Plasma

[děng lí zǐ tǐ]

Physical terms

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synonym plasma (Physical term) generally refers to plasma

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

etc. Ions Plasma, also called plasma, is composed of Electronics Dispossessed atom And atomic group quilt ionization The ionized gas like substance composed of positive and negative ions generated after, and the macro electrically neutral ionized gas with a scale larger than Debye length, its movement is mainly dominated by the electromagnetic force, and shows a significant collective behavior. It widely exists in universe It is often regarded as removing solid, liquid and gas, material The fourth state of existence. Plasma is a very good Conductor The plasma can be captured, moved and accelerated by using the ingeniously designed magnetic field. Plasma physics The development of GIS provides new technologies and processes for the further development of materials, energy, information, environmental space, space physics, geophysics and other sciences.

Plasma is different from solid 、 liquid and Gas The fourth state of matter. Matter is composed of molecules, and molecules are composed of atoms. Atoms are composed of positively charged atomic nuclei and negatively charged electrons surrounding them. When heated to a high enough temperature or for other reasons, the outer electrons break away from the atomic nucleus and become free electrons, just like the students running to the playground after class. When electrons leave the nucleus, this process is called "ionization". At this time, the matter becomes a uniform "paste" composed of positively charged atomic nuclei and negatively charged electrons, so it is jokingly called plasma. The total amount of positive and negative charges in these plasma is equal, so it is nearly electrically neutral, so it is called plasma.

Chinese name: Plasma
Foreign name: plasma

Category: physics
Also called: Plasma

catalog

seven nuclear fusion
eight Scientific research contribution

constitute

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The seemingly "mysterious" plasma is actually universe A common substance in sunlight 、 fixed star 、 lightning There are plasmas in all of them, which account for 99% of the whole universe. People have mastered and utilized in the 21st century electric field And magnetic field to control plasma. The most common plasma is high-temperature ionized gas, such as the luminous gas in arc, neon lamp and fluorescent lamp, as well as lightning, aurora, etc. The electron gas in metal, the carrier in semiconductor and electrolyte solution can also be regarded as plasma. On the earth, plasma matter is far less than solid, liquid and gas matter. In the universe, plasma is the main form of matter, accounting for more than 99% of the total amount of matter in the universe. For example, stars (including the sun), interstellar matter and the ionosphere around the earth are all plasmas. In order to study the generation and properties of plasma to clarify the motion law of plasma in nature and use it to serve mankind, magnetohydrodynamics and plasma dynamics have been formed in the past three to four decades under the promotion of astrophysics, space physics, especially nuclear fusion research.

Plasma generator

Plasma consists of ions, electrons and non ionized Neutral particle The whole is in a neutral material state. Plasma can be divided into two types: high temperature and low temperature plasma 。 Plasma temperature is expressed in terms of electron temperature and ion temperature, which are called high-temperature plasma; If it is not equal, it is called low-temperature plasma. Low temperature plasma is widely used in various production fields. For example: Plasma TV ， Waterproof coating on baby diaper surface ， Increase the barrier of beer bottle 。 More importantly Computer chip The application of etching in makes the Internet era a reality.

High temperature plasma Only when the temperature is high enough. Stars constantly emit such plasmas, which make up 99% of the universe. low temperature plasma Is on normal atmospheric temperature The plasma (although the temperature of the electrons is very high) occurs under. Low temperature plasma can be used for oxidation , denaturation and other surface treatment or organic compound and Inorganic Precipitation coating treatment shall be carried out on the.

Substance form of plasma

Plasma Plasma is a free electron And electrification Ions It is the material form of the main component and widely exists in universe It is often regarded as the fourth state of matter, called plasma state, or "super gas state", also known as "plasma". Plasma has high conductivity , and electromagnetic field Strongly existing coupling effect. Plasma is composed of Krux Discovered in 1879, American scientists in 1928 Owen Langmuir And Tonks introduced the word "plasma" for the first time physics , used to describe the material form in the gas discharge tube [1] 。 Strictly speaking, plasma is characterized by high potential energy The total charge of the plasma is still neutral electric field Or the high kinetic energy of the magnetic field knocks out the electrons in the outer layer, and the electrons are no longer bound Nucleus And become free electrons with high energy and high kinetic energy.

