What phenomenon is called a corona discharge. Corona discharge and its characteristics. Grand Hetman Crown Stanislav Zolkiewski
A large detachment of warriors of Ancient Rome was on a night hike. A storm was coming. And suddenly hundreds of bluish lights appeared above the detachment. It was the tips of the spears of the warriors that lit up. It seemed that the iron spears of the soldiers were burning without burning!
In those days, no one knew the nature of the amazing phenomenon, and the soldiers decided that such a radiance on the spears portends their victory. Then this phenomenon was called the fires of Castor and Pollux - after the mythological twin heroes. And later renamed the lights of Elmo - by the name of the church of St. Elmo in Italy, where they appeared.
Especially often such lights were observed on the masts of ships. The Roman philosopher and writer Lucius Seneca said that during a thunderstorm, "the stars seem to descend from the sky and sit on the masts of ships." Among the many stories about this, the testimony of the captain of an English sailing ship is interesting.
It happened in 1695, in the Mediterranean Sea, near the Balearic Islands, during a thunderstorm. Fearing a storm, the captain ordered the sails to be lowered. And then the sailors saw more than thirty Elm's lights in different places on the ship. On the weather vane of a large mast, the fire reached more than half a meter in height. The captain sent a sailor with orders to take him down. Rising upstairs, he shouted that the fire hissed like a rocket from wet powder. He was ordered to remove it along with the weather vane and bring it down. But as soon as the sailor removed the weather vane, the fire jumped to the end of the mast, from where it was impossible to remove it.
An even more impressive picture was seen in 1902 by the sailors of the Moravia steamer. While off the Cape Verde Islands, Captain Simpson wrote in the ship's log: “Lightning blazed in the sea for an hour. The steel ropes, the tops of the masts, the knuckles, the knuckles of the cargo booms - everything shone. It seemed that lighted lamps were hung on the quarter quarters every four feet, and bright lights shone at the ends of the masts and nocrays. The glow was accompanied by an unusual noise:
“It was as if myriads of cicadas settled in a rig, or deadwood and dry grass burned with a crackle ...”
The fires of St. Elmo are varied. They come in the form of a uniform glow, in the form of separate flickering lights, torches. Sometimes they are so similar to flames that they rush to extinguish them.
The American meteorologist Humphrey, who observed the Elmo fires on his ranch, testifies: this natural phenomenon, "turning every bull into a monster with fiery horns, gives the impression of something supernatural." This is said by a person who, by his very position, is not capable, it would seem, of being surprised at such things, but must accept them without unnecessary emotions, relying only on common sense.
It can be safely asserted that even today, despite the dominance - far, though not universal - of the natural-scientific worldview, there will be people who, if they were in the position of Humphrey, would see something beyond reason in the fiery bull horns. There is nothing to say about the Middle Ages: then, most likely, the machinations of Satan would be seen in the same horns.
Corona discharge, electric corona, a type of glow discharge that occurs when a sharply pronounced inhomogeneity of the electric field near one or both electrodes. Similar fields are formed at electrodes with a very large curvature of the surface (points, thin wires). During a corona discharge, these electrodes are surrounded by a characteristic glow, also called a corona, or corona layer.
The non-luminous (“dark”) region of the interelectrode space adjacent to the corona is called the outer zone. Corona often appears on tall, pointed objects (St. Elmo's lights), around power lines, etc. Corona discharge can occur at various gas pressures in the discharge gap, but it manifests itself most clearly at pressures not lower than atmospheric.
The appearance of a corona discharge is explained by an ion avalanche. There are always a certain number of ions and electrons in a gas, arising from random causes. However, their number is so small that the gas practically does not conduct electricity.
At a sufficiently high field strength, the kinetic energy accumulated by the ion in the interval between two collisions can become sufficient to ionize a neutral molecule during the collision. As a result, a new negative electron and a positively charged residue, an ion, are formed.
When a free electron collides with a neutral molecule, it splits it into an electron and a free positive ion. Electrons, upon further collision with neutral molecules, again split them into electrons and free positive ions, and so on.
Such an ionization process is called impact ionization, and the work that needs to be expended to produce an electron detachment from an atom is called ionization work. The work of ionization depends on the structure of the atom and is therefore different for different gases.
The electrons and ions formed under the influence of impact ionization increase the number of charges in the gas, and in turn they are set in motion under the action of an electric field and can produce impact ionization of new atoms. Thus, the process amplifies itself, and the ionization in the gas quickly reaches a very high value. The phenomenon is similar to an avalanche, so this process was called an ion avalanche.
