Preparation method of deuterium ice shell layer in millimeter scale microspheres

Abstract

The application discloses a preparation method of a deuterium ice shell layer in a millimeter-scale microsphere, and is based on a frozen target device to realize that a target pellet is hung in the center of a sleeve of the frozen target device through a deuterium gas inflation pipe, gaseous deuterium in the target pellet is converted into liquid deuterium and then into polycrystalline solid deuterium through temperature and pressure control, a temperature gradient is applied to upper and lower silicon cooling arms to sublimate and desublimate polycrystalline solid deuterium in the southern hemisphere of the target pellet to the northern hemisphere to form a relatively uniform deuterium ice layer, and the temperature of the upper and lower silicon cooling arms is simultaneously increased to the melting point temperature of the deuterium ice layer to form a deuterium layer coexisting with solid and liquid on the inner surface of the target pellet. The method can form a smooth, uniform and high-quality deuterium layer coexisting with solid and liquid in the target pellet, the average thickness of the obtained deuterium layer is 35.9 microns, the thickness PV value is 4.02 microns, and the inner surface roughness is 1.0 micron, so that the uniformity and smoothness of the deuterium layer in the target pellet are greatly improved.

Description

Technical Field

[0001] This invention relates to a method for preparing a deuterium ice shell layer inside millimeter-scale microspheres. Background Technology

[0002] Inertial confinement fusion (ICF) indirectly drives a cryogenic target with a pellet suspended at the center of a black cavity. The pellet contains cryogenically frozen fuel. A high-intensity laser beam passes through a laser entrance aperture and strikes the inner wall of the black cavity, converting the laser beam into X-rays to irradiate the pellet. The pellet implodes, compressing and heating the fuel ice layer to certain conditions to achieve thermonuclear fusion. To obtain sufficient fusion energy, the initial fuel ice layer needs to be sufficiently homogeneous and smooth to minimize Rayleigh-Taylor instabilities during ice compression. As laser inertial confinement fusion continues to advance, more and more implosion physics decomposition experiments need to be conducted. However, if all experiments are conducted using deuterium-tritium fuel, the radioactivity of tritium would bring enormous operational costs and potential threats to the environment and personnel. Therefore, using non-radioactive deuterium-tritium fuel for physics experiments is extremely necessary. However, deuterium-tritium does not produce beta decay heat and cannot undergo self-homogenization. Researchers have long invested significant resources in studying homogenization techniques that do not contain tritium fuel. Collins et al. demonstrated that infrared irradiation can excite the vibrational-rotational energy bands in solid deuterium, leading to ice redistribution or smoothing, producing an effect similar to the β-homogenization of deuterium-tritium ice. While the generation of smooth hydrogen-deuterium, deuterium-deuterium, and deuterium-tritium ice layers using infrared irradiation has been reported, the target shell absorbs too much infrared light, placing the ice layer in a non-spherical temperature field, resulting in uneven ice thickness. Furthermore, the infrared method requires complex optical systems, which are extremely costly. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for preparing a uniform deuterium layer on the inner surface of a target pellet.

[0004] Technical Solution: The present invention describes a method for preparing a deuterium ice shell layer inside millimeter-scale microspheres. The method is based on a cryogenic target device. The target pellet is suspended in the center of the cryogenic target device sleeve through a deuterium gas filling pipe. By controlling the temperature and pressure, the gaseous deuterium inside the target pellet is first converted into liquid deuterium, and then into polycrystalline solid deuterium. A temperature gradient is then applied to the upper and lower silicon cooling arms to sublimate and condense the polycrystalline solid deuterium in the southern hemisphere of the target pellet into the northern hemisphere to form a relatively uniform deuterium ice layer. The temperature of the upper and lower silicon cooling arms is simultaneously raised to the melting point temperature of the deuterium ice layer, forming a solid-liquid coexisting deuterium layer on the inner surface of the target pellet.

