High-temperature high-density plasma generation and radiation opacity measurement method

Abstract

The invention discloses a high-temperature high-density plasma generation and radiation opacity measurement method, which comprises the following steps: clamping a target material by using low-density low-Z-element foam to form a sandwich structure sample, and synchronously and directly driving the sandwich sample from two sides by using multiple beams of smooth nanosecond laser, the preparation temperature reaches 1,000,000 DEG C, and the electron density reaches 1 * 1023 pieces per cubic centimeter; then generating an X-ray source through the action of one or more nanosecond laser beams and the high-Z material, measuring the absorption spectrum of the X-ray source penetrating through the target plasma, the backlight spectrum of the X-ray source not penetrating through the target plasma and the self-emission spectrum of the target plasma through a spectrograph, and finally realizing the measurement of the radiation opacity of the high-temperature and high-density plasma. The high-temperature and high-density plasma radiation opaqueness measurement device has the beneficial effects that the high-temperature and high-density plasma radiation opaqueness measurement of which the temperature reaches 1,000,000 DEG C and the electron density reaches 1 * 1023 per cubic centimeter is realized on a million-joule nanosecond laser device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-energy-density physics, and in particular to a method for generating high-temperature and high-density plasma and measuring radiation opacity. BACKGROUND

[0002] High-temperature and high-density plasmas exist widely in controlled nuclear fusion and astrophysics and other high-energy-density physics systems. The radiation opacity of the high-temperature and high-density plasma is a key basic parameter that affects the radiation energy transport in the plasma system and is of great research value. However, the accurate calculation of the radiation opacity of the high-temperature and high-density plasma with complex physical characteristics such as multi-body strong coupling, strong nonlinearity and multi-time-space scale still faces great challenges. Therefore, countries around the world have carried out experimental research on the radiation opacity of plasma under extreme temperature and density conditions by means of large scientific devices such as large lasers, Z pinches and free electron lasers. Experimental data have played an extremely important role in verifying and promoting the progress of physical models and have promoted the improvement of the engineering design capability of inertial confinement fusion and the progress of stellar physics observation technology.

[0003] Since the 1990s, the United States has proposed and implemented a high-temperature and high-density plasma generation technology based on indirect driving of a sandwich sample by a black cavity X-ray radiation field on the Nova nanosecond laser device, and has established a traditional experimental method for radiation opacity. Up to now, the National Ignition Facility (NIF) device (total laser energy 1.4 million joules) of the United States and the Shenguang series devices (total laser energy 0.2-10 million joules) of China also use this technology to heat the temperature of the sample to 100 million degrees and the electron density to the order of 10 21 to 10 22 million per cubic centimeter. At present, the United States has obtained a high-temperature and high-density plasma with an electron density of up to 2×10 22 million per cubic centimeter by using the world's largest nanosecond laser device (NIF device), and has found that the radiation opacity increases more and more significantly with the increase of the electron density, which has aroused people's thinking about whether the existing calculation program of the radiation opacity of high-temperature and high-density plasma is complete. Therefore, it is of great significance to carry out experimental research on the radiation opacity of plasma with a temperature of 100 million degrees and a higher electron density (more than 2×10 22 million per cubic centimeter) based on a nanosecond laser device with a power of 10 million joules. The related research is a continuous research hotspot in the field of international high-energy-density physics and extreme conditions atomic molecules.

[0004] However, based on the widely used traditional radiation heating plasma generation method, the electron density of the plasma is continuously increased from 2×10 22 million per cubic centimeter to 1×10 23There are two technical defects that cannot be solved:

[0005] First, the energy utilization efficiency is low. In the traditional indirect driving method, X-ray radiation field is generated by the interaction of multiple high-energy lasers and high-Z material-made black cavity, and then the sample is indirectly irradiated by the X-ray radiation field to achieve heating, so that the sample reaches a high-temperature and high-density plasma state. This process has two energy conversion processes. The energy conversion efficiency from laser to X-ray radiation field driving the sample is generally only about 10%, and the laser energy utilization rate is extremely low.