Let us stretch on two high insulating supports a metal wire ab, having a diameter of several tenths of a millimeter, and connect it to the negative pole of a generator, which gives a voltage of several thousand volts. We will take the second pole of the generator to the Earth. You get a kind of capacitor, the plates of which are the wire and the walls of the room, which, of course, communicate with the Earth.
The field in this capacitor is very non-uniform, and its intensity near a thin wire is very high. By gradually increasing the voltage and observing the wire in the dark, one can notice that at a known voltage, a weak glow (crown) appears near the wire, covering the wire from all sides; it is accompanied by a hissing sound and a slight crackle.
If a sensitive galvanometer is connected between the wire and the source, then with the appearance of a glow, the galvanometer shows a noticeable current flowing from the generator through the wires to the wire and from it through the air of the room to the walls, between the wire and the walls is transferred by ions formed in the room due to impact ionization.
Thus, the glow of the air and the appearance of a current indicate a strong ionization of the air under the action of an electric field. Corona discharge can occur not only near the wire, but also near the tip and in general near any electrodes, near which a very strong inhomogeneous field is formed.
Application of corona discharge
Electric cleaning of gases (electrostatic precipitators). A vessel filled with smoke suddenly becomes completely transparent if sharp metal electrodes connected to an electrical machine are introduced into it, and all solid and liquid particles will be deposited on the electrodes. The explanation of the experience is as follows: as soon as the corona is ignited, the air inside the tube is strongly ionized. Gas ions stick to dust particles and charge them. Since a strong electric field acts inside the tube, the charged dust particles move under the action of the field to the electrodes, where they settle.
Elementary particle counters
The Geiger-Muller elementary particle counter consists of a small metal cylinder equipped with a window covered with foil and a thin metal wire stretched along the axis of the cylinder and insulated from it. The counter is connected to a circuit containing a current source, the voltage of which is equal to several thousand volts. The voltage is chosen necessary for the appearance of a corona discharge inside the counter.
When a fast moving electron enters the counter, the latter ionizes the gas molecules inside the counter, causing the voltage required to ignite the corona to decrease somewhat. A discharge occurs in the counter, and a weak short-term current appears in the circuit. To detect it, a very large resistance (several megaohms) is introduced into the circuit and a sensitive electrometer is connected in parallel with it. Each time a fast electron hits the inside of the counter, the sheets of the electrometer will bow.
Such counters make it possible to register not only fast electrons, but in general any charged, rapidly moving particles capable of producing ionization by means of collisions. Modern counters can easily detect even a single particle hitting them and therefore make it possible to verify with complete certainty and very great clarity that elementary charged particles really exist in nature.
lightning rod
It is estimated that about 1800 thunderstorms occur simultaneously in the atmosphere of the entire globe, which give an average of about 100 lightning per second. And although the probability of being struck by lightning of any individual person is negligible, nevertheless, lightning causes a lot of harm. Suffice it to point out that at present about half of all accidents in large power lines are caused by lightning. Therefore, lightning protection is an important task.
Lomonosov and Franklin not only explained the electrical nature of lightning, but also pointed out how to build a lightning rod that protects against a lightning strike. The lightning rod is a long wire, the upper end of which is sharpened and strengthened above the highest point of the protected building. The lower end of the wire is connected to a metal sheet, and the sheet is buried in the ground at the level of soil water.
During a thunderstorm, large induced charges appear on the Earth and a large electric field appears near the Earth's surface. Its intensity is very high near sharp conductors, and therefore a corona discharge is ignited at the end of the lightning rod. As a result, induced charges cannot accumulate on the building and lightning does not occur. In those cases when lightning still occurs (and such cases are very rare), it strikes the lightning rod and the charges go to the Earth without harming the building.