[0005] Specifically, the process of first converting gaseous deuterium inside the target pellet into liquid deuterium, and then into polycrystalline solid deuterium, through temperature and pressure control, involves: controlling the temperature of the cooling rod at 16.5K and the temperature of the upper and lower silicon cooling arms at 18.8K, so that the deuterium gas inside the target pellet liquefies into liquid deuterium; then the heating blocks on the upper and lower silicon cooling arms are turned off, and the liquid deuterium is rapidly frozen to transform into polycrystalline solid deuterium.

[0006] When a temperature gradient is applied to the upper and lower silicon cooling arms, the temperatures of both the upper and lower silicon cooling arms are lower than the melting point of deuterium ice, while the temperature of the lower silicon cooling arm is higher than that of the upper silicon cooling arm.

[0007] The temperature gradient of the upper and lower silicon cooling arms is 0.1K to 1.5K.

[0008] Among them, forming a relatively uniform deuterium ice layer means that the thickness of the deuterium ice layer in the northern and southern hemispheres of the target pellet is equal, at which point the temperature gradient between the upper and lower cooling arms is removed.

[0009] The method for determining that the thickness of the deuterium ice layer in the northern and southern hemispheres is equal is as follows: take pictures of the deuterium ice layer in the northern and southern hemispheres inside the target pellet every 30 to 60 seconds, and obtain the difference in the thickness of the deuterium ice layer in the northern and southern hemispheres by counting the pixels.

[0010] The rate at which the temperature of the upper and lower silicon cooling arms is simultaneously raised to the triple point is 0.1 K / min to 6 K / min.

[0011] Among them, the formation of a solid-liquid coexisting deuterium layer on the inner surface of the target pellet refers to the liquid deuterium encapsulating the deuterium ice within it. Small pieces of polycrystalline deuterium ice easily melt into liquid deuterium, encapsulating the larger pieces of deuterium ice within it.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The method of the present invention can form a smooth, uniform, high-quality solid-liquid coexisting deuterium layer in the target pellet. The average thickness of the obtained deuterium layer is 35.9 μm, the thickness PV value is 4.02 μm, and the inner surface roughness is 1.0 μm, which greatly improves the uniformity and smoothness of the deuterium layer in the target pellet, thus enabling its application in ICF physics experiments. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the cryogenic target device;

[0014] Figure 2 This is a cross-sectional view of the sleeve in the cryogenic target device;

[0015] Figure 3 This diagram illustrates the formation process of the solid-liquid coexisting deuterium layer within the target pellet according to the method of the present invention.

[0016] Figure 4 This is an X-ray phased imaging image. Detailed Implementation

[0017] like Figures 1-4 As shown, the present invention discloses a method for preparing a deuterium ice shell layer inside millimeter-scale microspheres. This method is based on a cryogenic target device, which includes a cooling rod 1, a pressure block 2, upper and lower silicon cooling arms 3, and a sleeve 4. Heating blocks are provided on the upper and lower silicon cooling arms 3. One end of the cooling rod 1 is connected to the secondary cold head of a refrigerator, and the other end of the cooling rod 1 is connected to the upper and lower silicon cooling arms 3 (upper and lower silicon cooling arms) respectively via the pressure block 2. The function of the cooling rod 1 is to transport cold energy from the secondary cold head to the upper and lower silicon cooling arms 3. The function of the pressure block 2 is to connect the cooling rod 1 and the silicon cooling arms 3 with screws. The cooling rod 1 is fixed at one end between the upper and lower silicon cooling arms 3. The outer sides of the two silicon cooling arms 3 are pressure blocks 2. The function of the silicon cooling arms 3 is to transfer the cooling energy from the cooling rod 1 to the sleeve 4. The silicon cooling arms 3 and the sleeve 4 are clamped and fixed. The sleeve 4 contains a target pellet 5. The target pellet 5 is suspended in the center of the sleeve 4 through a deuterium gas filling pipe 6. Another function of the deuterium gas filling pipe 6 is to fill the target pellet 5 with deuterium gas. That is, the target pellet 5 is connected to the deuterium gas filling pipe 6, and the deuterium gas filling pipe 6 delivers deuterium gas to the target pellet 5. The freezing target device fills the sleeve 4 with helium gas through a helium gas filling pipe 7 as a heat transfer medium.

