阅读说明：本技术 利用离子分离抑制黑腔辐射源腔壁等离子体膨胀的方法 (Method for inhibiting plasma expansion of black cavity radiation source cavity wall by ion separation ) 是由 郭亮 李琦 潘凯强 刘耀远 赵航 龚韬 李志超 孙传奎 谢旭飞 杨冬 于 2021-07-20 设计创作，主要内容包括：本发明涉及高能量密度物理技术领域,具体公开了一种利用离子分离抑制黑腔辐射源腔壁等离子体膨胀的方法,包括如下步骤：以高Z元素和低Z元素混合的固体复合材料构造黑腔辐射源的腔壁,腔壁包括激光X光转换层和离子分离层；向黑腔的腔室内部内充入碳氢气体并使气压小于等于0.3倍大气压；采用1ns～30ns脉宽的激光驱动黑腔形成冕区等离子体膨胀受限的辐射源。本发明所公开的方法,在同等充气压力的情况下,复合材料离子分离方法对冕区膨胀的抑制效果更好；减小了激光等离子体相互作用产生的能量亏损、提高激光与黑腔的能量耦合效率更高。(The invention relates to the technical field of high-energy density physics, and particularly discloses a method for inhibiting plasma expansion of a cavity wall of a black cavity radiation source by utilizing ion separation, which comprises the following steps: constructing a cavity wall of a black cavity radiation source by using a solid composite material mixed by high-Z elements and low-Z elements, wherein the cavity wall comprises a laser X-ray conversion layer and an ion separation layer; filling hydrocarbon gas into the cavity of the black cavity and enabling the air pressure to be less than or equal to 0.3 times of atmospheric pressure; the laser with the pulse width of 1-30 ns is adopted to drive the black cavity to form a radiation source with the plasma expansion limitation of the crown area. According to the method disclosed by the invention, under the condition of the same inflation pressure, the composite material ion separation method has a better inhibition effect on the expansion of the corona area; the energy loss generated by the interaction of laser plasma is reduced, and the energy coupling efficiency of laser and a black cavity is improved.)

1. A method for inhibiting plasma expansion of a black cavity radiation source cavity wall by utilizing ion separation is applied to the cavity wall and a cavity of a black cavity radiation source, and is characterized by comprising the following steps:

constructing a cavity wall of a black cavity radiation source by using a solid composite material mixed by high-Z elements and low-Z elements, wherein the cavity wall comprises a laser X-ray conversion layer and an ion separation layer; the thickness of the composite coating subjected to ion separation is more than or equal to 300 nm;

filling hydrocarbon gas into the cavity of the black cavity and enabling the air pressure to be less than or equal to 0.3 times of atmospheric pressure;

the laser with the pulse width of 1-30 ns is adopted to drive the black cavity to form a radiation source with the plasma expansion limitation of the crown area.

2. The method for suppressing plasma expansion in the wall of a black cavity radiation source cavity using ion separation as claimed in claim 1, wherein: the solid composite material comprises pure gold coated with a gold-boron alloy, wherein Au is used as a laser X-ray conversion layer, and AuB is used as an ion separation layer.

3. The method for suppressing plasma expansion of a wall of a radiation source cavity of a black cavity by using ion separation as claimed in claim 1 or 2, wherein: the solid composite material comprises depleted uranium of a uranium nitride coating, wherein DU is a laser X-ray conversion layer, and UN is an ion separation layer.

4. The method for suppressing plasma expansion in the wall of a black cavity radiation source cavity using ion separation as claimed in claim 1, wherein: the nuclear charge number of the atomic nucleus of the high-Z element in the cavity wall solid composite material is more than or equal to 72.

5. The method for suppressing plasma expansion in the wall of a black cavity radiation source cavity using ion separation as claimed in claim 1, wherein: the nuclear charge number of the low-Z element in the cavity wall composite material is less than or equal to 10.

6. The method for suppressing plasma expansion in the wall of a black cavity radiation source cavity using ion separation as claimed in claim 1, wherein: the atomic number of the low-Z element in the cavity wall accounts for more than or equal to 30% of the atomic number of the composite material.