In some cases, the corona discharge from the lightning rod is so strong that a clearly visible glow appears at the tip. Such a glow sometimes appears near other pointed objects, for example, at the ends of ship masts, sharp treetops, etc. This phenomenon was noticed several centuries ago and caused the superstitious horror of navigators who did not understand its true essence.
corona discharge electric corona, a kind of glow discharge (See glow discharge) ;
occurs with a pronounced inhomogeneity of the electric field near one or both electrodes. Similar fields are formed at electrodes with a very large curvature of the surface (points, thin wires). At K. r. these electrodes are surrounded by a characteristic glow, also called the corona, or corona layer. The non-luminous (“dark”) region of the interelectrode space adjacent to the corona is called the outer zone. The crown often appears on tall pointed objects (St. Elmo's lights), around power line wires, etc. K. r. can take place at various gas pressures in the discharge gap, but it manifests itself most clearly at pressures not lower than atmospheric pressure. The discharge starts when the voltage U between the electrodes reaches the so-called "initial potential" of the corona U 0(typical values are thousands and tens of thousands in). Current K. r. proportional to the difference U-U 0 and the mobility of the gas ions formed in the discharge (see Mobility of ions and electrons); it is usually small (fractions ma for 1 cm corona electrode length). With an increase U the brightness and thickness of the corona layers increase. When U reaches the potential of "spark overlap", K. r. goes into Spark Discharge.
If only the anode coronas, the corona is called positive. In this case, primary electrons are released at the outer boundary of the corona layer as a result of photoionization of the gas (see Ionization) by photons emitted inside the corona. Accelerating in the anode field, these electrons impactly excite atoms and ions of the gas and in the acts of impact ionization generate electron avalanches. In the outer zone, current carriers are positive ions; the positive space charge formed by them limits the current K. r. In the negative corona, positive ions, accelerated by a strong field near the corona cathode, knock out electrons from it (secondary electron emission). Having flown out of the cathode, the electrons shock ionize the gas, generating avalanches and ensuring the reproduction of positive ions. In pure electropositive gases, the current in the outer zone is carried by electrons, and in the presence of electronegative gases that have electron affinity (See Electron affinity) , -
negative ions arising from the "sticking together" of electrons and neutral gas molecules (see Electronegativity). These electrons or ions form a negative space charge in the outer zone, which limits the current of the K. r. In a bipolar corona, both electrodes corona. The processes in corona layers are similar to those described; in the outer zone, the current is carried by counter flows of positive ions and electrons (or negative ions). With a periodic change in the polarity of the electrodes (AC r.), the low-mobility heavy ions in the outer zone do not have time to reach the electrodes during one half-cycle, and oscillations of the space charge occur. K. r. at frequencies of the order of 100,000 Hz and above is called a high-frequency corona (See High-frequency corona).
In K. r. electrical energy is converted mainly into thermal energy - in collisions, ions give off the energy of their movement to neutral gas molecules. This mechanism causes significant energy losses on high voltage transmission lines. Useful application To. found in electrical separation processes (See Electrical Separation) (e.g. in electrical filters (See Electrical Filter)) ,
electric painting (in particular, for applying powder coatings), as well as when registering ionizing radiation (Geiger-Muller counter ami). Lit.: Kaptsov N. A., Corona discharge and its application in electrostatic precipitators, M., 1947; Leb L., Basic processes of electrical discharges in gases, trans. from English, M.-L., 1950; Granovsky VL Electric current in gas. Unsteady current, M., [in print]. A. K. Musin.
Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what "Corona Discharge" is in other dictionaries:
High-voltage independent. electric discharge in a gas at a pressure of p? 1 atm, arising in a sharply inhomogeneous electric. field near electrodes with a large curvature of the surface (points, wires). In these zones, ionization and excitation of neutrons occur ... Physical Encyclopedia
An electric discharge in a gas that usually occurs at a pressure not lower than atmospheric if the electric field between the electrodes (in the form of points, thin wires) is not uniform. Ionization and glow of gas in a corona discharge occur only in ... ... Big Encyclopedic Dictionary
corona discharge- corona discharge; corona A discharge in which a strongly inhomogeneous electric field is additionally significantly distorted by the space charges of ions near the electrodes, where ionization and excitation (glow) of a gas or liquid occurs ... Polytechnic terminological explanatory dictionary
corona discharge- A more or less constant luminous electrical discharge in the atmosphere, emanating from objects towering above the ground or from flying aircraft, sometimes accompanied by a crack. Syn.: Saint Elmo's fire... Geography Dictionary
corona discharge- crown - [Ya.N. Luginsky, M.S. Fezi Zhilinskaya, Yu.S. Kabirov. English-Russian Dictionary of Electrical Engineering and Power Industry, Moscow, 1999] Electrical engineering topics, basic concepts Synonyms corona EN coronacorona discharge ... Technical Translator's Handbook
This term has other meanings, see Discharge ... Wikipedia
An electric discharge in a gas that usually occurs at a pressure not lower than atmospheric if the electric field between the electrodes (in the form of sharp, thin wires) is not uniform. Ionization and glow of gas in a corona discharge occur only in ... ... encyclopedic Dictionary
Corona, an electric discharge in a gas that usually occurs at a pressure not lower than atmospheric pressure, if the electric field near one or both electrodes is sharply inhomogeneous. Similar fields are formed at electrodes with a very large curvature of the surface ... ... Encyclopedia of technology
corona discharge- vainikinis išlydis statusas T sritis fizika atitikmenys: angl. corona discharge vok. Koronaentladung, f rus. corona discharge, m pranc. décharge en couronne, f … Fizikos terminų žodynas
Crown (from lat. corona crown, wreath), an electric discharge in a gas that usually occurs at a pressure not lower than atmospheric, if the electric. the field between the electrodes (in the form of points, thin wires) is non-uniform. It manifests itself in the form of a glow of ionizers. ... ... Big encyclopedic polytechnic dictionary
corona discharge - this is a phenomenon associated with the ionization of air in an electric field with a high intensity (glow of gases in a non-uniform electric field of high intensity).
