Plasma is the fourth state of aggregation. Plasma in physics

In a gas discharge there occurs a large number of positive ions due to high efficiency impact ionization, and the concentration of ions and electrons is the same. Such a system of electrons and positive ions distributed with the same concentration is called plasma . The term “plasma” was introduced in 1929 by American physicists I. Langmuir and L. Tonks.

The plasma that appears in a gas discharge is called gas-discharge; it includes a positive column of a glow discharge, a channel of spark and arc discharges.

The positive column represents the so-called non-isothermal plasma. In such a plasma, the average kinetic energies of electrons, ions and neutral molecules (atoms) are different.

Let us recall the relationship between the average kinetic energy of molecules of an ideal gas (the gas pressure in a glow discharge is small, so it can be considered ideal) and temperature

It can be argued that the temperatures of the plasma components are different. So, electron temperature in a glow discharge in neon at a pressure of 3 mm. rt. Art., about 4∙10 4 K, and the temperature of ions and atoms is 400 K, and the temperature of the ions is slightly higher than the atomic temperature.

Plasma in which the equality holds:(where the indices " uh», « And», « A"refers to electrons, ions, atoms) called isothermal . Such plasma occurs during ionization using high temperature (arc burning at atmospheric pressure and above, spark channel); for example, in an ultra-high pressure arc (up to 1000 atm.), the plasma temperature reaches 10,000 K, the plasma temperature at thermonuclear explosion– on the order of several tens of millions of degrees, in the “TOKAMAK” installation for studying thermonuclear reactions – on the order of 7∙10 6 K.

Plasma can arise not only when current passes through a gas. Gas can also be converted into a plasma state by heating it to high temperatures. The inner regions of stars (including the sun) are in a plasma state, the temperatures of which reach 10 8 K (Fig. 8.10).

The long-range Coulomb interaction of charged particles in a plasma leads to a qualitative uniqueness of the plasma, which allows us to consider it special, fourth state of matter.

The most important properties of plasma :

Plasma is the most common state of matter in the Universe. The Sun and other stars are composed of fully ionized, high-temperature plasma. The main source of stellar radiation energy is thermodynamic fusion reactions occurring in the interiors of stars at enormous temperatures. Cold nebulae and the interstellar medium are also in a plasma state. They are low-temperature plasma, ionization of which occurs mainly through photoionization under the influence of ultraviolet radiation from stars. In near-Earth space, weakly ionized plasma is found in the radiation belts and ionosphere of the Earth. The processes occurring in this plasma are associated with such phenomena as magnetic storms, disturbances in long-range radio communications and auroras.

Low-temperature gas-discharge plasma, formed during glow, spark and arc discharges in gases, is widely used in various light sources, in gas lasers, for welding, cutting, melting and other types of metal processing.

The main practical interest in plasma physics is associated with solving the problem of controlled thermonuclear fusion - the process of fusion of light atomic nuclei at high temperatures under controlled conditions. The energy output of the reactor is 10 5 kW/m 3 in the reaction

at a plasma density of 10 5 cm - 3 and a temperature of 10 8 K.

It is proposed to contain high-temperature plasma (1950 USSR, I.E. Tamm, A.D. Sakharov) by a strong magnetic field in a toroidal chamber with magnetic coils, abbreviated as - tokamak. Figure 8.11 shows tokamak circuit: 1 – primary winding of the transformer; 2 – toroidal magnetic field coils; 3 – liner, thin-walled internal chamber for leveling the toroidal electric field; 4 – toroidal magnetic field coils; 5 – vacuum chamber; 6 – iron core (magnetic core).

Currently, as part of the implementation of the world thermonuclear program, latest systems type tokamak. For example, the first Russian spherical tokamak"Globus-M". It is planned to create a large tokamak TM-15 to study plasma configuration control. The construction of the Kazakh tokamak KTM has begun to test thermonuclear energy technologies. Figure 8.12 shows a cross-sectional diagram of the KTM tokamak and its view with a vacuum chamber.

