maximum compression, and becomes the main fuel portion 111a. The fuel gas 113 is heated by the compression of the solid fuel layer 111, forming a hot spark 113a. The hot spark 113a is a region where a nuclear fusion reaction is induced and neutrons and alpha particles are generated. Within the hot spark 113a, the unreacted fuel is heated by alpha particles generated by the nuclear fusion reaction of some of the fuel, promoting the nuclear fusion reaction. In other words, the fuel pellets 110 ignite.

As shown by reference symbol 1D in FIG. 1, the nuclear fusion ignition of the hot spark 113a causes the surrounding main fuel section 111a to be heated by α particles. This causes the nuclear fusion reaction to begin suddenly in the main fuel section 111a as well. In other words, the fuel pellets 110 burn.

In such a central ignition method, disturbances may occur at the interface between the main fuel section 111a and the hot spark 113a during implosion. To suppress such disturbances, the central ignition method requires extremely high uniformity in the compression of the solid fuel layer 111. Specifically, the unevenness of the surface of the solid fuel layer 111 must be suppressed to the order of nm. In addition, the unevenness of the thickness of the solid fuel layer 111 must be suppressed to 0.1% or less.

In addition, in the central ignition method, it is necessary to form a hot spark 113a by implosion. Therefore, in the manufacturing process of the fuel pellet 110, it is necessary to seal the fuel gas 113 inside the solid fuel layer 111. In other words, in the fuel pellet 110, the solid fuel layer 111 needs to have a hollow structure inside the ablator layer 112.

On the other hand, in the fast ignition method, as shown by reference symbol 2C in FIG. 2, a heating laser 116 is irradiated onto the main fuel section 111a to form a hot spark 113a in the center of the main fuel section 111a. As shown by reference symbols 2A, 2B, and 2D in FIG. 2, the process in the fast ignition method other than the nuclear fusion heating of the fuel pellets 110 is the same as in the central ignition method.

In this type of fast ignition method, hot sparks 113a are formed by forcibly heating from the outside using a heating laser 116. In other words, in the fast ignition method, it is not necessary to form hot sparks 113a by implosion. Therefore, compared to the central ignition method, there is no need to consider disturbance of the interface between the main fuel part 111a and the hot spark 113a during implosion, and the conditions for ensuring uniform compression of the solid fuel layer 111 are relaxed.

The inventors have discovered that by using fuel pellets with a solid structure in laser fusion using the fast ignition method, it is possible to achieve ignition and combustion of fusion fuel. Furthermore, the inventors have discovered that by making the fuel pellets solid, it is possible to easily mass-produce fuel pellets using the manufacturing method described below (see Figures 5 to 8). These findings are highly unexpected and could not be predicted from conventional wisdom that a hollow fuel pellet structure is essential to achieve ignition and combustion of fusion fuel.

(Configuration of the fuel pellet 10)
Fig. 3 is a schematic cross-sectional view of a fuel pellet 10 according to the first embodiment of the present invention. The fuel pellet 10 includes a fusion fuel 11 and a capsule (membrane) 12 that contains the fusion fuel 11. The configuration of the fuel pellet 10 having a solid structure used in laser fusion by fast ignition will be described below with reference to Fig. 3.

The fusion fuel 11 is a fuel for laser fusion (inertial fusion) in which a fusion reaction occurs by irradiating a laser. The fusion fuel 11 is, for example, a liquid. An example of the liquid is liquid DT (a mixture of deuterium and tritium). In this case, DT is cooled to about 20K and liquefied to use. Note that the fusion fuel 11 is not limited to this. The fusion fuel 11 may be a solid. An example of the solid is solid DT. Also, the fusion reaction is not limited to DT fusion. The fusion fuel 11 may be a fuel composed only of deuterium, a fuel composed only of tritium, a solid LiD (lithium deuterium) fuel, or a liquid B ₂ H ₆ (diborane) fuel, etc.

The capsule 12 is a spherical shell-shaped member that suppresses the evaporation of the fusion fuel 11. The capsule 12 is made of a material that can sufficiently suppress the evaporation of the fusion fuel 11 for about 100 ms between the injection by the fuel pellet injection mechanism 54 (see Figures 7 to 9) described below and the laser irradiation. The capsule 12 is, for example, plastic. Examples of plastic include polystyrene and polyimide. However, the capsule 12 is not limited to these. The capsule 12 may be made of glow discharge polymer, glass, carbon, or the like.