Areas with high intensity are often formed due to the inhomogeneity of the electric field that occurs:
1) When choosing the wrong parameters during the design process;
2) As a result of pollution arising in the course of work;
3) As a result of mechanical damage and equipment wear.
Similar fields are formed at electrodes with a very large curvature of the surface (points, thin wires). When the field strength reaches the limit value for air (about 30 kV / cm), a glow appears around the electrode, which has the form of a shell or crown (hence the name). Corona discharge is used to clean gases from dust and other contaminants (electrostatic precipitator), to diagnose the state of structures (allows you to detect cracks in products). On power lines, the occurrence of a corona discharge is undesirable, as it causes significant losses in the transmitted energy. In order to reduce the relative curvature of the electrodes, multi-wire lines (3, 5 or more wires in a certain way) are used.
Types of crowns and their identification
Negative "flame-like" corona. This type of corona usually occurs on a negatively charged conductor, such as during the negative half-wave of mains voltage. This type of crown looks like a flame, the shape, direction and size of which is constantly changing. This corona is very sensitive to changes in environmental parameters. Its occurrence also leads to the appearance of an audio signal approximately twice the industrial frequency (for example, 100 Hz) or a multiple of it.
breakdowns
Breakdowns usually form between two insulated but closely spaced metal plates. The leakage current along the support induces certain levels of voltage between the plates and thus a discharge between them. These discharges are usually difficult to localize, since there is no direct connection to the high voltage line. In a CoroCAM camera, these spark gaps will appear as small, permanent, and very bright objects. The sound produced by these discharges has a higher pitch than negative coronas and seems unrelated to power frequency. Spark gaps usually cause large radio and television interference (eg high RI - radio interference).
Positive glow corona
A positive glow corona discharge is formed on a positively charged conductor (for example, during a positive half-wave of the mains voltage). It is usually found in places with sharp corners. This type of crown is small in size and looks like a glow around a certain place. This is a relatively weak corona source and produces a very small audio signal.
How serious is corona/discharge in terms of radio interference voltage (RIV)?
General remarks:
All spark gaps cause serious radio interference.
If the corona is completely visible to the naked eye (at night), then it will cause serious radio interference. (Use the CoroCAM camera to quickly locate all sources of corona and then try to see them with the naked eye.)
Positive glow corona does not cause serious radio interference.
Application of corona discharge
Electric cleaning of gases (electrostatic precipitators).
A vessel filled with smoke suddenly becomes completely transparent if sharp metal electrodes connected to an electrical machine are introduced into it, and all solid and liquid particles will be deposited on the electrodes. The explanation of the experience is as follows: as soon as the corona is ignited, the air inside the tube is strongly ionized. Gas ions stick to dust particles and charge them. Since a strong electric field acts inside the tube, the charged dust particles move under the action of the field to the electrodes, where they settle.
Counters of elementary particles.
The Geiger-Muller elementary particle counter consists of a small metal cylinder equipped with a window covered with foil and a thin metal wire stretched along the axis of the cylinder and insulated from it. The counter is connected to a circuit containing a current source, the voltage of which is equal to several thousand volts. The voltage is chosen necessary for the appearance of a corona discharge inside the counter.