[0006] Second, it is difficult to create and maintain a high-density plasma state with an electron density of 1×10 23 per cubic centimeter under the premise of ensuring a temperature of 100 million degrees. Due to the limitation of energy conversion efficiency, in order to allow the sample to more fully absorb the energy of the X-ray radiation to achieve a high enough temperature state, a thin sandwich sample is usually used. However, under the premise of maintaining a temperature of 100 million degrees, the electron density can only reach 10 22 per cubic centimeter, and it is difficult to further improve. For example, if the electron density is increased to 1×10 23 per cubic centimeter, the pressure of the sample plasma will increase several times, which will cause the sample plasma to rapidly expand and become sparse, so it is difficult to create a high-temperature and high-density plasma state with an electron density of 1×10 23 per cubic centimeter or more and maintain it for a sufficient time.

[0007] In summary, the traditional indirect driving method cannot be applied to high-temperature and high-density plasma radiation opacity experiments with a temperature of 100 million degrees and an electron density of 1×10 23 per cubic centimeter. The technical difficulties mainly include: on the one hand, it is necessary to ensure the energy conversion efficiency as much as possible to improve economic efficiency; on the other hand, it is necessary to create more extreme plasma temperature and density states and maintain them for a sufficient time to effectively maintain the plasma state within the diagnostic measurement time window.

[0008] Therefore, it is necessary to establish a new radiation opacity experimental research method to overcome the technical defects of the traditional method, such as low energy conversion efficiency and difficulty in creating a high-density high-temperature plasma state, and to fill the gap in related technologies. SUMMARY

[0009] Therefore, the present application provides a high-temperature and high-density plasma generation and radiation opacity measurement method, which realizes high-temperature and high-density plasma radiation opacity measurement with a temperature of 100 million degrees and an electron density of 1×10 23 per cubic centimeter on a nanosecond laser device with a power of 100 joules.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A method for generating high-temperature, high-density plasma and measuring radiation opacity, the key of which includes the following steps:

[0012] Step S1, prepare a multi-layer sample target: prepare a sample to be irradiated and two low-Z foams, and clamp the sample between the two low-Z foams.

[0013] Step S2, generating high-temperature, high-density plasma: Laser beams are respectively mounted on both sides of the multilayer sample target, and the laser beams on both sides act synchronously on the central region of the multilayer sample target. The laser beams first heat the low-Z foam and generate thermionic electrons, and then use the thermionic electrons to heat the sample in the middle, so that the sample reaches a temperature of 1 million degrees and an electron density of 1×10⁻⁶. 23 One-dimensional flat plate high-temperature high-density plasma per cubic centimeter;

[0014] Step S3, radiation opacity measurement;

[0015] Step S3.1: An X-ray backlight source is set on one side of the sample, and an X-ray spectrometer is set on the other side. The X-ray spectrometer includes a spectrometer element and a recording surface. The spectrometer element is used to separate X-rays into X-ray spectra at different energy points, and the recording surface is used to record the X-ray spectra.

[0016] Step S3.2: Perform time-resolved and spatially resolved X-ray spectral measurements using the X-ray spectrometer. The X-ray backlight emits X-rays, ensuring that part of the rays passes through the sample and strikes the spectrometer, while part strikes the spectrometer directly. Then, record three types of spectra through three regions on the recording surface: the absorption intensity I of the X-ray backlight source passing through the sample. A Backlight spectral intensity I that does not penetrate the sample B and the sample's self-emission intensity I E ;

[0017] Step S3.3: Calculate the radiation opacity. Based on the transmittance spectrum calculation formula, obtain the transmittance spectrum T of the high-temperature, high-density plasma. Then, combine it with the initial density ρ and thickness l of the sample to obtain the radiation opacity μ. The calculation formulas for transmittance spectrum T and radiation opacity μ are as follows:

[0018]

[0019] Preferably, in step S2, the laser beam on each side of the multilayer sample target consists of multiple kilojoule nanosecond lasers, and the nanosecond lasers need to be beam-smoothed on the target surface to obtain a power density of ~10. 13A uniform laser field with a power of watts per square centimeter, a duration of 1-2 nanoseconds, and a spot diameter of not less than 800 micrometers.

