The same substance in nature has the ability to radically vary its properties depending on temperature and pressure. An excellent example of this is water, which exists in the form of solid ice, liquid and vapor. These are three aggregate states of this substance, which has the chemical formula H 2 O. Other substances under natural conditions are capable of changing their characteristics in a similar way. But besides those listed, there is another state of aggregation in nature - plasma. It is quite rare in earthly conditions and endowed with special qualities.
Molecular structure
What do the 4 states of matter in which matter resides depend on? From the interaction of the elements of the atom and the molecules themselves, endowed with the properties of mutual repulsion and attraction. These forces are self-compensating in the solid state, where the atoms are arranged geometrically correctly, forming a crystal lattice. At the same time, the material object is capable of maintaining both of the above-mentioned qualitative characteristics: volume and shape.
But as soon as the kinetic energy of the molecules increases, moving chaotically, they destroy the established order, turning into liquids. They have fluidity and are characterized by the absence of geometric parameters. But at the same time, this substance retains its ability not to change the total volume. In the gaseous state, mutual attraction between molecules is completely absent, so the gas has no shape and has the possibility of unlimited expansion. But the concentration of the substance drops significantly. The molecules themselves do not change under normal conditions. This is the main feature of the first 3 of the 4 states of matter.
Transformation of states
The process of transforming a solid into other forms can be carried out by gradually increasing the temperature and varying the pressure. In this case, transitions will occur abruptly: the distance between molecules will noticeably increase, intermolecular bonds will be destroyed with a change in density, entropy, and the amount of free energy. It is also possible that a solid will be transformed directly into a gaseous form, bypassing intermediate stages. It is called sublimation. Such a process is quite possible under normal earthly conditions.
But when temperature and pressure indicators reach critical levels, the internal energy of the substance increases so much that electrons, moving at breakneck speed, leave their intra-atomic orbits. In this case, positive and negative particles are formed, but their density in the resulting structure remains almost the same. Thus, plasma arises - a state of aggregation of a substance that is, in fact, a gas, fully or partially ionized, the elements of which are endowed with the ability to interact with each other over long distances.
High temperature plasma of space
Plasma, as a rule, is a neutral substance, although it consists of charged particles, because the positive and negative elements in it, being approximately equal in quantity, compensate each other. This state of aggregation under normal terrestrial conditions is less common than others mentioned earlier. But despite this, most cosmic bodies consist of natural plasma.
An example of this is the Sun and other numerous stars of the Universe. Temperatures there are fantastically high. After all, on the surface of the main body of our planetary system they reach 5,500°C. This is more than fifty times higher than the parameters required for water to boil. In the center of the fire-breathing ball, the temperature is 15,000,000°C. It is not surprising that gases (mainly hydrogen) are ionized there, reaching the aggregate state of plasma.
Low temperature plasma in nature
The interstellar medium that fills galactic space also consists of plasma. But it differs from its high-temperature variety described earlier. Such a substance consists of ionized matter resulting from radiation emitted by stars. This is low temperature plasma. In the same way, the sun's rays, reaching the limits of the Earth, create the ionosphere and the radiation belt located above it, consisting of plasma. The differences are only in the composition of the substance. Although all the elements presented in the periodic table can be in a similar state.
Plasma in the laboratory and its application
According to the laws, it can be easily achieved under the conditions familiar to us. When conducting laboratory experiments, a capacitor, diode and resistance connected in series are sufficient. Such a circuit is connected to a current source for a second. And if you touch a metal surface with wires, then the particles of it itself, as well as the vapor and air molecules located nearby, are ionized and find themselves in the aggregate state of plasma. Similar properties of matter are used to create xenon and neon screens and welding machines.
Plasma and natural phenomena
Under natural conditions, plasma can be observed in the light of the Northern Lights and during a thunderstorm in the form of ball lightning. Modern physics has now provided an explanation for some natural phenomena that were previously attributed mystical properties. Plasma, which forms and glows at the ends of tall and sharp objects (masts, towers, huge trees) under a special state of the atmosphere, was taken centuries ago by sailors as a harbinger of good luck. That is why this phenomenon was called “St. Elmo’s Fire.”