When liquid DT fuel is used as the fusion fuel 11, the outer diameter of the capsule 12 is preferably 200 to 500 μm. The thickness of the capsule 12 is set to a thickness that can sufficiently suppress the evaporation of the fusion fuel 11 and does not excessively reduce the intensity of the laser irradiated to the fusion fuel 11. Specifically, the thickness of the capsule 12 is preferably 7 μm or more and 50 μm or less, and can be, for example, about 10 μm.

The fusion fuel 11 fills the inside of the capsule 12 in a liquid or solid state. In other words, the fusion fuel 11 has a solid structure inside the capsule 12. Here, when liquid DT fuel is used as the fusion fuel 11, the fusion fuel 11 can be easily filled into the capsule 12 in a solid and iso-dense manner (at uniform density).

Figure 4 is a diagram showing a method of igniting fusion fuel 11 by a fast ignition method using fuel pellets 10. As shown by reference numeral 4A in Figure 4, an implosion laser 5 is irradiated onto the fuel pellets 10. The irradiation conditions of the implosion laser 5 will be described later with reference to Figures 12 and 13.

As shown by reference symbol 4B in FIG. 4, the capsule 12 instantly becomes a high-temperature plasma 12a upon irradiation with the implosion laser 5, and expands toward the outside of the fuel pellets 10. The expansion of this high-temperature plasma 12a causes the fusion fuel 11 to implode.

As shown by reference symbol 4C in FIG. 4, the imploded fusion fuel 11 is compressed to a density several thousand times that of the fuel before compression at the time of maximum compression, and becomes the main fuel section 11a. A heating laser 6 is irradiated onto the main fuel section 11a, forming a hot spark 13 in the center of the main fuel section 11a.

As shown by reference symbol 4D in FIG. 4, the nuclear fusion reaction is rapidly initiated in the main fuel section 111a by the nuclear fusion ignition of the hot spark 13.

(Configuration of Nuclear Fusion Reactor 1)
Fig. 5 is a schematic diagram of a fusion reactor 1 that irradiates a laser onto a fuel pellet 10. As shown in Fig. 5, the fusion reactor 1 includes an inlet 2 for the fuel pellets 10, a vacuum chamber 3, and a plurality of lenses 4. In addition, a flow path (not shown) for a coolant is provided around the vacuum chamber 3.

The fuel pellets 10 are introduced from the inlet 2 to a predetermined position in the vacuum chamber 3. Specifically, the fuel pellets 10 are introduced so that they pass through a predetermined position in the vacuum chamber 3. A plurality of lenses 4 focus the lasers 5, 6 (implosion laser 5 or heating laser 6) at a predetermined position in the vacuum chamber 3. By matching the timing at which the fuel pellets 10 pass through the predetermined position with the timing at which the lasers 5, 6 are irradiated, the lasers 5, 6 are irradiated onto the fuel pellets 10 at the predetermined position, and a nuclear fusion reaction occurs. The thermal energy generated by the nuclear fusion reaction is converted into power generation energy via a coolant by a known method.

(Method of Manufacturing Fuel Pellets 10)
FIG. 6 is a process diagram showing the manufacturing method of the fuel pellets 10. FIG. 7 is a schematic diagram showing the manufacturing device 50 of the fuel pellets 10 in the supply step S1 and the depressurization step S2. FIG. 8 is a schematic diagram showing the manufacturing device 50 of the fuel pellets 10 in the filling step S3. FIG. 9 is a schematic diagram showing the manufacturing device 50 of the fuel pellets 10 in the continuous injection step. As an example of the manufacturing method of the fuel pellets 10, a manufacturing method in which the liquid DT fuel (nuclear fusion fuel) 11 is filled into the capsule 12 will be described below with reference to FIGS. 6 to 9. Note that the manufacturing method of the fuel pellets 10 in this embodiment can be applied even when the capsule 12 is filled with a liquid fuel other than the liquid DT fuel (for example, liquid B ₂ H ₆ fuel) as the nuclear fusion fuel 11.