[0020] Preferably, in step S1, the low-Z foam has a thickness of 50-150 micrometers and a density of 50-150 milligrams per cubic centimeter, and the sample thickness is 0.1-0.3 micrometers.

[0021] Preferably, in step S1, the low-Z foam has a cylindrical structure, the sample has a semi-circular plate structure, and the diameter of the low-Z foam and the sample is greater than the diameter of the nanosecond laser spot.

[0022] Preferably, the low-Z foam block is a hydrocarbon or boron foam.

[0023] Preferably, in step S3, the X-ray backlight source is generated by the interaction of one or more laser beams with a high-Z material, wherein the laser power density is greater than 1×10⁻⁶. 14 W / cm 2 .

[0024] Preferably, the beam splitter is a crystal or a grating.

[0025] Preferably, in step S3, the time resolution is controlled by a pulsed laser driving the backlight material, and the pulse width of the pulsed laser is less than 200 ps; or the time resolution is achieved by recording with a time resolution device.

[0026] Preferably, in step S3, spatial resolution is achieved using a point backlight or a spatial resolution slit, wherein the width of the spatial resolution slit is 50-200 micrometers.

[0027] Preferably, in step S2, the synchronization deviation of the laser beams on both sides of the multilayer sample target needs to be controlled within ±100 picoseconds, and the total energy deviation needs to be controlled within 10%; the center of the focal spot of the multi-path laser superposition on each side needs to be controlled within ±100 micrometers.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] Using the high-temperature, high-density plasma generation and radiation opacity measurement method provided by this invention, temperatures reaching 1 million degrees Celsius and electron densities reaching 1 × 10⁻⁶ can be achieved on a 10,000 joule-level device. 23 The measurement of high-temperature, high-density plasma radiation opacity per cubic centimeter solves the technical defects of traditional radiation heating technology, such as low energy utilization and difficulty in maintaining a high-density plasma state. Attached Figure Description

[0030] Figure 1-1 A schematic diagram illustrating the direct generation of high-temperature, high-density sample plasma;

[0031] Figure 1-2 This is a schematic diagram of the radiation opacity experiment measurement;

[0032] Figure 2 The time evolution of temperature Te and electron density Ne in a high-temperature, high-density Si plasma is shown (red line represents temperature, blue line represents electron density). Within the time range of 0.75–1.05 nanoseconds, the plasma temperature is approximately 110 electron volts (approximately 1.2 million degrees Celsius), and the electron density is approximately 1.4 × 10⁻⁶. 23 For each cubic centimeter, the backlight with a resolution of 0.2 nanoseconds was measured within the range of 0.8-1.0 nanoseconds.

[0033] Figure 3 The X-ray energy spectra for three regions with an energy range of 1770-1850 eV obtained in the experiment are shown. The black area represents the absorption intensity I of the X-ray backlight source passing through the sample. A (Including sample self-emission intensity I) E (Red represents the backlight intensity I that did not penetrate the sample) B (Including sample self-emission intensity I) E (The blue color represents the individual sample's self-emission intensity I.) E ;

[0034] Figure 4 The transmittance spectrum of high-temperature, high-density plasma is obtained according to formula (1). Detailed Implementation

[0035] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0036] This embodiment provides a method for generating high-temperature, high-density plasma and measuring radiation opacity, implemented on a megajoule-level nanosecond laser device. The specific steps are as follows (please refer to the documentation). Figure 1-1 and Figure 1-2 As shown:

[0037] Step S1, Preparation of a multi-layer sample target: Prepare a sample 2 to be irradiated and two low-Z foams 4. The sample 2 is sandwiched between the two low-Z foams 4, wherein the low-Z foam 4 has a cylindrical structure and the sample 2 has a semi-circular plate structure. In this embodiment, the low-Z foam is hydrocarbon (CH) or boron (B) foam, the thickness of the low-Z foam 4 is 50-150 micrometers, and the density is 50-150 milligrams per cubic centimeter. To ensure that the laser is used entirely for heating the sample, the diameter of the low-Z foam and the sample must be greater than the diameter of the laser spot, or the area of ​​the low-Z foam and the sample must be greater than the area of ​​the laser spot. In this embodiment, the diameter of the foam and the sample is greater than 800 micrometers. To obtain a clear experimental absorption spectrum at 1 million degrees Celsius and to ensure the uniformity of the sample's spatial state, the sample thickness is required to be 0.1-0.3 micrometers.