[0018] The temperature of the cooling rod 1 is 16.5K. The temperature of the upper and lower silicon cooling arms 3 is adjusted to 18.8K by the heating blocks on the upper and lower silicon cooling arms 3, causing the pressurized deuterium gas inside the target pellet 5 to liquefy into liquid deuterium. Then, the heating blocks on the upper and lower silicon cooling arms 3 are turned off. At this time, the temperature of the upper and lower silicon cooling arms 3 (between 16.7 and 17K) is slightly higher than the temperature of the cooling rod 1. Rapid freezing causes the liquid deuterium to transform into polycrystalline solid deuterium (due to gravity, only the Southern Hemisphere has a deuterium ice layer at this point). When the deuterium ice begins to melt, this temperature point is determined as the melting point of the deuterium ice (determination of the deuterium ice melting point: after the formation of the deuterium ice layer, the temperature of the upper and lower silicon cooling arms is adjusted; the temperature point corresponding to the observed melting of the deuterium ice layer is the melting point of the deuterium ice). A temperature of 0.5K is applied to the upper and lower silicon cooling arms 3 by the heating blocks on the upper and lower silicon cooling arms 3. A temperature gradient (the temperature in the southern hemisphere of the target pellet is 0.5 K higher than that in the northern hemisphere; due to this temperature difference, deuterium ice migrates from areas of high pressure to areas of low pressure) causes the deuterium ice layer in the southern hemisphere of the target pellet to deposit in the northern hemisphere through a sublimation-deposition process. The thickness of the deuterium ice layer in both hemispheres is controlled by adjusting the duration of the temperature gradient (the duration is 180 s when the average thickness of the deuterium ice layer in the entire target pellet is 35.9 μm). When the thickness of the deuterium ice layer in both hemispheres is equal, the temperature gradient of the upper and lower silicon cooling arms 3 is removed to ensure that the deuterium ice layer in both hemispheres no longer migrates further. Then, the temperature of the upper and lower silicon cooling arms 3 is simultaneously raised to the melting point of deuterium ice at a controlled temperature rate of 3 K / min using a heating block. A uniform, solid-liquid coexisting deuterium layer is formed on the inner surface of the target pellet (this state is maintained for 2–3 min). The method of the present invention can prepare a deuterium layer with uniform thickness and low internal surface roughness inside the target pellet, thereby realizing the preparation of a transient high-quality solid-liquid coexisting deuterium layer inside the target pellet.

[0019] Figure 3 These are X-ray phase images taken during the preparation of a solid-liquid coexisting deuterium layer. Figure 3 A shows the distribution of deuterium ice immediately after flash freezing, where it is concentrated in the southern hemisphere of the target pellet. Then, a temperature gradient is applied to the upper and lower silicon cooling arms, causing the deuterium ice in the southern hemisphere to sublimate and condense onto the northern hemisphere, forming a relatively uniform polycrystalline deuterium ice layer. Figure 3 b). Then, the temperature of the upper and lower silicon cooling arms is raised to the melting point, at which point a uniform, solid-liquid coexisting deuterium layer is formed inside the target pellet. Figure 3 c).