Seeing a corona discharge in the form of luminous tassels or beams during a thunderstorm in a storm, travelers took this as a good omen, realizing that they had avoided danger. It is not surprising, because objects rising above the water, suitable for “signs of a saint,” could indicate the approach of a ship to the shore or prophesy a meeting with other ships.
Nonequilibrium plasma
The above examples eloquently demonstrate that it is not necessary to heat a substance to fantastic temperatures in order to achieve the plasma state. For ionization, it is enough to use the force of an electromagnetic field. At the same time, the heavy constituent elements of matter (ions) do not acquire significant energy, because the temperature during this process may well not exceed several tens of degrees Celsius. Under such conditions, light electrons, breaking away from the main atom, move much faster than more inert particles.
Such cold plasma is called nonequilibrium. In addition to plasma TVs and neon lamps, it is also used in water and food purification, and is used for disinfection for medical purposes. In addition, cold plasma can help accelerate chemical reactions.
Principles of use
An excellent example of how artificially created plasma is used for the benefit of humanity is the manufacture of plasma monitors. The cells of such a screen are endowed with the ability to emit light. The panel is a kind of “sandwich” of glass sheets located close to each other. Between them are placed boxes with a mixture of inert gases. They can be neon, xenon, argon. And blue, green, and red phosphors are applied to the inner surface of the cells.
Conductive electrodes are connected outside the cells, between which a voltage is created. As a result, an electric field arises and, as a result, gas molecules are ionized. The resulting plasma emits ultraviolet rays, which are absorbed by phosphors. Due to this, the phenomenon of fluorescence occurs through the photons emitted. Due to the complex combination of rays in space, a bright image of a wide variety of shades appears.
Plasma horrors
This form of matter takes on a deadly appearance during a nuclear explosion. Plasma in large volumes is formed during this uncontrolled process, releasing a huge amount of different types of energy. resulting from the activation of the detonator, it bursts out and heats the surrounding air to gigantic temperatures in the first seconds. At this point, a deadly fireball appears, growing at an impressive speed. The visible area of the bright sphere is increased by ionized air. Clots, puffs and jets of explosion plasma form a shock wave.
At first, the luminous ball, advancing, instantly absorbs everything in its path. Not only human bones and tissues turn into dust, but also solid rocks, and even the most durable artificial structures and objects are destroyed. Armored doors to safe shelters do not save you; tanks and other military equipment are crushed.
Plasma in its properties resembles a gas in that it does not have a specific shape and volume, as a result of which it is capable of expanding indefinitely. For this reason, many physicists express the opinion that it should not be considered a separate state of aggregation. However, its significant differences from just hot gas are obvious. These include: the ability to conduct electric currents and exposure to magnetic fields, instability and the ability of constituent particles to have different speeds and temperatures, while collectively interacting with each other.
The times when plasma was associated with something unreal, incomprehensible, fantastic are long gone. These days this concept is actively used. Plasma is used in industry. It is most widely used in lighting technology. An example is gas-discharge lamps that illuminate streets. But it is also present in fluorescent lamps. It also exists in electric welding. After all, a welding arc is a plasma generated by a plasma torch. Many other examples can be given.
Plasma physics is an important branch of science. Therefore, it is worth understanding the basic concepts related to it. This is what our article is dedicated to.
Definition and types of plasma
What is given in physics is quite clear. Plasma is a state of matter when the latter contains a significant (comparable to the total number of particles) number of charged particles (carriers) capable of moving more or less freely within the substance. The following main types of plasma in physics can be distinguished. If the carriers belong to particles of the same type (and particles of the opposite sign of charge, neutralizing the system, do not have freedom of movement), it is called one-component. In the opposite case, it is two- or multi-component.