Plasma is the fourth state of matter, namely ionized "gas", which presents highly excited unstable states, including Ions (having different symbols and charges), electrons, atoms, and molecules. In fact, people are not new to plasma manifestation. stay nature In, the bright flame and brightness are dazzling lightning , and gorgeous aurora And so on are the results of plasma action. For the whole universe, almost 99.9% of the matter exists in the form of plasma, such as fixed star And interplanetary space are composed of plasma. Use manual methods, such as nuclear fusion 、 Nuclear fission 、 glow discharge And various discharges can produce plasma. The internal structure of a molecule or atom is mainly composed of electrons and Nucleus form. In general, that is, the first three forms of the above matter, the relationship between the electron and the nucleus is relatively fixed, that is, the electron exists in different energy levels Nuclear field Around, its potential energy or kinetic energy not big.

When the temperature of ordinary gas rises Thermal movement It intensifies, causing strong collisions between particles. A large number of electrons in atoms or molecules are knocked off. When the temperature reaches one million to one hundred million, all gas atoms are ionized. The total negative charge of ionized free electrons is equal to the total positive charge of positive ions. This highly ionized, macroscopically neutral gas is called plasma.

Plasma and ordinary gas have different properties. Ordinary gas is composed of molecules, and the interaction between molecules is short-range force. Only when molecules collide, the interaction between molecules has obvious effect, which is theoretically described by molecular motion theory. In plasma Coulomb force Is a long-range force, Coulomb force The effect of is far more than the possible local short-range collision effect of charged particles. When charged particles in the plasma move, they can cause positive charges or negative charge Local concentration, generating electric field; The directional movement of the charge causes a current, producing a magnetic field. Electric and magnetic fields will affect the movement of other charged particles thermal radiation and heat conduction ； Plasma can be magnetic field Constrain to make gyratory motion, etc. These characteristics of plasma make it different from ordinary gas, which is called the fourth state of matter.

stay universe Plasma is the most important normal state of matter. Space research, space development, and satellites Aerospace 、^[1] energy Such new technologies will enter a new era with the research of plasma.^[2]

History

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Research on gas discharge since the 19th century; The research on astrophysics and space physics in the 20th century began in the middle of the 19th century; The research on controlled thermonuclear fusion began around 1950; as well as Low temperature plasma technology Applied research has promoted the development of this discipline from four aspects.

M Faraday And J J. Thomson, J.S.E. Townsend and others successively studied gas discharge Phenomenon, which is actually the initial period of plasma experimental research. In 1879, W Krux Using "Substance Fourth state ”This term is used to describe the ionized gas in the gas discharge tube. The term plasma was first introduced by I. Langmuir of the United States in 1928, and plasma physics was officially introduced. In 1929, L. Tonks and Langmuir of the United States pointed out that electron density The dense wave (i.e. Langmuir wave).

The exploration of space plasma also began at the beginning of the 20th century. In 1902, in order to explain the phenomenon that radio waves can be spread over a long distance, the British, such as O. Harvey, speculated that there was an ionosphere over the earth that could reflect electromagnetic waves. The hypothesis is that E 5. Appleton proved it by experiment. British D R. Hartley (1931) and Appleton (1932) proposed the formula of the refractive index of the ionosphere and obtained the dispersion equation of magnetized plasma. S. Chapman and V C. A. Ferraro believes that the sun will emit high-speed charged particle stream, which will geomagnetic field Surround it and deform it by compression.

Since the 1930s, magnetohydrodynamics and plasma dynamics have been gradually formed. The velocity distribution function of plasma obeys Fokker Planck equation. In 1936, the collision integral form of the collision term caused by the collision of particles in the plasma was given by the Soviet Union's Л. Д. Landau. In 1938, A A. Vlasov proposed the Vlasov equation, that is, the collision free equation without collision terms. Landau collision integral and Vlasov equation marked the beginning of dynamic theory.