As shown in Figures 7 to 9, the manufacturing apparatus 50 includes a chamber 51, a vacuum pump 52, a fuel storage section 53, and a fuel pellet injection mechanism 54. The manufacturing apparatus 50 fills multiple capsules 12 with liquid DT fuel 11 to manufacture fuel pellets 10. The manufacturing apparatus 50 also supplies the fuel pellets 10 to the fusion reactor 1.

The chamber 51 is a container that stores multiple capsules 12. The chamber 51 includes a substantially cylindrical main body 511 and an ejection section 512 that is provided at the bottom of the main body 511 and has a smaller inner diameter than the main body 511. The inner diameter of the main body 511 gradually decreases downward in order to guide the multiple capsules 12 to the ejection section 512. The inner diameter of the ejection section 512 is larger than the outer diameter of the capsules 12.

The vacuum pump 52 is a pump that creates a vacuum inside the chamber 51. The fuel storage unit 53 is a tank that stores the liquid DT fuel 11 that is filled into the capsule 12. The vacuum pump 52 and the fuel storage unit 53 are each connected to the chamber 51. A valve 531 is provided between the fuel storage unit 53 and the chamber 51 to control the flow of the liquid DT fuel 11 between the fuel storage unit 53 and the chamber 51.

The fuel pellet injection mechanism 54 injects the fuel pellets 10 located at the lower end of the injection section 512 into the fusion reactor 1. Specifically, the fuel pellet injection mechanism 54 injects compressed deuterium gas onto the fuel pellets 10 located at the lower end of the injection section 512. The lower part of the injection section 512 and the inlet 2 of the fusion reactor 1 are connected by a pipe (not shown). The fuel pellets 10 are injected into the fusion reactor 1 through the pipe by the pressure of the compressed deuterium gas.

The manufacturing method of the fuel pellets 10 in this embodiment is as follows. First, as shown in FIG. 7, a plurality of capsules 12 are supplied into the chamber 51 from an inlet (not shown) provided in the chamber 51 (S1 in FIG. 6).

Next, the vacuum pump 52 reduces the pressure inside the chamber 51 (S2 in FIG. 6). The vacuum pump 52 creates a predetermined degree of vacuum inside the chamber 51.

Next, as shown in FIG. 8, liquid DT fuel 11 is filled into multiple capsules 12 in chamber 51, which is at a predetermined vacuum level (S3 in FIG. 6). Specifically, liquid DT fuel 11 stored in fuel storage section 53 is supplied to chamber 51 by adjusting valve 531. Here, capsules 12 are permeable to liquid DT fuel 11. Therefore, the liquid DT fuel 11 supplied to chamber 51 is filled into multiple capsules 12. By the above manufacturing method (S1 to S3 in FIG. 6), fuel pellets 10 in which capsules 12 are filled with liquid DT fuel 11 can be manufactured.

The manufacturing device 50 supplies the fuel pellets 10 manufactured by S1 to S3 in FIG. 6 to the fusion reactor 1. Specifically, first, the valve 531 is adjusted to recover the liquid DT fuel 11 remaining in the chamber 51 to the fuel storage section 53 as shown in FIG. 9. Next, compressed deuterium gas is injected from the nozzle of the fuel pellet injection mechanism 54 to the fuel pellets 10 located at the bottom of the injection section 512. This ejects the fuel pellets 10 into the fusion reactor 1. This operation is repeated to eject multiple fuel pellets 10 in the chamber 51 continuously into the fusion reactor 1. Note that the method of supplying the fuel pellets 10 to the fusion reactor 1 is not limited to this, and for example, the fuel pellets 10 may be supplied to the fusion reactor 1 by allowing them to fall freely.

This method of manufacturing fuel pellets 10 dramatically improves production efficiency compared to conventional fuel pellet manufacturing methods because it does not require technology to grow solid DT crystals. Therefore, mass production of fuel pellets 10 can be easily achieved. In addition, this method of supplying fuel pellets 10 can sufficiently suppress the evaporation of fusion fuel 11 between the time of injection by the fuel pellet injection mechanism 54 and the time of laser irradiation.

Also, before the fuel pellets 10 are supplied to the fusion reactor 1, the liquid DT fuel 11 may be cooled and solidified to form solid DT fuel. This prevents the fusion fuel 11 from evaporating between the time of injection by the fuel pellet injection mechanism 54 and the time of laser irradiation. Therefore, the fuel pellets 10 can retain the solid DT fuel for a long period of time.