Plasma Features
So, we have briefly described the concept of plasma. Physics is an exact science, so you can’t do without definitions. Let us now talk about the main features of this state of matter.
In physics the following. First of all, in this state, under the influence of already small electromagnetic forces, a movement of carriers occurs - a current that flows in this way until these forces disappear due to the screening of their sources. Therefore, the plasma eventually goes into a state where it is quasi-neutral. In other words, its volumes larger than a certain microscopic value have zero charge. The second feature of plasma is associated with the long-range nature of the Coulomb and Ampere forces. It lies in the fact that movements in this state, as a rule, are collective in nature, involving a large number of charged particles. These are the basic properties of plasma in physics. It would be useful to remember them.
Both of these features lead to the fact that plasma physics is unusually rich and diverse. Its most striking manifestation is the ease of occurrence of various types of instabilities. They are a serious obstacle complicating the practical use of plasma. Physics is a science that is constantly evolving. Therefore, one can hope that over time these obstacles will be eliminated.
Plasma in liquids
Moving on to specific examples of structures, we begin by considering plasma subsystems in condensed matter. Among liquids, one should first of all mention - an example that corresponds to the plasma subsystem - a single-component plasma of electron carriers. Strictly speaking, the category of interest to us should include electrolyte liquids in which there are carriers - ions of both signs. However, for various reasons, electrolytes are not included in this category. One of them is that the electrolyte does not contain light, mobile carriers such as electrons. Therefore, the above plasma properties are much less pronounced.
Plasma in crystals
Plasma in crystals has a special name - solid-state plasma. Although ionic crystals have charges, they are immobile. That's why there is no plasma there. In metals there are conductivities that make up a one-component plasma. Its charge is compensated by the charge of immobile (more precisely, unable to move over long distances) ions.
Plasma in semiconductors
Considering the basics of plasma physics, it should be noted that in semiconductors the situation is more diverse. Let us briefly describe it. Single-component plasma in these substances can arise if appropriate impurities are introduced into them. If impurities easily give up electrons (donors), then n-type carriers - electrons - appear. If impurities, on the contrary, easily select electrons (acceptors), then p-type carriers appear - holes (empty spaces in the electron distribution), which behave like particles with a positive charge. A two-component plasma, formed by electrons and holes, arises in semiconductors in an even simpler way. For example, it appears under the influence of light pumping, which throws electrons from the valence band into the conduction band. Note that under certain conditions, electrons and holes attracted to each other can form a bound state similar to a hydrogen atom - an exciton, and if the pumping is intense and the density of excitons is high, then they merge together and form a drop of electron-hole liquid. Sometimes this state is considered a new state of matter.
Gas ionization
The examples given referred to special cases of the plasma state, and plasma in its pure form is called Many factors can lead to its ionization: electric field (gas discharge, thunderstorm), light flux (photoionization), fast particles (radiation from radioactive sources, cosmic rays, which were discovered by increasing the degree of ionization with height). However, the main factor is the heating of the gas (thermal ionization). In this case, the electron is separated from the collision with the latter by another gas particle having sufficient kinetic energy due to the high temperature.
High and low temperature plasma
The physics of low-temperature plasma is something we come into contact with almost every day. Examples of such a state are flames, matter in a gas discharge and lightning, various types of cold cosmic plasma (iono- and magnetospheres of planets and stars), working substance in various technical devices (MHD generators, burners, etc.). Examples of high-temperature plasma are the substance of stars at all stages of their evolution, except for early childhood and old age, the working substance in controlled thermonuclear fusion installations (tokamaks, laser devices, beam devices, etc.).
Fourth state of matter
A century and a half ago, many physicists and chemists believed that matter consisted only of molecules and atoms. They are combined into combinations that are either completely disordered or more or less ordered. It was believed that there were three phases - gaseous, liquid and solid. Substances take them under the influence of external conditions.