In 1942, H. Alvin of Sweden pointed out that when an ideal conductive fluid is in a magnetic field, it will produce shear waves (Alvin waves) propagating along the magnetic field lines. In 1942, S. Chandraseka of India proposed to use the trial particle model to study Relaxation process 。 In 1946 Landau proved that when Langmuir waves propagate, resonant electrons will absorb waves energy Cause wave attenuation, which is called Landau damping 。 Landau's theory has opened up new research fields of wave particle interaction and micro instability in plasma.

From 1935 to 1952, H H. Bogoliubov, M. Born of England and others obtained an unclosed system of equations called BBGKY chain from Liouville theorem. The Vlasov equation can be derived from it, which lays a theoretical foundation for the kinetic theory of plasma.

After 1950, because Britain, the United States, the Soviet Union and other countries began to vigorously study Controlled thermonuclear reaction And promote the vigorous development of plasma physics. The concept of thermonuclear reaction first appeared in 1929, when Atkinson of Britain and Hautmans of Austria proposed that the thermonuclear reaction between hydrogen nuclei in the sun energy It is the source of solar energy, which is a natural self controlled thermonuclear reaction. In 1957, J D. Lawson proposes the realization of controlled thermonuclear reaction energy The condition of gain is the Lawson criterion.

Since the 1950s, a number of experimental devices for controlled fusion have been built, such as the star simulator and magnetic mirror in the United States and the Tokamak in the Soviet Union. These three are magnetic confinement thermonuclear fusion experimental devices. After the 1960s, another group was established inertial confinement fusion Experimental device.

The equilibrium problem of annular magnetically confined plasmas was solved by V D. Shafranov and others. M. Kruska and Shavlanov of the United States derived the most important Plasma instability Criterion of torsional instability. In 1958, I B. Bernstein et al. proposed the energy principle for analyzing macro instability. Transport of plasma in annular magnetic field coefficient First of all, D. Pfielsch of the Federal Republic of Germany and others made a study (1962). They gave the diffusion coefficient in the area with high density, and A A. Galeyev et al. gave the diffusion system dispersion (1967) with relatively small density, which is suitable for the transport process in toroidal magnetically confined plasmas such as Tokamak, and is named as the new classical theory.

Since the Soviet Union launched its first man-made satellite in 1957, many countries have successively launched scientific satellites and space laboratories to obtain a lot of observation and experimental data, which has greatly promoted the development of astrophysics and space plasma physics. In 1959, J A. Van Allen predicted that there was a strong radiation belt over the earth, which was confirmed by future experiments, namely called Van Allen belt. E N. Parker proposed the solar wind model. D A. According to satellite data, authentication It is a radiant star, which is long wave radiation and thermal infrared radiation^[3] 。 The radiation source of the earth radiation is the earth, and its wavelength range is about 4~120 μ m, which is long wave radiation^[3] 。 99% of the radiant energy is concentrated in the wavelength range of more than 3 μ m^[3] 。 The strongest wavelength of earth radiation is about 9.7 μ m^[3] 。

During this period, some low-temperature plasma technologies have been further applied and promoted on the basis of previous gas discharge and arc technologies, such as plasma cutting, welding, spraying MHD power generation , plasma chemistry, plasma metallurgy, and ion propulsion of rockets have all promoted the research on the properties of low-temperature plasma with incomplete ionization.

After 30 years of development, the Institute of Plasma has been engaged in high temperature plasma physics experiment and nuclear fusion engineering technology research Chinese science The Institute of Plasma Physics of the Chinese Academy of Sciences is at the international advanced level and has formed extensive international exchanges and cooperation. It has established stable cooperation and exchange relations with nearly 30 countries and regions in Europe, the United States, Japan, Russia, Australia and other countries and regions. It has carried out many international cooperation projects and become the "Open Laboratory of the Third World Academy of Sciences" and the "World Laboratory Fusion Research Center", It is one of the important units of the ITER China Working Group of the International Controlled Thermonuclear Fusion Program.

Ionic effect

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The ionosphere is composed of the spherical surface of the atmosphere with ions ionized by solar radiation, which is the plasma area, forming layers D, E, F1 and F2 with different ion densities. When the spacecraft returns to the atmosphere, the high temperature caused by friction forms a very dense plasma on the surface of the spacecraft electron density When it is high enough, it will cause Plasma frequency Very high (generally 8MHz), so the communication between ground and spacecraft was blocked, and communication was not resumed until its speed dropped.