[Embodiment 2]
(Configuration and manufacturing method of fuel pellets 20)
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

Figure 10 is a schematic cross-sectional view of a fuel pellet 20 according to embodiment 2 of the present invention. The fuel pellet 20 includes a fusion fuel 11, a capsule (membrane) 22, and a cone (induction member) 23.

Capsule 22 differs from capsule 12 in that it has a through hole 22a formed by a circular cutting process. For example, for a capsule 22 having an outer diameter of 500 μm, a through hole 22a having an inner diameter of 150 μm is formed. The through hole 22a is formed, for example, by a femtosecond laser device that executes a circular cutting program. This improves the reproducibility of the circular cutting process of capsule 22, making it possible to mass-produce capsules 22.

The cone 23 has a conical shape and is a guide member that guides the heating laser 6 from the bottom side of the cone shape to the apex 23a side. The cone 23 is joined to the capsule 22 so that the apex 23a side is inserted into the through hole 22a. The cone 23 is made of a relatively heavy metal such as gold or aluminum.

At the time of implosion, the compressed fusion fuel 11 is surrounded by plasma with a density higher than the cutoff density for the laser. Therefore, it is difficult to propagate the heating laser 6 into the inside of the fusion fuel 11 by simply irradiating the periphery of the fusion fuel 11 with the heating laser 6. Therefore, the heating laser 6 is irradiated to the apex 23a through the inside of the cone 23. This generates high-energy electrons inside the capsule 22, and a hot spark can be formed.

The manufacturing method of the fuel pellets 20 is the same as that of the fuel pellets 10. When manufacturing the fuel pellets 20, the direction of the cone 23 is appropriately controlled so that the fusion fuel 11 does not get inside the cone 23. When ejecting the fuel pellets 20 into the fusion reactor 1, the attitude of the fuel pellets 20 is appropriately controlled so that the heating laser 6 is irradiated onto the cone 23.

[Embodiment 3]
(Configuration and manufacturing method of fuel pellets 30)
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

Figure 11 is a schematic cross-sectional view of a fuel pellet 30 according to a third embodiment of the present invention. As shown in Figure 11, the fuel pellet 30 includes a fusion fuel 11, a capsule 12, and a foam 33.

The foam 33 has a plurality of pores 33a, and contains the fusion fuel 11 in the pores 33a. The foam 33 has a solid structure inside the capsule 12. Note that the fuel pellet 30 does not necessarily have to include the capsule 12. In other words, the fuel pellet 30 may include the fusion fuel 11 and a spherical foam 33 that contains the fusion fuel 11 in the pores 33a.

The material of the foam 33 is, for example, a mixture of resorcinol-formalin (RF) and phloroglucinol carboxylic acid-formalin (PF) (RF-PF). However, the material of the foam 33 is not limited to this.

The fuel pellets 30 can prevent air layers from remaining in the fuel pellets 30 by storing the fusion fuel 11 in the pores 33a of the form 33. In other words, the fusion fuel 11 can be packed solidly and evenly in the pores 33a of the form 33. In particular, when the liquid DT fuel 11 is cooled and solidified to become solid DT fuel, the entire form 33 is compressed in accordance with the reduction in volume caused by the solidification of the DT. Therefore, even when solid DT fuel is used, the fusion fuel 11 can be packed solidly and evenly in the same manner. The manufacturing method of the fuel pellets 30 is the same as the manufacturing method of the fuel pellets 10.

[Embodiment 4]
(Manufacturing method when using solid LiD fuel)
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

In this embodiment, a manufacturing method for filling solid LiD fuel into a capsule 12 will be described below as an example of a manufacturing method for fuel pellets 10.

LiD is a solid crystal at room temperature, and is usually mass-produced in powder form. Solid LiD fuel may be produced by processing solid crystalline LiD into a spherical shape. Solid LiD fuel may also be produced by bonding together a pair of hemispherical capsules filled with powdered LiD. Solid crystalline LiOD (lithium deuterium hydroxide), which is more stable than solid crystalline LiD, may also be used. However, from the viewpoint of the efficiency of power generation energy, it is more preferable to use solid crystalline LiD.