The implementation of a controlled thermonuclear reaction in high-temperature plasma will allow humanity in the future to obtain practically inexhaustible source energy.

Low temperature plasma ( T~ 10 3 K) is used in gas-discharge light sources, gas lasers, thermionic converters of thermal energy into electrical energy. It is possible to create a plasma engine that is effective for maneuvering in outer space and long-term space flights.

Plasma serves as a working fluid in plasma rocket engines and MHD generators.

The motion of plasma in a magnetic field is used in the method of direct conversion of the internal energy of an ionized gas into electrical energy. This method was implemented in magnetohydrodynamic generator(MHD generator), circuit diagram which is shown in Figure 8.13.

Highly heated ionized gas resulting from combustion of fuel and enrichment of combustion products with vapors alkali metals, which contribute to increasing the degree of ionization of the gas, passes through the nozzle and expands in it. In this case, part of the internal energy of the gas is converted into its kinetic energy. In a transverse magnetic field (in Figure 8.9, the field magnetic induction vector is directed beyond the plane of the drawing), positive ions are deflected under the action of Lorentz forces to the upper electrode A, and free electrons go to the bottom electrode TO. When the electrodes are shorted to an external load, there is electricity, directed from the anode A, MHD generator, to its cathode TO.

The properties of plasma to emit electromagnetic waves in the ultraviolet range are used in modern flat-screen plasma TVs. Plasma ionization in a flat screen occurs in a gas discharge. A discharge occurs when gas molecules are bombarded by electrons accelerated by an electric field - an independent discharge. The discharge is maintained at a fairly high electrical potential - tens and hundreds of volts. The most common gas filling for plasma displays is a mixture of inert gases based on helium or neon with the addition of xenon.

The screen of a flat-panel TV or display using gas-discharge elements is made up of a large number of cells, each of which is an independent emitting element. Figure 8.14 shows the design of a plasma cell consisting of a phosphor 1, electrodes 2 that initiate the plasma 5, a dielectric layer (MgO) 3, glass 4, an address electrode 6. The address electrode, together with the main function of a conductor, performs the function of a mirror that reflects half of the light, emitted by the phosphor towards the viewer.

The service life of such a plasma screen is 30 thousand hours.

In flat gas-discharge screens that reproduce color image, three types of phosphors are used, emitting red (R), green (G) and blue (B) light. A flat-screen TV with a screen made of gas-discharge elements contains about a million small plasma cells assembled into triads of RGB pixels ( pixel – picture element).

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 also in lamps daylight she is present. 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 there is significant (comparable with full number particles) the number of charged particles (carriers) capable of moving more or less freely within a 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 of a collective nature, involving big number 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 that makes it difficult practical use 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 structures, let's start 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, according to various reasons electrolytes do not fall into 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 - plasma solid. 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 bound state, similar to a hydrogen atom, is 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 conditions include flames, matter in a gas discharge, and lightning, different kinds cold cosmic plasma (ion- and magnetospheres of planets and stars), working substance in various technical devices(MHD generators, burners, etc.). Examples of high-temperature plasma are the matter of stars at all stages of their evolution, except early childhood and old age, 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.

Plasma is a partially or fully ionized gas in which the densities of positive and negative charges are almost equal. Therefore, in general, plasma is an electrically neutral system.

Determined by the ratio of the number of ionized atoms to their total number

Depending on the degree of ionization, plasma is divided into weakly ionized( - fractions of a percent), partially ionized(- a few percent) and fully ionized( = 100%). The weakly ionized plasma is the ionosphere - the upper layer earth's atmosphere. The Sun and hot stars are in a state of completely ionized plasma. The sun and stars are giant clumps of hot plasma, where the temperature is very high, on the order of 10 6 - 10 7 K. Artificially created plasma varying degrees ionization is plasma in gas discharges and gas-discharge lamps.

The existence of plasma is associated either with the heating of the gas, or with radiation of various kinds, or with the bombardment of the gas by fast charged particles.