However, at present we can say that there are 4 states of matter. It is plasma that can be considered new, the fourth. Its difference from condensed (solid and liquid) states is that, like a gas, it does not have not only shear elasticity, but also a fixed intrinsic volume. On the other hand, plasma is related to the condensed state by the presence of short-range order, i.e., the correlation of the positions and composition of particles adjacent to a given plasma charge. In this case, such a correlation is generated not by intermolecular forces, but by Coulomb forces: a given charge repels charges of the same name as itself and attracts charges of the same name.
Plasma physics was briefly reviewed by us. This topic is quite extensive, so we can only say that we have covered its basics. Plasma physics certainly deserves further consideration.
Thousands of years of intensive development, research into life and nature have led man to the knowledge of the four states of matter. Plasma turned out to be the most mysterious of them. From the moment when man first discovered its existence, the research of plasma and its practical application have advanced by leaps and bounds. Today's promising science, plasma chemistry, arose and began to actively develop.
Even in the times of Ancient Greece, the scientist Aristotle knew that all bodies consist of four lower elements: earth, water, air and fire. Today these concepts have changed their names, but not their meaning. Indeed, everyone knows that matter can exist in four states: solid, liquid, gaseous and plasma.
The fourth state of matter was discovered by W. Crookes in 1879 and called “plasma” by I. Langmuir in 1928.
Plasma (from the Greek plasma - fashioned, shaped), partially or completely ionized gas, in which the densities of positive and negative charges are almost the same.
Plasma is a gas consisting of positively and negatively charged particles in such a ratio that their total charge is zero. Freely moving charged particles can carry electric current, therefore plasma is a gas that has electrical conductivity. Compared to known conductors, in particular metal electrolytes, plasma is thousands of times lighter.
There is no difference in some respects between gases and plasma. Plasma obeys gas laws and behaves like a gas in many respects.
An important feature of plasma is the chaotic movement of particles inherent in gas, which can be ordered in plasma. Under the influence of an external magnetic or electric field, it is possible to give direction to the movement of plasma particles. Consequently, plasma can be thought of as a fluid medium that has the property of conducting electric current.
The concept of plasma, or the plasma state of matter, covers both hot and cold gases that have luminescence and electrical conductivity. There are two types of plasma: isometric, which occurs at a gas temperature high enough for strong thermal ionization, and gas-discharge, which is formed during electrical discharges in gases.
In an isometric plasma, the average kinetic energy of particles: electrons, ions, neutral and excited atoms and molecules is the same. In thermal equilibrium with the environment, such a plasma can exist indefinitely. Gas-discharge plasma is stable only if there is an electric field in the gas that accelerates electrons. The temperature of the gas-discharge plasma is higher than the temperature of the neutral gas. Thus, the plasma state is unstable, and when the electric field ceases, the gas-discharge plasma disappears within a fraction of a second, namely 10-5 and 10-7 seconds, since deionization of gases occurs during this period. Consequently, plasma is, on the one hand, a state of gas and, on the other, a mixture of several gases. It consists of normal molecules, free electrons, ions and photons. The collection of particles of each kind forms its own gas, consisting of neutral molecules, electrons, ions and photons. All these gases taken together form what is called plasma.
Plasma arises as a result of the ionization of molecules: when two particles of molecules with high energy collide, when molecules collide with electrons or ions, when molecules are exposed to photons. All these processes are reversible, since recombination processes occur in the plasma - restoration of the neutral state. In practice, plasma can be formed when a fire burns, when electric current is passed through gas, at elevated temperatures, etc.
According to today's concepts, the phase state of most of the matter (about 99.9% by mass) in the Universe is plasma. All stars are made of plasma, and even the space between them is filled with plasma, albeit very rarefied. For example, the planet Jupiter has concentrated in itself almost all the matter of the solar system, which is in a “non-plasma” state (liquid, solid and gaseous). At the same time, the mass of Jupiter is only about 0.1% of the mass of the Solar System, and its volume is even less: only 10–15%. In this case, the smallest particles of dust that fill outer space and carry a certain electric charge can collectively be considered as a plasma consisting of superheavy charged ions.