[Embodiment 5]
Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

(Laser fusion simulation)
A simulation was performed on laser nuclear fusion that occurs by irradiating the above-mentioned nuclear fusion fuel 11 with the implosion laser 5 and the heating laser 6. In this embodiment, the irradiation conditions of the implosion laser 5 and the heating laser 6 and the simulation results corresponding to the irradiation conditions will be described.

In this simulation, the peak intensity of the implosion laser 5 was set to 5×10^14 W/cm ^2. The pulse width of the implosion laser 5 was set to 60 ns. The wavelength of the implosion laser 5 was set to 0.35 μm. The spot size of the implosion laser 5 was 900 μm (the radius of the fusion fuel 11 before implosion). The peak intensity of the heating laser 6 was set to 10^20-10^21 W/cm ^2. The pulse width of the heating laser 6 was set to 20 ps. The wavelength of the heating laser 6 was set to 0.53 μm. The spot size of the heating laser 6 was 40-100 μm (approximately the radius of the fusion fuel 11 after implosion).

12 is a graph showing the relationship between the power of the implosion laser 5 and a value indicating the compression of the fusion fuel 11. In the graph of FIG. 12, the vertical axis represents the fuel density radial product ρR (g/cm ² ) after implosion by the implosion laser 5, and the horizontal axis represents the power output Eimp (kJ) of the implosion laser 5.

By simulating laser nuclear fusion, the inventors have confirmed that when the output Eimp of the implosion laser 5 is set to 10 kJ, ρR=0.5 g/ ^cm2 is achieved, and the nuclear fusion reaction turns into a chain reaction (corresponding to point A in FIG. 12). In addition, the inventors have confirmed that when the output Eimp of the implosion laser 5 is set to 500 kJ, ρR=2.4 g/ ^cm2 is achieved, and power can be generated by the nuclear fusion reaction (corresponding to point B in FIG. 12). In addition, these simulation results are consistent with theoretical calculation results that the output Eimp of the implosion laser 5 and the fuel density radius product ρR after implosion have a linear relationship like the straight line in FIG. 12.

In conventional laser fusion methods using hollow fusion fuel, the output of the implosion laser required to achieve ρR at which electricity can be generated by fusion reactions is 5 MJ. On the other hand, in laser fusion methods using solid fusion fuel 11, the output of the implosion laser required to achieve ρR at which electricity can be generated by fusion reactions is 500 kJ. In other words, compared to conventional laser fusion methods, the output of the implosion laser 5 can be reduced to about 1/10 in laser fusion methods using solid fusion fuel 11.

Fig. 13 is a graph showing the pulse waveform of the implosion laser 5. In the graph of Fig. 13, the vertical axis represents the intensity (W/ ^cm2 ) of the implosion laser 5, and the horizontal axis represents the elapsed time (ns) from the start of irradiation of the implosion laser 5. The dashed line represents the pulse waveform of the implosion laser 5 irradiating the fuel pellet 10 without the cone 23, and the solid line represents the pulse waveform of the implosion laser 5 irradiating the fuel pellet 20 with the cone 23.

As shown in FIG. 13, the pulse waveform of the implosion laser 5 irradiated to the solid fusion fuel 11 is set to increase in intensity in stages. For example, in the case of a fuel pellet 10 without a cone 23, the intensity of the implosion laser 5 is increased in stages at 0 ns, 10 ns, 12 ns, 13 ns, and 13.5 ns from the start of irradiation by the implosion laser 5, generating a total of five shock waves. In addition, these five shock waves are designed to reach the center of the fusion fuel 11 simultaneously. As a result, the five shock waves overlap, realizing extremely high pressure on the solid fusion fuel 11. The pressure compresses the fusion fuel 11 to a high density. The high density state of the fusion fuel 11 continues for a period of about 100 ps. During that period, the heating laser 6 is irradiated to the fusion fuel 11 to form a hot spark.

Figure 14 is a graph showing the energy output of nuclear fusion corresponding to each laser wavelength λL (λL = 0.35 μm, 0.53 μm, 1.05 μm) of the heating laser 6. Figure 15 is a table showing the electron energy required for nuclear fusion reaction and the output of the heating laser 6 corresponding to each laser wavelength λL of the heating laser 6. In the graph of Figure 14, the vertical axis represents the energy output of nuclear fusion EF (MJ), and the horizontal axis represents the energy Eb (kJ) of the electrons generated by the heating laser 6.