[0020] choose Figure 3 Analysis using c can yield information about the deuterium layer, such as its average thickness, thickness PV value (the difference between the maximum and minimum deuterium layer thickness), and inner surface roughness. First, the outer circle of the target spherical shell is fitted to obtain the pixel values ​​of the precise outer circle center and outer radius. Figure 4 a) Based on the actual parameters of the target, the pixel equivalent is obtained; then the original X-ray phase-contrast image is unfolded in polar coordinates to extract the thickness profile. Figure 4 b) The distribution curve of the deuterium layer thickness with angle is obtained based on the pixel equivalent. Figure 4 c). A Fourier transform was performed on the deuterium layer thickness distribution curve to obtain the modulus-power spectrum curve. Finally, the average thickness of the deuterium layer inside the target pellet was calculated to be 35.9 μm, the thickness PV value was 4.02 μm, and the inner surface roughness was 1.0 μm. This invention achieves complete deuterium ice coverage inside the target pellet by applying a temperature gradient, and then raising the upper and lower silicon cooling arms back to their melting points, forming a smooth, uniform, high-quality solid-liquid coexisting deuterium layer, thereby improving the implosion performance in physical experiments.

Claims

1. A method for preparing a deuterium ice shell layer inside millimeter-scale microspheres, characterized in that, Specifically, the method is based on a cryogenic target device. The target pellet is suspended at the center of the cryogenic target device sleeve through a deuterium gas filling pipe. By controlling the temperature and pressure, the gaseous deuterium inside the target pellet is first converted into liquid deuterium, and then into polycrystalline solid deuterium. A temperature gradient is then applied to the upper and lower silicon cooling arms, causing the polycrystalline solid deuterium in the southern hemisphere of the target pellet to sublimate and condense to form a relatively uniform deuterium ice layer in the northern hemisphere. The temperature of the upper and lower silicon cooling arms is simultaneously raised to the melting point temperature of the deuterium ice layer, forming a solid-liquid coexisting deuterium layer on the inner surface of the target pellet. When the temperature gradient is applied to the upper and lower silicon cooling arms, the temperature of both the upper and lower silicon cooling arms is lower than the melting point temperature of the deuterium ice, and the temperature of the lower silicon cooling arm is higher than that of the upper silicon cooling arm. The temperature gradient between the upper and lower silicon cooling arms is 0.1K to 1.5K.

2. The method for preparing the deuterium ice shell layer inside millimeter-scale microspheres according to claim 1, characterized in that, By controlling temperature and pressure, gaseous deuterium inside the target pellet is first converted into liquid deuterium, and then into polycrystalline solid deuterium. Specifically, the temperature of the cooling rod is controlled at 16.5K and the temperature of the upper and lower silicon cooling arms is controlled at 18.8K, so that the deuterium gas inside the target pellet is liquefied into liquid deuterium; then the heating blocks on the upper and lower silicon cooling arms are turned off, and the liquid deuterium is rapidly frozen to convert into polycrystalline solid deuterium.

3. The method for preparing the deuterium ice shell layer inside millimeter-scale microspheres according to claim 1, characterized in that: The formation of a relatively uniform deuterium ice layer means that the thickness of the deuterium ice layer in the northern and southern hemispheres of the target pellet is equal. At this point, the temperature gradient between the upper and lower cooling arms is removed.

4. The method for preparing the deuterium ice shell layer inside millimeter-scale microspheres according to claim 3, characterized in that: The method for determining whether the thickness of the deuterium ice layer in the Northern and Southern Hemispheres is equal is as follows: take pictures of the deuterium ice layer in the Northern and Southern Hemispheres inside the target pellet at intervals of 30 to 60 seconds, and obtain the difference in the thickness of the deuterium ice layer in the Northern and Southern Hemispheres by counting the pixels.

5. The method for preparing the deuterium ice shell layer inside millimeter-scale microspheres according to claim 1, characterized in that: The rate at which the temperature of the upper and lower silicon cooling arms is simultaneously raised to the triple point is 0.1 K / min to 6 K / min.

6. The method for preparing the deuterium ice shell layer inside millimeter-scale microspheres according to claim 1, characterized in that: The formation of a solid-liquid coexisting deuterium layer on the inner surface of the target pellet refers to the liquid deuterium encapsulating the deuterium ice within it.

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