Plasma has various properties. The main ones are:
- 1. Electrical conductivity is the main property of plasma. Another property is associated with electrical conductivity, namely glow, as a result of the excitation of molecules. The internal energy of plasma is equal to 3 cal/degree * mol for a monatomic gas, and 12 cal/degree * mol for polyatomic molecules, such as benzene. For the plasma state, the heat capacity is 100-200 cal/degree - mole, i.e. 40-50 times more than that of gases. The large heat capacity is explained by the fact that when a substance transitions from a normal state to a plasma state, part of the energy is spent on ionization. This energy, as we see, is quite large.
- 2. Plasma has a specific movement. It is caused by the presence of a large number of charges that determine the electrical conductivity of the plasma, which leads to a new motion of the plasma, which is not present in any of the other states of aggregation. As is known, in non-ionized systems it occurs under the influence of gravity, inertia, elasticity, and here - under the influence of magnetic and electrical forces. The random movement of electrons and ions leads to the fact that the density of equally charged particles in some areas becomes greater or lesser, as a result of which the charge intensity in some areas either increases or decreases, which causes the movement of positively charged particles towards more intense charges of negative particles. As a result of this movement, pendulum-type oscillations arise, since the movement of a negatively charged field to a positive one, in turn, causes new areas with different densities of charges of the same sign, i.e., waves of positive and negative electricity arise.
- 3. One of the most important properties of plasma is the possibility of the occurrence of electromagnetic oscillations in an extremely wide range under the influence of movement occurring in the plasma itself or under the influence of electric current flowing in the plasma. In the presence of an external strong magnetic field, the plasma begins to move in a direction perpendicular to the current, which makes it possible, acting by an electromagnetic field, to close the motion of the plasma in a circle.
This property of plasma is very important for obtaining high temperatures.
Nuclear synthesis
It is believed that the reserves of chemical fuel will last humanity for several decades. Proven reserves of nuclear fuel are also limited. Controlled thermonuclear reactions in plasma can save humanity from energy starvation and become an almost inexhaustible source of energy.
1 liter of ordinary water contains 0.15 ml of heavy water (D2O). When deuterium nuclei fuse, 0.15 ml of D2O releases the same amount of energy as is produced by the combustion of 300 liters of gasoline. Tritium practically does not exist in nature, but it can be obtained by bombarding an n isotope of lithium with neutrons.
The nucleus of a hydrogen atom is nothing more than a proton p. The deuterium nucleus also contains one more neutron, and the tritium nucleus contains two neutrons. Deuterium and tritium can react with each other in ten different ways. But the probabilities of such reactions sometimes differ by hundreds of trillions of times, and the amount of energy released by 10-15 times. Only three of them are of practical interest.
If all nuclei in a certain volume react simultaneously, energy is released instantly. A thermonuclear explosion occurs. In a reactor, the synthesis reaction must proceed slowly.
Controlled thermonuclear fusion has not yet been achieved, but it promises considerable benefits. The energy released during thermonuclear reactions per unit mass of fuel is millions of times higher than the energy of chemical fuel and, therefore, hundreds of times cheaper. In thermonuclear energy there is no release of combustion products into the atmosphere or radioactive waste. Finally, an explosion has been ruled out at the thermonuclear power plant.
During fusion, the bulk of the energy (more than 75%) is released in the form of kinetic energy of neutrons or protons. If you slow down the neutrons in a suitable substance, it heats up; The resulting heat can be easily converted into electrical energy. The kinetic energy of charged particles - protons - is converted directly into electricity.
In a fusion reaction, the nuclei must combine, but they are positively charged and, therefore, according to Coulomb's law, they repel. To overcome repulsive forces, even deuterium and tritium nuclei, which have the smallest charge (Z. = 1), require an energy of about 10 or 100 keV. It corresponds to a temperature of the order of 108-109 K. At such temperatures, any substance is in a state of high-temperature plasma.