As shown in FIG. 14, when the electron energy Eb exceeds a certain threshold, nuclear fusion ignition occurs and the nuclear fusion energy output EF rises rapidly (several hundred times). Furthermore, this specific threshold of the electron energy Eb varies depending on the laser wavelength λL of the heating laser 6. When λL=0.35 μm, 0.53 μm, and 1.05 μm, the specific threshold of the electron energy Eb is 30 kJ, 35 kJ, and 50 kJ, respectively. That is, when λL=0.35 μm, 0.53 μm, and 1.05 μm, the electron energy Eb required for the nuclear fusion reaction is 30 kJ, 35 kJ, and 50 kJ, respectively (see also FIG. 15).

The output of the heating laser 6 to achieve the electron energy Eb required for a nuclear fusion reaction varies depending on the conversion efficiency from the heating laser 6 to electrons. Assuming that the conversion efficiency from the heating laser 6 to electrons is 40%, as shown in FIG. 15, when λL = 0.35 μm, 0.53 μm, and 1.05 μm, the output of the heating laser 6 required for a nuclear fusion reaction is 75 kJ, 87.5 kJ, and 125 kJ, respectively. In addition, the conversion efficiency from the heating laser 6 to electrons varies depending on the divergence angle of the electrons. Therefore, the output of the heating laser 6 required for a nuclear fusion reaction is determined by the wavelength λL of the heating laser 6 and the divergence angle of the electrons.

(Additional Notes)
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

For example, in the above embodiment, the manufacturing method of the present invention is applied to fuel pellets used in inertial confinement fusion, but is not limited to this. For example, the manufacturing method of the present invention may be applied to fuel pellets used in magnetic field fusion. Also, the manufacturing method of the present invention may be applied to a continuously driven target used to generate X-rays, neutrons, or EUV.

5, 115 Implosion laser 6, 116 Heating laser 10, 20, 30 Fuel pellet 11 Fusion fuel (liquid DT fuel)
12, 22 Capsule (membrane)
22a Through hole 23 Cone (guiding member)
23a apex 33 foam
33a Pore

Claims (9)

A method for producing fuel pellets to be continuously injected into a nuclear fusion reactor , comprising the steps of:
The method includes a supply step of supplying a plurality of spherical shell-shaped membranes into a chamber, a depressurization step of depressurizing the chamber to a predetermined vacuum level, and a filling step of producing a plurality of fuel pellets by filling the membranes with fusion fuel in the chamber at the predetermined vacuum level,
The fuel pellets are fuel pellets used for inertial fusion, in which a fusion reaction is caused by irradiating a fusion fuel with a laser, and the fuel pellets comprise a spherical shell-shaped membrane that contains the fusion fuel, and the fusion fuel fills the membrane in a liquid or solid state. The method for producing fuel pellets according to claim 1, characterized in that the fusion fuel is liquid. The method for producing fuel pellets according to claim 1, characterized in that the fusion fuel is solid. The method for manufacturing fuel pellets according to any one of claims 1 to 3, characterized in that the membrane is made of plastic. The fuel pellet has a conical shape and further includes a guide member that guides the laser from a bottom side to a top side of the cone shape.
The membrane has a through hole,
The method for producing fuel pellets according to claim 1 , wherein an apex side of the cone shape of the guide member is inserted into the through hole. A fuel pellet for use in inertial fusion in which a fusion reaction occurs by irradiating a fusion fuel with a laser,
the fusion fuel;
a spherical foam having a plurality of pores and containing the fusion fuel within the pores;
A fuel pellet, characterized in that the fusion fuel fills the pores in a liquid or solid state, and the foam has a solid structure. A method for producing fuel pellets according to claim 6, comprising the steps of:
A method for manufacturing fuel pellets, comprising: a supplying step of supplying a plurality of the foam bodies into a chamber; a depressurizing step of reducing the pressure inside the chamber to a predetermined vacuum level; and a filling step of filling the foam bodies with the fusion fuel inside the chamber at the predetermined vacuum level. A nuclear fusion reactor using the fuel pellets described in claim 6. A nuclear fusion method in which the fuel pellets described in claim 6 are irradiated with an implosion laser and a heating laser.

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