A number of plasma properties allow us to consider it as special condition substances. Plasma is the most common state of matter. Plasma exists not only as the substance of stars and the Sun, it fills and space between stars and galaxies. The upper layer of the Earth's atmosphere is also weakly ionized plasma. Plasma particles interact intensively with external electric and magnetic fields: due to their high mobility, charged plasma particles easily move under the influence of electric and magnetic fields. Therefore, any violation of the electrical neutrality of individual regions of the plasma caused by the accumulation of particles with a charge of the same sign quickly disappears. The resulting electric fields move the charged particles until electrical neutrality is restored and the electric field becomes zero.

Between charged plasma particles there are Coulomb forces, decreasing relatively slowly with distance. Each particle interacts immediately with big amount surrounding particles. Due to this, along with chaotic thermal motion, plasma particles can participate in a variety of ordered movements. Various types of oscillations and waves are easily excited in plasma. Plasma conductivity increases as the degree of ionization increases. Electrical and thermal conductivity of fully ionized plasma depend on temperature according to the laws

respectively. At high temperature fully ionized plasma is close to superconductors in its conductivity.

Ionization of atoms of the interstellar medium is carried out by radiation from stars and cosmic rays - streams of fast particles that penetrate the space of the Universe in all directions. In contrast to the hot plasma of stars, the temperature of interstellar plasma is very low.

Control of plasma motion in electrical and magnetic fields is the basis for its use as a working fluid in various engines for the direct conversion of internal energy into electrical energy - plasma sources of electricity, magnetohydrodynamic generators. For spaceships The use of low-power plasma engines is promising. A powerful jet of dense plasma produced in a plasma torch is widely used for cutting and welding metals, drilling wells, accelerating many chemical reactions. Large-scale research is being conducted on the use of high-temperature plasma to create controlled thermonuclear reactions.

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. Distinctive feature This environment can be called 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 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.

Eat different shapes 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 like St. Elmo's Lights, 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, in plasma, on the contrary, are high. Gas consists of similar particles, plasma - of different properties - charge, speed of movement, etc.

In the first three states - solid, liquid and gaseous - electrical and magnetic forces are deeply hidden in the depths of matter. They are entirely used to bind nuclei and electrons into, atoms into and into crystals. The substance in these states is generally electrically neutral. Another thing is plasma. Electric and magnetic forces come to the fore here and determine all its basic properties. Plasma combines the properties of three states: solid (), liquid (electrolyte) and gaseous. From the metal it takes high electrical conductivity, from the electrolyte - ionic conductivity, from the gas - high mobility of particles. And all these properties are intertwined so complexly that plasma turns out to be very difficult to study.

And yet, scientists manage to look into the dazzlingly glowing gas cloud with the help of subtle physical instruments. They are interested in the quantitative and qualitative composition of plasma, the interaction of its parts with each other.

You cannot touch the hot plasma with your hands. It is felt using very sensitive “fingers” - electrodes inserted into the plasma. These electrodes are called probes. By measuring the current flowing to the probe at different voltages, you can find out the degree of concentration of electrons and ions, their temperature and a number of other characteristics of the plasma. (By the way, it’s interesting that even A4 paper, with certain manipulations with it, can also turn into plasma)

The composition of plasma is determined by taking samples of the plasma substance. Special electrodes extract small portions of ions, which are then sorted by mass using an ingenious physical device - a mass spectrometer. This analysis also makes it possible to find out the sign and degree of ionization, that is, negatively or positively, singly or repeatedly ionized atoms.

Plasma can also be felt using radio waves. Unlike ordinary gas, plasma strongly reflects them, sometimes more strongly than metals. This is due to the presence of free electric charges. Until recently, such radio sensing was the only source of information about the ionosphere - a wonderful plasma “mirror” that nature placed high above the Earth. Today the ionosphere is also studied using artificial satellites and high-altitude rockets that take samples of ionospheric matter and analyze it “on the spot”.