[0038] The reasons for setting the thickness of the low-Z foam 4 to 50-150 micrometers are as follows: If the low-Z foam is too thin, it cannot effectively compress the sample, resulting in the sample not reaching and maintaining a high density. Secondly, the laser will burn the low-Z foam, preventing thermionic heating of the sample at the center. If the low-Z foam is too thick, it will result in insufficient sample heating, and the sample temperature will not reach 1 million degrees Celsius.

[0039] Step S2, generating high-temperature, high-density plasma: Laser beams 3 are respectively mounted on both sides of the multi-layer sample target, and the laser beams 3 on both sides act synchronously on the central region of the multi-layer sample target. The laser beams 3 first heat the low-Z foam 4 and generate thermionic electrons, and then use the thermionic electrons to heat the sample 2 in the middle, so that the sample 2 reaches a temperature of 1 million degrees and an electron density of 1×10⁻⁶. 23 One-dimensional flat plate high-temperature high-density plasma per cubic centimeter.

[0040] In this step, the laser beam 3 on each side of the multilayer sample target consists of multiple kilojoule nanosecond lasers. The nanosecond lasers need to be beam-smoothed on the target surface to obtain a power density of ~10. 13 A uniform laser field with a power density on the order of watts per square centimeter, a duration of 1-2 nanoseconds, and a spot diameter of not less than 800 micrometers. To create a temperature state of 1 million degrees Celsius, the laser power density obtained on the surface of a multi-layer sample target needs to be higher than 1 × 10⁻⁶. 13 Watts per square centimeter. To meet the measurement requirements of 100-200 picoseconds for diagnostic time resolution, the sample state duration must be greater than 300 picoseconds, the sample cannot be heated or cooled too quickly, and the laser power density must be controlled below 1×10⁻⁶. 14 Tiles per square centimeter.

[0041] In this step, the synchronization deviation of the laser beams 3 on the upper and lower sides of the multilayer sample target needs to be controlled within ±100 picoseconds, the total energy deviation needs to be controlled within 10%, and the center of the focal spot of the multi-laser superposition on each side needs to be controlled within ±100 micrometers to ensure the temporal and spatial uniformity of the laser in the loading area.

[0042] The role of low-Z foam is to generate a thermionic heating source and suppress the expansion of the heated sample to maintain its already achieved high density state, while ensuring that the laser does not directly act on the encapsulated sample within the laser pulse timescale. A laser pulse width of 1 nanosecond and a laser power density of 3 × 10⁻⁶ are used. 13 Taking a low-Z foam density of 100 milligrams per cubic centimeter and a thickness of 100 micrometers as an example, with a density of 100 milligrams per cubic centimeter and a thickness of 100 micrometers, it is possible to create temperatures exceeding 1 million degrees Celsius and electron densities reaching 1×10⁻⁶. 23 A high-temperature, high-density plasma state with a density of more than one cubic centimeter is controlled to exist on a timescale greater than 300 picoseconds.

[0043] Step S3, radiation opacity measurement.

[0044] Step S3.1: An X-ray backlight source 6 is set on one side of sample 2, and an X-ray spectrometer 5 is set on the other side. The X-ray backlight source 6 is generated by one or more laser beams interacting with the high-Z material, and its laser power density is greater than 1×10⁻⁶. 14 W / cm 2 The X-ray spectrometer 5 includes a beam splitter 51 and a recording surface 52. In this embodiment, the beam splitter 51 is a crystal or a grating, and the recording surface 52 is an X-ray film, an imaging plate, or an X-ray framing camera. The beam splitter 51 is used to separate X-rays into X-ray spectra at different energy points, and the recording surface 52 is used to record the X-ray spectra.