7. The method for suppressing plasma expansion in the wall of a black cavity radiation source cavity using ion separation as claimed in claim 1, wherein: the thickness of the high Z material and the low Z material on the cavity wall is larger than or equal to 300 nm.

8. The method for suppressing plasma expansion in the wall of a black cavity radiation source cavity using ion separation as claimed in claim 1, wherein: the mass ratio of the low-Z component elements of the gas filled into the cavity to the low-Z elements in the cavity wall composite material is 0.8-1.2.

Technical Field

The invention relates to the technical field of high energy density physics, and provides a high-performance black cavity radiation source for various high energy density physical researches such as inertial confinement fusion. Aiming at the problem that the plasma over-expansion of a laser-driven black cavity radiation source cavity wall crown area influences the radiation field intensity and uniformity, the method for inhibiting the plasma expansion of the black cavity radiation source cavity wall by using ion separation is specifically disclosed.

Background

The laser-driven black cavity radiation source can convert nanosecond-scale high-power laser into an extremely strong X-ray radiation field in a cavity made of a high-Z material. The ideal black cavity source requires high conversion efficiency, clean energy spectrum and uniform distribution, but the actual performance and quality of the existing black cavity can not reach the ideal design index, and therefore, various application requirements can not be completely met. One important problem with current black cavity radiation sources is the excessive expansion of the plasma in the wall crown region. The laser irradiates the inner wall of the black cavity, which is quickly ionized into a plasma, the high temperature, low density portion of which is called the corona plasma. Expansion of the crown facing the cavity can sensitively alter the radiation field properties, thereby significantly affecting its effectiveness in various applications. In inertial confinement fusion, plasma in a crown region generated by outer ring laser easily enters an inner ring laser channel when expanding, and the problems of blocked inner ring laser transmission, change of the interaction process of the laser plasma in the inner ring channel, energy transfer change between an inner ring beam and an outer ring beam and the like are caused, so that the energy coupling efficiency of a black cavity is reduced and the irradiation symmetry is deteriorated.

To suppress plasma expansion in the corona region, conventional chamber fillingThe method has three ways of low-Z gas, foaming of cavity wall materials and optimization of black cavity geometric configuration. Intraluminal inflation is the most common and effective means of inhibition. For example, the normal temperature black cavity is filled with neopentane C5H12, and the freezing black cavity is filled with helium He. The gases are rapidly ionized into low-Z plasma in the early stage of laser injection, and the generated thermal pressure can resist the centripetal expansion of the high-Z plasma formed near a focal spot to a certain extent, so that the effective transmission of the inner and outer ring lasers in the pulse width time is ensured. However, large-scale and relatively uniform low-Z gas plasmas are well suited for parametric instability to occur, resulting in back or near-back stimulated brillouin scattering, stimulated raman scattering, etc., resulting in laser energy losses of up to 20% or more. Thus, in some high temperature black cavity designs, inhibition of crown expansion by aeration alone, while maintaining high radiant temperatures, is an unresolved conflict. For this reason, inhibition schemes based on low density foam cell walls have been proposed. The scheme prepares a low-density foamed cavity wall (currently, relatively mature is foamed gold) or a lining low-density foamed Ta on the inner wall of a black cavity₂O₅And the lower sparse wave energy loss after foam ionization is utilized to form the expansion speed lower than that of the solid density material after ionization. However, the wall of the foam cavity is composed of a complex micro-nano structure comprising a skeleton and a gap, and the preparation, regulation and control of the micro structure and the guarantee of the consistency of the micro structure are difficult. Meanwhile, the current radiation fluid program can only process the microstructure simulation through equivalent average density, so that the difference between the simulation design and the experimental result is obvious, and the engineering application of the foam cavity wall is hindered. Recently, in order to inhibit the expansion of the coronal region, research teams at home and abroad develop innovative designs for the cavity wall near the focal spot from the geometric configuration of the black cavity. For example, a hollow wall black cavity designed by French CEA and a peanut type cavity designed by the research institute of applied physics and computational mathematics in Beijing of China all adopt a 'retreat' type design on a gold cavity wall near a focal spot to increase the distance between the cavity wall and a cavity axis, and meanwhile, a layer of ultrathin solid gold is combined at an inward concave part of the original cavity wall to jointly delay the centering time of plasma in a crown region, thereby equivalently realizing the inhibition of expansion of the crown region. The practical effect of the special-shaped black cavity scheme also needs to be confirmed by experiments after the target preparation technology is perfectedWide application is possible.