Main applications

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When the light hits the metal surface, Two-dimensional light Or plasma will be inspire 。 Plasma can be seen as the connection between photons and electrons.

A mixing principle can be established, when the plasma converted from light propagates on the metal surface (the wavelength of the plasma is much smaller than the wavelength of the original light wave); Plasma can be Two dimensional optical instrument (mirror, waveguide, lens, etc.) processing, the plasma can be converted into light again or electrical signal 。

Plasma

Plasma sensor and Cancer therapeutic apparatus NaomiHalas described how the plasma excites the surface of the small metal layer. The grain shaped particles have great energy spectroscopy The light of the test is Micromolecule Order of magnitude. The electric field ratio of the plasma at the curved tip of the rice particle to the electric field used to excite the plasma field strength Many, and it greatly improves the spectral rate and Accuracy 。 In other words, nanoscale plasma can not only be used for identification, but also can be used to kill cancer cell 。

Plasma microscope Igor Smolyaninov reported that he and his colleagues were able to photograph objects with a spatial resolution of 60 nm (30 nm for practical materials), while laser excitation could only reach 515 nm. In other words, the microscope made with this resolution will be much better than the diffraction method commonly used; And this is far field Microscope -- The light source should not be placed in the range less than the light wavelength. Huge optical polarization and optical transmission: GennadyShvets reports when the surface phonon The microscope is excited by light to make a super prism (lensed by flat material) infrared One twentieth of the wavelength of a light microscope. He and his colleagues can take pictures of the characteristics under the surface of the sample, which they call "huge light transmission". The light that hits the surface is much smaller than the wavelength of ordinary light.

Optical frequency The future of plasma circuit: NaderEngheta supports plasma excited Nanoparticles Can be designed to be of nanometer magnitude capacitance ， resistance , and a sensor (various elements in the circuit).

The circuit can receive radio broadcast (1010Hz) or microwave (1012Hz), while the circuit can reach the optical frequency (1015Hz). This can realize miniaturization and the process of detecting optical signals with nano antennas, Nanowaveguide ， Nanosensor And it is also possible to realize nano computers, nano storage, Nanometer signal And photomolecular interface.

Plasma is mainly used in the following three aspects.

Plasma

① Plasma smelting: it is difficult to use ordinary methods for smelting smelt Materials, such as high melting point zirconium (Zr)、 titanium (Ti)、 tantalum (Ta)、 niobium (Nb)、 vanadium (V)、 tungsten (W) Equal metal; It is also used to simplify the process, for example, to obtain Zr, Mo, Ta and Ti directly from ZrCl, MoS, TaO and TiCl; The hard High melting point Powder, such as Tungsten carbide - cobalt , Mo Co, Mo-Ti-Zr-C and other powder plasma smelting have the advantage of good consistency of product composition and microstructure, which can avoid the pollution of container materials.

② Plasma spraying: the parts of many equipment shall be resistant to wear, corrosion and high temperature, so it is necessary to spray a layer of materials with special performance on its surface. The plasma deposition rapid solidification method can be used to spray the special material powder into the hot plasma to melt, and spray it onto the substrate (parts), so that it can be rapidly cooled and solidified to form a surface layer close to the network structure, which can greatly improve the spraying quality.

③ Plasma welding: it can be used to weld steel Alloy steel ； aluminum 、 copper , titanium, etc. and their alloys. The feature is that the weld is flat and can be reprocessed oxidation Impurities, fast welding speed. It is used for cutting steel, aluminum and their alloys with large cutting thickness.

technology

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Plasma electrical Technically, it refers to an uncharged ionized material with ions, electrons and core particles. Plasma includes almost the same amount of free electron and anode Electronics. In a plasma, the particles have been separated from the core particles. Therefore, when a plasma contains a large number of ions and electrons, it is the best conductor of electricity, and it will be affected by the magnetic field. When the temperature is high, electrons will be separated from the core particles.