[0045] Step S3.2: Time-resolved and spatial-resolved X-ray spectroscopy measurements are performed using the X-ray spectrometer 5. Specifically, the X-ray backlight source 6 emits X-rays, ensuring that part of the rays passes through the sample 2 and strikes the spectrometer 51, while part strikes the spectrometer 51 directly. Then, three types of spectra are recorded through three regions on the recording surface 52: the absorption intensity I of the X-ray backlight source 6 passing through the sample 2. A (Including sample self-emission intensity I) E ), backlight spectral intensity I that did not pass through sample 2 B (Including sample self-emission intensity I) E ), and the self-emission intensity I of sample 2 E .

[0046] In this step, temporal resolution is controlled by a pulsed laser driving the backlight material, with a pulse width of less than 200 ps; or temporal resolution is achieved by recording with a temporal resolution device, such as an X-ray framing camera, where the temporal resolution is less than 200 ps. Spatial resolution is controlled by a point backlight or a spatial resolution slit.

[0047] In this step, since the duration of the high-temperature, high-density plasma is greater than 300 picoseconds, a diagnostic time resolution of less than 200 picoseconds is sufficient to meet the requirements for time-uniform plasma measurements. The spatial area of ​​the high-temperature, high-density plasma is comparable to the laser spot size, approximately 800-1000 micrometers, the size of the X-ray backlight 6 is approximately 200 micrometers, and the width of the spatial resolution slit is approximately 50-200 micrometers. Therefore, this spatial resolution level meets the requirements for measurements in three spectral regions.

[0048] Step S3.3: Calculate the radiation opacity. Based on the transmittance spectrum calculation formula, obtain the transmittance spectrum T of the high-temperature, high-density plasma. Then, combine it with the initial density ρ and thickness l of the sample to obtain the radiation opacity μ. The calculation formulas for transmittance spectrum T and radiation opacity μ are as follows:

[0049]

[0050] In the experimental method, only the transmittance spectrum T needs to be obtained.

[0051] To verify the feasibility of the above method, a temperature of 100 eV and an electron density greater than 1 × 10⁻⁶ were achieved on my country's Shenguang III prototype nanosecond laser device, which operates at a rate of 10,000 joules. 23 cm -3 Taking the generation of one-dimensional flat plate high-temperature high-density plasma and the measurement of radiation opacity as an example, a detailed explanation is given.

[0052] refer to Figures 2 to 4 The experimental laser conditions were as follows: Two laser beams were selected for the upper beam group, each with an energy of 800 joules, a pulse width of 1 nanosecond, and a spot diameter of 800 micrometers; two laser beams were selected for the lower beam group, with the same parameters and synchronized timing as the upper beam group. Target conditions were as follows: CH foam had a thickness of 90 micrometers, a density of 100 milligrams per cubic centimeter, and a diameter of 1300 micrometers; the encapsulated circular semi-sample Si had a density of 2.3 g per cubic centimeter, a thickness of 0.3 micrometers, and a diameter consistent with the foam. A high-Z element Dy backlight was used, with the backlight-driven laser having an energy of 200 joules, a pulse width of 0.2 nanoseconds, and a focused spot diameter of 200 micrometers. The backlight-driven laser was delayed by 0.8 nanoseconds relative to the heating laser. A planar crystal spectrometer was used for X-ray spectroscopy to measure the Si plasma in the 0.8-1.0 nanosecond time range, with a temperature of approximately 110 eV (approximately 1.2 million degrees Celsius) and an electron density of approximately 1.4 × 10⁻⁶. 23 The X-ray energy spectrum is obtained in three spatial regions with an energy range of 1770-1850 electron volts per cubic centimeter. Finally, the transmittance spectrum can be obtained.