Therefore, the plasma expansion of the wall of the existing black cavity radiation source cavity cannot be directly and effectively inhibited, and a more reasonable technical scheme needs to be provided to solve the defects in the prior art.

Disclosure of Invention

In order to solve the above mentioned drawbacks of the prior art, the present invention provides a method for suppressing plasma expansion on the wall of a radiation source cavity of a black cavity by using ion separation, which is based on a composite material black cavity filled with gas and utilizes the characteristic of light and heavy ion motion separation in a two-component plasma or even a multi-component plasma formed by composite material ionization to increase the low-Z plasma density in the boundary area between a crown region and a gas region, thereby generating the effect of suppressing the high-Z plasma expansion in the crown region.

In order to achieve the purpose, the invention specifically adopts the technical scheme that:

a method for inhibiting plasma expansion of a black cavity radiation source cavity wall by utilizing ion separation is applied to the cavity wall and a cavity of a black cavity radiation source and comprises the following method steps:

constructing a cavity wall of a black cavity radiation source by using a solid composite material mixed by high-Z elements and low-Z elements, wherein the cavity wall comprises a laser X-ray conversion layer and an ion separation layer; the thickness of the composite coating subjected to ion separation is more than or equal to 300 nm;

filling hydrocarbon gas into the cavity of the black cavity and enabling the air pressure to be less than or equal to 0.3 times of atmospheric pressure;

the laser with the pulse width of 1-30 ns is adopted to drive the black cavity to form a radiation source with the plasma expansion limitation of the crown area.

The method for suppressing expansion disclosed above uses ion separation to manipulate the plasma density spatial-temporal distribution in and around the black-cavity crown region. Ion separation refers to the phenomenon that in a two-component or even multi-component plasma, different kinds of ions are separated macroscopically in space due to the difference of self-mass, charge and mean free path and the fluid movement of the ions under the influence of certain external factors such as pressure gradient, temperature gradient and self-generated electromagnetic field.

According to the invention, a composite material is formed by adopting high-Z elements and low-Z elements in an atom mixing mode and is used in an area directly ablated by laser in a black cavity wall, and meanwhile, the black cavity is filled with low-Z gas with certain pressure; the inner wall of the black cavity is directly ablated by laser to form high-low Z mixed corona area plasma, and due to the mass difference of high-low Z ions, the low-Z light ions on the cavity wall are faster than the high-Z heavy ions on the cavity wall when moving towards the cavity axis; the nuclear mass ratio of the cavity wall low-Z ions is close to that of the gas area low-Z ions, so that the separated cavity wall low-Z ions are easily mixed with the gas low-Z ions at the junction of the crown area and the gas area, the density of the low-Z ions in the mixed area is greatly increased, which is equivalent to improving the initial inflation pressure of the local area, and the effect of inhibiting the plasma expansion of the cavity wall high-Z ions and the crown area is generated.

Further, in the present invention, the solid composite material can be made of various materials, and is optimized and one of the following possible choices is provided: the solid composite material comprises pure gold coated with a gold-boron alloy, wherein Au is used as a laser X-ray conversion layer, and AuB is used as an ion separation layer.

Still further, optimization is performed here to give another possible solid composite: the solid composite material comprises depleted uranium of a uranium nitride coating, wherein DU is a laser X-ray conversion layer, and UN is an ion separation layer.

Further, in the present invention, the material of the cavity wall of the black cavity needs to be optimized, and the solid composite material for the cavity wall is optimized here, which is one of the following feasible options: the nuclear charge number of the atomic nucleus of the high-Z element in the cavity wall solid composite material is more than or equal to 72.