From the standpoint of classical physics, a fusion reaction is impossible, but here the purely quantum tunneling effect comes to the rescue. It is calculated that the ignition temperature, starting from which the energy release exceeds its loss, for the deuterium-tritium (DT) reaction is approximately 4.5x107 K, and for the deuterium-deuterium (DD) reaction - about 4x108 K. Naturally, the DT reaction is preferable. The plasma is heated by electric current, laser radiation, electromagnetic waves and other methods. But not only high temperature is important.
The higher the concentration, the more often the particles collide with each other, so it might seem that high-density plasma is better for carrying out fusion reactions. However, if 1 cm 3 of plasma contained 1019 particles (the concentration of molecules in a gas under normal conditions), the pressure in it at temperatures of thermonuclear reactions would reach about 106 atm. No structure can withstand such pressure, and therefore the plasma must be rarefied (with a concentration of about 1015 particles per 1 cm3). In this case, particle collisions occur less frequently, and to maintain the reaction it is necessary to increase the time they remain in the reactor, or retention time. This means that in order to carry out a thermonuclear reaction, it is necessary to consider the product of the concentration of plasma particles and the time of their retention. For DD reactions, this product (the so-called Lawson criterion) is equal to 1016 s/cm 3, and for the DT reaction - 1014 s/cm 3.
The word "plasma" has many meanings, including a physical term. So, what is plasma in physics?
Plasma is an ionized gas that is formed by neutral molecules and charged particles. This gas is ionized - at least one electron is separated from the shell of its atoms. A distinctive feature of this environment can be called its quasi-neutrality. Quasineutrality means that among all charges in a unit volume of plasma, the number of positive ones is equal to the number of negative ones.
We know that a substance can be gaseous, liquid or solid - and these states, called aggregate states, are capable of flowing into one another. So, plasma is considered the fourth state of aggregation in which a substance can exist.
So, plasma is distinguished by two main properties - ionization and quasi-neutrality. We will talk about its other features further, but first we will pay attention to the origin of the term.
Plasma: history of definition
Otto von Guericke began researching discharges in 1972, but over the next two and a half centuries, scientists could not identify the special properties and distinctive features of ionized gas.
Irving Langmuir is considered the author of the term “plasma” as a physical and chemical definition. The scientist conducted experiments with partially ionized plasma. In 1923, he and another American physicist Tonks proposed the term itself.
Plasma physics originated between 1922-1929.
The word "plasma" is Greek in origin and means a plastic sculpted figure.
What is plasma: properties, forms, classification
If a substance is heated, it will become gaseous upon reaching a certain temperature. If heating is continued, the gas will begin to disintegrate into its constituent atoms. Then they turn into ions: this is plasma.
There are different forms of this state of matter. Plasma manifests itself in terrestrial conditions in lightning discharges. It also forms the ionosphere, a layer in the upper atmosphere. The ionosphere appears under the influence of ultraviolet radiation and makes it possible to transmit radio signals over long distances.
There is much more plasma in the Universe. The baryonic matter of the Universe is almost entirely in the plasma state. Plasma forms stars, including the Sun. Other forms of plasma found in space are interstellar nebulae and the solar wind (a stream of ionized particles coming from the Sun).
In nature, in addition to lightning and the ionosphere, plasma exists in the form of such interesting phenomena as St. Elmo's lights and the Northern Lights.
There is artificial plasma - for example, in fluorescent and plasma lamps, in electric arcs of arc lamps, etc.
Plasma classification
Plasmas are:
- ideal, imperfect;
- high-, low-temperature;
- nonequilibrium and equilibrium.
Plasma and gas: comparison
Plasma and gas are similar in many ways, but there are significant differences in their properties. For example, gas and plasma are different in electrical conductivity - gas has low values for this parameter, while plasma, on the contrary, has high values. Gas consists of similar particles, plasma - of different properties - charge, speed of movement, etc.