Plasma

In recent years, PDP with the support of plasma flat screen technology is really at the height of its power. It is the best candidate for real flat screen TV in the future. In fact, plasma display technology is not a new technology in the 21st century. As early as 1964, the University of Illinois successfully developed a plasma display panel, but then Plasma display It is monochrome. Now plasma flat screen technology is the latest technology, and it is the best choice for high-quality images and large flat screen. The large flat screen can watch TV in any environment. The plasma panel has a series of pixels, and these pixels also contain three secondary pixels, which are red, green and blue. The gas energy in the plasma state is the same as that in each pixel phosphorescence And can produce red, green or blue. such phosphorescence Body and application crt (CRT) device (such as TV sets and ordinary computer monitors) Phosphor It is the same. You can get the rich and dynamic colors you expect from this. Each sub-pixel controlled by an advanced electronic component can produce 1.6 billion different colors. All these mean that you can easily see the best picture on a display screen less than 6 inches thick.

Instability

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Plasma deviation thermodynamic equilibrium The nature of. There are generally two types of methods. One is plasma macroscopic Parameters such as density 、 temperature 、 pressure And other thermodynamic quantities Uniformity The resulting instability changes the overall shape of the plasma, which is called macro instability or Configuration space Instability, available in magnetohydrodynamics (see Plasma physics ）Therefore, it is also called magnetohydrodynamic instability. The other is the deviation of plasma velocity spatial distribution function maxwell Distribution, and the resulting instability is called microcosmic Instability or velocity space instability, available Kinetic theory of plasma Analysis is also called dynamic instability.

Plasma

The instability of plasma (both macroscopic and microscopic) can also cause its displacement kinetic energy Quantity classification. Such as current instability caused by magnetic energy; Exchange instability caused by expansion energy when plasma expands to weak magnetic field region; Drift instability caused by plasma expansion energy generated by density and temperature gradient; Not corresponding to Maxwell distribution or pressure anisotropy free energy The instability of velocity space caused by. Various instabilities in the plasma can lead to charged particle The escape of the plasma or the abnormal increase of the transport coefficient destroy the confinement of the plasma or limit the confinement time. Therefore, studying various instabilities of plasma, clarifying its physical mechanism, and exploring the methods of stabilization have always been a central topic in the research of controlled thermonuclear fusion Plasma physics Important content of.

If the plasma column is only constrained by the angular magnetic field generated by the longitudinal current in it, it will shrink more due to the increase of the inward magnetic pressure at the contraction and expand more due to the decrease of the inward magnetic pressure at the expansion after a slight disturbance, so it is called sausage Sausage instability It can cut off the plasma, add longitudinal magnetic field to resist contraction and expansion, and then stabilize it. If the longitudinal strength electric current If the plasma column is slightly bent when disturbed, the magnetic field at the concave part will increase and the convex part will weaken. The resulting magnetic pressure difference will expand the disturbance and the plasma column will soon bend or even form helical line , this is torsional instability, available Longitudinal magnetic field Make it stable. If the water is above and the oil is below, it will exchange under the action of gravity if there is a slight disturbance. The instability similar to this in the plasma is called exchange instability. The above cases belong to macroscopic Instability.

nuclear fusion

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Nuclear fusion is the main choice to solve the future energy problem. High temperature plasma The purpose of the research is to realize nuclear fusion. Tokamak Type nucleus fusion Research is one of the main fusion research approaches in the world, and also the main discipline direction of the Institute. The Institute has successively built several sets of HT-6B, HT-6M, HT-7 and EAST Tokamak fusion The experimental device and its research system have participated in the international thermonuclear fusion test reactor (ITER) program and research. Plan for the future Built in China Steady state combustion Tokamak The experimental reactor and China's magnetic confinement fusion demonstration reactor will realize the commercialization of pure fusion energy.

In the process of building Tokamak and carrying out plasma physics experiment research, the Institute has developed diagnostics, power supply, microwave, cryogenic, superconducting, vacuum, data acquisition and processing Material Science , safety and environmental protection, electrical physics and precision instrument processing, etc. In high-power power supply, large-scale low-temperature refrigeration, superconducting energy storage High temperature superconductivity The technologies in the development of electrical and physical equipment have been applied to the national economy, and some of them have been industrialized.