[0053] This embodiment verifies the feasibility of the method of the present invention. By controlling the laser parameters, sample structure, and measurement conditions, a temperature of 1 million degrees Celsius and an electron density of 1 × 10⁻⁶ were successfully achieved on a megajoule-level device. 23 The measurement of high-temperature, high-density plasma radiation opacity per cubic centimeter solves the technical defects of traditional radiation heating technology, such as low energy utilization and difficulty in maintaining a high-density plasma state.

[0054] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. A method for generating high-temperature, high-density plasma and measuring radiation opacity, characterized in that, Includes the following steps: Step S1, prepare a multi-layer sample target: prepare a sample to be irradiated and two low-Z foams, and clamp the sample between the two low-Z foams. Step S2, generating high-temperature, high-density plasma: Laser beams are respectively mounted on both sides of the multilayer sample target, and the laser beams on both sides act synchronously on the central region of the multilayer sample target. The laser beams first heat the low-Z foam and generate thermionic electrons, and then use the thermionic electrons to heat the sample in the middle, so that the sample reaches a temperature of 1 million degrees and an electron density of 1×10⁻⁶. 23 One-dimensional flat plate high-temperature high-density plasma per cubic centimeter; Step S3, radiation opacity measurement; Step S3.1: An X-ray backlight source is set on one side of the sample, and an X-ray spectrometer is set on the other side. The X-ray spectrometer includes a spectrometer element and a recording surface. The spectrometer element is used to separate X-rays into X-ray spectra at different energy points, and the recording surface is used to record the X-ray spectra. Step S3.2: Perform time-resolved and spatially resolved X-ray spectral measurements using the X-ray spectrometer. The X-ray backlight emits X-rays, ensuring that part of the rays passes through the sample and strikes the spectrometer, while part strikes the spectrometer directly. Then, record three types of spectra through three regions on the recording surface: the absorption intensity I of the X-ray backlight source passing through the sample. A Backlight spectral intensity I that does not penetrate the sample B and the sample's self-emission intensity I E ; Step S3.3: Calculate the radiation opacity. Based on the transmittance spectrum calculation formula, obtain the transmittance spectrum T of the high-temperature, high-density plasma. Then, combine it with the initial density ρ and thickness l of the sample to obtain the radiation opacity μ. The calculation formulas for transmittance spectrum T and radiation opacity μ are as follows:

2. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: In step S2, the laser beam on each side of the multilayer sample target consists of multiple kilojoule nanosecond lasers. The nanosecond lasers need to be beam-smoothed on the target surface to obtain a power density of ~10. 13 A uniform laser field with a power of watts per square centimeter, a duration of 1-2 nanoseconds, and a spot diameter of not less than 800 micrometers.

3. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: In step S1, the low-Z foam has a thickness of 50-150 micrometers and a density of 50-150 milligrams per cubic centimeter, and the sample thickness is 0.1-0.3 micrometers.

4. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: In step S1, the low-Z foam has a cylindrical structure, the sample has a semi-circular plate structure, and the diameter of the low-Z foam and the sample is greater than the diameter of the nanosecond laser spot.

5. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: The low-Z foam block is a hydrocarbon or boron foam.

6. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: In step S3, the X-ray backlight source is generated by the interaction of one or more laser beams with a high-Z material, wherein the laser power density is greater than 1×10⁻⁶. 14 W / cm 2 .

7. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: The beam splitter is a crystal or a grating.

8. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: In step S3, time resolution is controlled by a pulsed laser driving the backlight material, and the pulse width of the pulsed laser is less than 200 ps; or time resolution is achieved by recording with a time resolution device.

9. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 1, characterized in that: In step S3, spatial resolution is achieved using a point backlight or a spatial resolution slit, wherein the width of the spatial resolution slit is 50-200 micrometers.

10. The method for generating high-temperature, high-density plasma and measuring radiation opacity according to claim 2, characterized in that: In step S2, the synchronization deviation of the laser beams on both sides of the multilayer sample target needs to be controlled within ±100 picoseconds, and the total energy deviation needs to be controlled within 10%; the center of the focal spot of the multi-path laser superposition on each side needs to be controlled within ±100 micrometers.

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