What is plasma - an unusual gas
Since childhood, we have known several states of aggregation of substances. Let's take water for example. Its usual state is known to everyone - liquid, it is distributed everywhere: rivers, lakes, seas, oceans. The second state of aggregation is gas. We don't see him often. The easiest way to achieve a gaseous state in water is to boil it. Steam is nothing more than the gaseous state of water. The third state of aggregation is a solid body. We can observe a similar case, for example, in the winter months. Ice is frozen water, and there is a third state of aggregation.
This example clearly shows that almost any substance has three states of aggregation. For some it is easy to achieve, for others it is more difficult (special conditions are required).
But modern physics identifies another, independent state of matter - plasma.
Plasma is an ionized gas with equal densities of both positive and negative charges. As you know, when strongly heated, any substance passes into the third state of aggregation - gas. If we continue to heat the resulting gaseous substance, the output will be a substance with a sharply increased process of thermal ionization; the atoms that make up the gas disintegrate to form ions. This condition can be observed with the naked eye. Our Sun is a star, like millions of other stars and galaxies in the universe, there is nothing more than high-temperature plasma. Unfortunately, on Earth, plasma does not exist under natural conditions. But we can still observe it, for example, a flash of lightning. In laboratory conditions, plasma was first obtained by passing high voltage through a gas. Today, many of us use plasma in everyday life - these are ordinary gas-discharge fluorescent lamps. On the streets one can often see neon advertising, which is nothing more than low-temperature plasma in glass tubes.
In order to move from a gaseous state to plasma, the gas must be ionized. The degree of ionization directly depends on the number of atoms. Another condition is temperature.
Until 1879, physics described and was guided by only three states of matter. Until the English scientist, chemist and physicist William Crookes began conducting experiments to study the conductivity of electricity in gases. His discoveries include the discovery of the element Thalium, the production of Helium in laboratory conditions and, of course, the first experiments with the production of cold plasma in gas-discharge tubes. The familiar term “plasma” was used for the first time in 1923 by the American scientist Langmuir, and later by Tonkson. Until this time, “plasma” meant only the colorless component of blood or milk.
Today's research shows that, contrary to popular belief, about 99% of all matter in the universe is in the plasma state. All stars, all interstellar space, galaxies, nebulae, the solar fan are typical representatives of plasma.
On earth we can observe such natural phenomena as lightning, northern lights, “St. Elmo's fire”, the Earth's ionosphere and, of course, fire.
Man also learned to use plasma for his own benefit. Thanks to the fourth state of matter, we can use gas-discharge lamps, plasma TVs, electric arc welding, and lasers. We can also observe plasma phenomena during a nuclear explosion or the launch of space rockets.
One of the priority research in the direction of plasma can be considered the reaction of thermonuclear fusion, which should become a safe replacement for nuclear energy.
According to the classification, plasma is divided into low-temperature and high-temperature, equilibrium and nonequilibrium, ideal and non-ideal.
Low-temperature plasma is characterized by a low degree of ionization (about 1%) and a temperature of up to 100 thousand degrees. This is why plasma of this kind is often used in various technological processes (applying a diamond film to a surface, changing the wettability of a substance, ozonating water, etc.).
High-temperature or “hot” plasma has almost 100% ionization (this is precisely the state that is meant by the fourth state of aggregation) and a temperature of up to 100 million degrees. In nature, these are stars. Under terrestrial conditions, it is high-temperature plasma that is used for thermonuclear fusion experiments. A controlled reaction is quite complex and energy-consuming, but an uncontrolled reaction has proven itself to be a weapon of colossal power - a thermonuclear bomb tested by the USSR on August 12, 1953.
But these are extremes. Cold plasma has firmly taken its place in human life; useful controlled thermonuclear fusion is still a dream; weapons are actually not applicable.
But in everyday life, plasma is not always equally useful. There are sometimes situations in which plasma discharges should be avoided. For example, during any switching processes we observe a plasma arc between the contacts, which urgently needs to be extinguished.