Plasma is a very unstable state of matter. Ensure coordinated movement of all its components- a very difficult matter. It often seems that this has been achieved, the plasma is pacified, but suddenly for some reason it is not always known reasons Condensations and rarefactions form in it, strong vibrations arise, and its calm behavior is sharply disrupted.

Sometimes the “play” of electric and magnetic forces in plasma itself comes to the aid of scientists. These forces can form bodies of compact and regular shape from plasma, called plasmoids. The shape of plasmoids can be very diverse. There are rings, and tubes, and double rings, and twisted cords. Plasmoids are quite stable. For example, if you “shoot” two plasmoids towards each other, then upon collision they will fly away from each other, like billiard balls.

The study of plasmoids allows us to better understand the processes occurring with plasma on the gigantic scale of the universe. One of the types of plasmoids - cord - plays very important role in scientists' attempts to create a controlled one. Plasma eaters will apparently also be used in plasma chemistry and metallurgy.

ON EARTH AND IN SPACE

On Earth, plasma is a rather rare state of matter. But already at low altitudes the plasma state begins to predominate. Powerful ultraviolet, corpuscular and x-ray radiation ionizes the air upper layers atmosphere and causes the formation of plasma “clouds” in the ionosphere. The upper layers of the atmosphere are the protective armor of the Earth, protecting all living things from the destructive effects solar radiation. The ionosphere is an excellent mirror for radio waves (with the exception of ultrashort ones), allowing terrestrial radio communications over long distances.

The upper layers of the ionosphere do not disappear at night: the plasma in them is too rarefied for the ions and electrons that appeared during the day to reunite. The further from the Earth, the fewer neutral atoms there are in the atmosphere, and at a distance of one and a half hundred million kilometers there is the colossal clot of plasma closest to us -.

Fountains of plasma constantly fly out of it - sometimes to a height of millions of kilometers - the so-called prominences. Vortexes of slightly less hot plasma—sunspots—move across the surface. The temperature on the surface of the Sun is about 5,500°, the sunspots are 1,000° lower. At a depth of 70 thousand kilometers it is already 400,000°, and even further the temperature of the plasma reaches more than 10 million degrees.

Under these conditions, the nuclei of solar matter atoms are completely exposed. Here, under enormous pressures, thermonuclear reactions of hydrogen nuclei merging and transforming them into nuclei are constantly taking place. The energy released in this case replenishes that which the Sun so generously radiates into space, “heating” and illuminating its entire system of planets.

Stars in the universe are at different stages of development. Some die, slowly turning into cold, non-luminous gas, others explode, throwing huge clouds of plasma into space, which after millions and billions of years reach others in the form of cosmic rays star worlds. There are areas where gravitational forces condense gas clouds, pressure and temperature increase in them until favorable conditions are created for the appearance of plasma and the initiation of thermonuclear reactions - and then new stars flare up. Plasma in nature is in a continuous cycle.

PRESENT AND FUTURE OF PLASMA

Scientists are on the verge of mastering plasma. At the dawn of mankind, the greatest achievement was the ability to create and maintain fire. But today it was necessary to create and preserve for a long time another, much more “highly organized” plasma.

We have already talked about the use of plasma in the household: voltaic arc, fluorescent lamps, gastrons and thyratrons. But what “works” here is a relatively cool plasma. In a voltaic arc, for example, the ion temperature is about four thousand degrees. However, now super-heat-resistant alloys are appearing that can withstand temperatures up to 10-15 thousand degrees. To process them, you need plasma with a higher ion temperature. Its use holds considerable promise for the chemical industry, since many reactions proceed faster the higher the temperature.

To what temperature have you managed to heat the plasma so far? Up to tens of millions of degrees. And this is not the limit. Researchers are already approaching a controlled thermonuclear fusion reaction, during which huge amounts of energy are released. Imagine an artificial sun. And not just one, but several. After all, they will change the climate of our planet and will forever remove humanity’s concern for fuel.

Here are the applications awaiting plasma. In the meantime, research is underway. Large teams of scientists are working hard, bringing closer the day when the fourth state of matter will become as common for us as the other three.