Further, the present invention optimizes the solid composite material for the chamber wall, including one of the following possible options: the nuclear charge number of the low-Z element in the cavity wall composite material is less than or equal to 10.

Further, the present invention optimizes the composition ratio of the solid composite material used in the cavity wall, which is one of the following possible options: the atomic number of the low-Z element in the cavity wall accounts for more than or equal to 30% of the atomic number of the composite material.

Further, the present invention optimizes the thickness of the solid composite material on the chamber wall, which is one possible option: the thickness of the high Z material and the low Z material on the cavity wall is larger than or equal to 300 nm.

Still further, the invention optimizes the gas composition in the black cavity, which is a feasible choice: the mass ratio of the low-Z component elements of the gas filled into the cavity to the low-Z elements in the cavity wall composite material is 0.8-1.2.

Compared with the prior art, the invention has the beneficial effects that:

1. under the condition of the same inflation pressure, the composite material ion separation method has better inhibiting effect on the expansion of the corona area.

2. To achieve the same level of suppression, the composite ion separation method allows for lower gas charging pressures, which is better for reducing the energy loss due to laser-plasma interaction and improving the energy coupling efficiency of the laser and black cavity.

3. The existing technology for preparing the atomic-level mixed composite material based on magnetron sputtering is mature, and compared with the preparation difficulty of a foaming cavity wall and a black cavity with a specially-shaped focal spot area, the technical scheme disclosed by the invention has a better application prospect.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a schematic diagram of laser ablation of a chamber wall to form a plasma in the corona region and thereby achieve motion separation.

Figure 2 is a schematic illustration of ion separation of composite material crown regions to inhibit crown region expansion.

FIG. 3 is a flow chart of the suppressing method disclosed in the present invention.

Fig. 4 shows the contrast effect of the X-ray observation image of pure Au cavity crown area movement and the X-ray observation image of DU + UN cavity crown area movement.

FIG. 5 is a schematic diagram showing the comparison of the two rings of focal spot distributions of the pure Au cavity crown area moving X-ray observation image and the DU + UN cavity crown area moving X-ray observation image.

Detailed Description

The invention is further explained below with reference to the drawings and the specific embodiments.

It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. Specific structural and functional details disclosed herein are merely illustrative of example embodiments of the invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.

Example 1

The embodiment provides a suppression method for effectively suppressing plasma expansion in the case of plasma expansion in the conventional black cavity radiation source.

As shown in fig. 4 and 5, in the ICF-related physical experiment, injection port images of black cavity sources of different cavity wall materials were measured by an X-ray vacuum camera. Under the condition that the peak radiation temperature formed by the action of 3ns square wave laser is 210eV, the expansion scale of the crown area of the DU + UN black cavity is estimated to be reduced by 55 percent compared with that of a pure Au cavity.

Specifically, as shown in fig. 3, the technical solution disclosed in this embodiment is as follows:

a method for inhibiting plasma expansion of a black cavity radiation source cavity wall by utilizing ion separation is applied to the cavity wall and a cavity of a black cavity radiation source and comprises the following method steps:

s01: constructing a cavity wall of a black cavity radiation source by using a solid composite material mixed by high-Z elements and low-Z elements, wherein the cavity wall comprises a laser X-ray conversion layer and an ion separation layer; the thickness of the composite coating subjected to ion separation is more than or equal to 300 nm;

s02: filling hydrocarbon gas into the cavity of the black cavity and enabling the air pressure to be less than or equal to 0.3 times of atmospheric pressure;

preferably, the hydrocarbon gas in this embodiment may be neopentane.

S03: the laser with the pulse width of 1-30 ns is adopted to drive the black cavity to form a radiation source with the plasma expansion limitation of the crown area.

The method for suppressing expansion disclosed above uses ion separation to manipulate the plasma density spatial-temporal distribution in and around the black-cavity crown region. Ion separation refers to the phenomenon that in a two-component or even multi-component plasma, different kinds of ions are separated macroscopically in space due to the difference of self-mass, charge and mean free path and the fluid movement of the ions under the influence of certain external factors such as pressure gradient, temperature gradient and self-generated electromagnetic field.