Scientific research contribution

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Since the founding of the People's Republic of China, plasma has been responsible for NDRC , Ministry of Science and Technology National Foundation Committee And the Chinese Academy of Sciences. Plasma has built conventional magnet Tokamak device HT-6B and HT-6M and the first circular section in China Superconducting Tokamak Device HT-7; In 2006, the world's first non-circular cross-section all superconducting Tokamak EAST device was independently built in the Plasma Institute, and the successful construction of EAST was internationally recognized fusion It is evaluated by the world as "an outstanding achievement in the world's fusion engineering, an outstanding achievement and an important milestone in the world's fusion energy development", and this major achievement won the honor of 2008 National Science and Technology Progress Award The first prize was selected as "China's Top Ten Scientific and Technological Progress" and "China's Top Ten News of Basic Research" in 2006.

Plasma location and high temperature heat nuclear fusion Plasma physics Plasma theory and experiment, reactor technology, high-power power supply technology Computer automatic control Data acquisition and processing technology, high vacuum technology, low-temperature refrigeration technology, low-temperature superconductivity and High Temperature Superconducting Technology , special material technology, large-scale microwave heating, current drive and other disciplines have achieved outstanding research results, which has accumulated a comprehensive talent team with different disciplines. Multiple sets built Plasma physics Diagnostic system, 2MW wave heating system, 2MW wave driving current system, AC/DC pulse with a total power rate of 200000 kW Power supply system 110kV substation, China's largest 2kW liquid helium refrigeration system, ultra-high vacuum system, 200000 Gaussian Steady state hybrid magnet, advanced computer control and data acquisition and processing system, large superconducting magnet Advanced facilities such as production and testing systems will be built into a comprehensive and systematic advanced platform for plasma physics and fusion engineering and technology research and development.

Ion beam bioengineering is a new research field crossed by physics and biology created by the researchers of the Institute of Plasma Science, and has formed a new interdisciplinary branch - ion beam bioengineering. This subject This paper mainly studies the impact of low-energy ion radiation in nature on evolution and health, and studies the interaction mechanism of ion beam, ray beam and organism based on the precise positioning irradiation platform of ion beam and single ion beam cells. ion beam bioengineering technology Already in Industrial biotechnology , agriculture, environmental health and other fields, and achieved significant social benefits and economic performance , has won important national awards for many times, and has become a "leading team" in this field.

sunlight Energy Materials and Engineering Research has successively undertaken the 973 Program of National Key Basic Research, the Chinese Academy of Sciences Knowledge Innovation Project Many projects, such as dye-sensitized solar cells, photoelectric functional materials and polymer crystallization, have made a number of internationally advanced scientific research achievements, making positive contributions to the development of solar energy with Chinese characteristics.

In combination with the requirements of the development outline for building an innovative country, the Institute has established Low temperature plasma technology Applied research in the fields of environment, new energy, chemical industry, new materials, etc. has made a series of achievements Independent intellectual property rights New and high-tech achievements that can play an important role in the national economy.

etc. Ions Edited and published by 《Plasma Science and Technology》 It is the only English academic journal of plasma in China and has been included in important international databases such as SCI and SA.^[4]

The application of plasma in catalysis mainly focuses on^[5] ：

Methane conversion catalyzed by low-temperature plasma
Oxidation of light alkanes by CO2 under the combined action of plasma catalysis
Low temperature plasma catalytic treatment of waste gas, such as VOCs

In September 2022, a new study jointly participated by researchers from China and Australia found that atmospheric pressure cold plasma can inhibit coronavirus from invading human cells, laying the foundation for developing drugs such as nasal sprays that can prevent coronavirus. Related papers have recently been published in the Australian Journal of Diagnostic Therapy.^[6]

On September 23, 2022, Research team led by Professor Zong Qiugang of School of Earth and Space Sciences, Peking University In an article published in the international academic journal Nature Communication, it is proposed that in space and astroplasm, the cross scale wave particle interaction can lead to rapid energy transport from macro scale to micro scale.^[7]

In 2023, After the star simulator Wendelstein 7-X of the German nuclear fusion device was restarted, the nuclear fusion achieved the experimental goal of 1.3 GJ, the discharge time reached a new optimal value, and the hot plasma could last for 8 minutes.^[8]

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