In the embodiment, a composite material is formed by adopting high-Z elements and low-Z elements in an atom mixing mode and is used in an area directly ablated by laser in a black cavity wall, and meanwhile, the black cavity is filled with low-Z gas with certain pressure; the inner wall of the black cavity is directly ablated by laser to form high-low Z mixed corona area plasma, and due to the mass difference of high-low Z ions, the low-Z light ions on the cavity wall are faster than the high-Z heavy ions on the cavity wall when moving towards the cavity axis; the nuclear mass ratio of the cavity wall low-Z ions is close to that of the gas area low-Z ions, so that the separated cavity wall low-Z ions are easily mixed with the gas low-Z ions at the junction of the crown area and the gas area, the density of the low-Z ions in the mixed area is greatly increased, which is equivalent to improving the initial inflation pressure of the local area, and the effect of inhibiting the plasma expansion of the cavity wall high-Z ions and the crown area is generated.

Preferably, in this embodiment, the solid composite material may be made of a plurality of materials, and is optimized and one of the following possible choices is provided: the solid composite material comprises pure gold coated with a gold-boron alloy, wherein Au is used as a laser X-ray conversion layer, and AuB is used as an ion separation layer. AuB is a composite material layer developed for reducing the loss of scattered light of a black cavity radiation source in the past, has the capability of precisely controlling the thickness and the atomic ratio at home and abroad after the preparation technology is accumulated for many years, and has more feasibility and practicability compared with other high-low Z material combinations AuB which are not verified by experiments.

In this embodiment, the wall material of the black cavity needs to be optimized, and the solid composite material for the wall is optimized here, which is one of the following possible options: the nuclear charge number of the atomic nucleus of the high-Z element in the cavity wall solid composite material is more than or equal to 72. The main reasons are as follows: the purpose of the black cavity radiation source is to generate high temperature, high flux X-rays, and studies have shown that materials with higher atomic numbers have higher laser X-ray conversion efficiencies. Considering both cost and stability, the selection of materials therefore focuses on the sixth and above period of the periodic table. Au and U are most commonly used, the Au conversion efficiency is high, and the preparation is relatively easy; u is the highest atomic number material available at present, the conversion efficiency is better, and although the oxidation is easy, the oxidation resistance technology is mature at present.

Preferably, the number of nuclear charges of the nucleus of the high Z element used in this embodiment is 72, and a single high Z element is used in this embodiment.

In other embodiments, a plurality of high-Z elements may be combined, for example, a plurality of materials formed by a plurality of elements with nuclear charge numbers of 75, 80, 82, and 85 are used, and the combination ratio between different materials is adjusted according to actual requirements.

This example optimizes the solid composite material for the chamber walls, giving one possible option: the nuclear charge number of the low-Z element in the cavity wall composite material is less than or equal to 10. Referring to the experiment of purely researching the separation phenomenon of CH material ions abroad, the mass ratio of two elements C and H of the composite material with obvious separation characteristics which is proved at present is 12, and if the mass ratio of high-Z elements to low-Z elements in the composite material is not lower than 12, the low-Z atomic number is required to be not higher than 10.

Preferably, a material formed of a low Z element having a nuclear charge number of 5 may be used in the present embodiment, and a single material is used in the embodiment.

In other embodiments, a plurality of low Z elements may be used in combination, for example, different materials formed by low Z elements with nuclear charge numbers of 2, 4, 6, and 8 may be used, and the proportioning combination of the materials is set according to actual requirements.

This example optimizes the composition ratio of the solid composite material used in the chamber wall, using one of the following possible options: the atomic number of the low-Z element in the cavity wall accounts for more than or equal to 30% of the atomic number of the composite material. The concentration of low-Z ions is guaranteed to ensure that the ion density of a gas junction area can be effectively improved after the low-Z ions are separated, the N percentage of UN which is applied currently is not less than 50%, and the B percentage of AuB is not less than 30%.

This embodiment optimizes the thickness of the solid composite material on the chamber walls, where one of the following possible options is used: the thickness of the high Z material and the low Z material on the cavity wall is larger than or equal to 300 nm. The comparison experiment shows that when the thickness of the composite material is 100nm, the expansion speed of the composite material is basically consistent with that of the cavity wall without the composite material; the expansion rate was reduced by about 50% when the composite thickness was 600nm compared to the wall without the composite wall. Thus taking half the thickness of 600nm as an effective criterion. The expansion is reduced by about 55% as shown in fig. 4, 5 using depleted uranium which is most effectively 700nmUN coating.

As shown in fig. 4 and 5, in the ICF-related physical experiment, injection port images of black cavity sources of different cavity wall materials were measured by an X-ray vacuum camera. Under the condition that the peak radiation temperature formed by the action of 3ns square wave laser is 210eV, the expansion scale of the crown area of the DU + UN black cavity is estimated to be reduced by 55 percent compared with that of a pure Au cavity.

This example optimizes the composition of the gas in the black chamber using one of the following possible options: the mass ratio of the low-Z component elements of the gas filled into the cavity to the low-Z elements in the cavity wall composite material is 0.8-1.2. The main purpose of the method is to enable the mass of main ions in a gas area to be close to that of low-Z ions separated from a composite wall material, so that the fluid behaviors of the two low-Z ions in a contact area are close to each other, and density stacking is formed more quickly to block expansion of the high-Z ions.

Preferably, the mass ratio of the low-Z component element of the gas to the low-Z element in the chamber wall conforming material is set to 1. In other embodiments, the mass ratio may also be set to 0.8, 0.9, 1.1, or 1.2.

In the radiation process of the black cavity radiation source, the motion process of the plasma is as follows:

as shown in fig. 1, when the laser directly ablates the black cavity of the uranium nitride coating, the solid uranium nitride material is ionized into high-temperature corona plasma in the focal spot region, and the components of the high-temperature corona plasma include U ions and N ions; while the gas zone (neopentane) is ionized mainly by the converted X-rays into a relatively low temperature gas plasma represented by C ions; the high temperature corona plasma generally moves in a sparse manner toward the corona low temperature gas region, and the movement of light (N) heavy (U) ions is separated in the early stage of the movement, i.e., the N ions move faster than the U ions.

The scheme of the embodiment is used for inhibiting plasma volume expansion, and the specific process is as follows:

as shown in fig. 2, the movement of the crown area may compress ions in the gas area C, and the compression process causes the ion density in the boundary area C to increase, thereby generating a reverse pressure resisting the movement of the crown area, wherein the higher the ion density of C, the higher the reverse pressure is, the better the resisting effect is; at the same gas pressure, U, N ions formed by uranium nitride rapidly and remarkably increase the density of low-Z ions (including C, N) in the boundary area due to motion separation, and the reverse pressure is increased so as to inhibit the motion of U ions.

Example 2

The embodiment discloses a method for inhibiting plasma expansion of a wall of a radiation source cavity of a black cavity by using ion separation, which is different from the method in embodiment 1 in that the embodiment improves a solid composite material applied to the black cavity, and specifically comprises the following steps:

the present embodiment is optimized to use a feasible solid composite material: the solid composite material comprises depleted uranium of a uranium nitride coating, wherein DU is a laser X-ray conversion layer, and UN is an ion separation layer.

The UN is a composite material layer developed for resisting pure U material evolution in the past, has precise control capability for thickness and atomic ratio in China after years of preparation technology accumulation, and is more feasible and practical compared with other high-low Z material combination UN which is not verified by experiments.

Other steps and features not described in this embodiment are the same as those in embodiment 1, and are not described again here.

The above embodiments are just exemplified in the present embodiment, but the present embodiment is not limited to the above alternative embodiments, and those skilled in the art can obtain other various embodiments by arbitrarily combining with each other according to the above embodiments, and any other various embodiments can be obtained by anyone in light of the present embodiment. The above detailed description should not be construed as limiting the scope of the present embodiments, which should be defined in the claims, and the description should be used for interpreting the claims.