When a fast moving electron enters the counter, the latter ionizes the gas molecules inside the counter, causing the voltage required to ignite the corona to decrease somewhat. A discharge occurs in the counter, and a weak short-term current appears in the circuit. To detect it, a very large resistance (several megaohms) is introduced into the circuit and a sensitive electrometer is connected in parallel with it. Each time a fast electron hits the inside of the counter, the sheets of the electrometer will bow.
Such counters make it possible to register not only fast electrons, but in general any charged, rapidly moving particles capable of producing ionization by means of collisions. Modern counters can easily detect even a single particle hitting them and therefore make it possible to verify with complete certainty and very great clarity that elementary charged particles really exist in nature.
lightning rod
It is estimated that about 1800 thunderstorms occur simultaneously in the atmosphere of the entire globe, which give an average of about 100 lightning per second. And although the probability of being struck by lightning of any individual person is negligible, nevertheless, lightning causes a lot of harm. Suffice it to point out that at present about half of all accidents in large power lines are caused by lightning. Therefore, lightning protection is an important task.
Lomonosov and Franklin not only explained the electrical nature of lightning, but also pointed out how to build a lightning rod that protects against a lightning strike. The lightning rod is a long wire, the upper end of which is sharpened and strengthened above the highest point of the protected building. The lower end of the wire is connected to a metal sheet, and the sheet is buried in the ground at the level of soil water. During a thunderstorm, large induced charges appear on the Earth and a large electric field appears near the Earth's surface. Its intensity is very high near sharp conductors, and therefore a corona discharge is ignited at the end of the lightning rod. As a result, induced charges cannot accumulate on the building and lightning does not occur. In those cases when lightning still occurs (and such cases are very rare), it strikes the lightning rod and the charges go to the Earth without harming the building.
In some cases, the corona discharge from the lightning rod is so strong that a clearly visible glow appears at the tip. Such a glow sometimes appears near other pointed objects, for example, at the ends of ship masts, sharp treetops, etc. This phenomenon was noticed several centuries ago and caused the superstitious horror of navigators who did not understand its true essence.
Under the influence of a corona discharge
Electrostatic precipitators are the most efficient gas cleaning devices, because. operating costs for their maintenance, in comparison with other dust and ash collectors, are much lower. At the same time, electrostatic precipitators most fully meet the requirements of an absolute dust-collecting device.
The installation for electric gas cleaning includes an electrostatic precipitator and a power unit. The gas to be purified enters the electrostatic precipitator, the electrodes of which are supplied with a high voltage, a corona discharge occurs between the electrodes, as a result of which the interelectrode space is filled with negatively charged gas ions, which, under the influence of an electric field, move from the corona electrodes to the precipitation ones.
Collecting electrodes are divided into plate, tubular, box-shaped, rod, pocket, grooved, C-shaped, tulip-shaped, etc.
According to the method of removing dust, electrostatic precipitators are divided into wet and dry. In dry electrostatic precipitators, shaking of the electrodes is carried out by shock-hammer, shock-pulse, vibration methods, etc. In wet electrostatic precipitators, periodic or continuous washing of the electrodes is carried out. In the direction of movement of the purified gas, electrostatic precipitators are divided into vertical and horizontal. In addition, electrostatic precipitators are single-zone, in which the charging and deposition of particles is carried out in one zone, and two-zone, in which charging and deposition are carried out in different zones: the ionizer and the precipitator.
Tubular electrostatic precipitator Sturtevant
According to the principle of creating a corona discharge, electrostatic precipitators come with fixed points of a corona discharge and a non-fixed corona discharge.
According to the type of corona electrode systems, electrostatic precipitators can be divided into two main groups: with frame corona electrodes and with freely suspended corona electrodes. The shaking of the precipitation and corona electrodes is carried out with the help of impact, shock-hammer shaking, shock-pulse system, vibration mechanisms, periodic and continuous washing.
The physics of a corona discharge is considered in detail in the book by N.A. Kaptsov “Corona discharge and its application in electrostatic precipitators”, published in 1947. The phenomenon of an electric discharge in gases is explained by several discharge theories. The basis of the first theory - the theory of avalanches - was laid by Townsend in 1900. Thirty years later, it was further developed in the works of Rogovsky and, as N.A. Kaptsov writes, "and has until now served as the basis for explaining the phenomena of a corona discharge." The second theory - the theory of gas-discharge plasma - has been developed since 1924 by Lengryum and his school, but, according to N.A. Kaptsov, it has no direct relation to the explanation of the physics of a corona discharge. The third theory - the theory of isothermal plasma - was developed in the pre-war years by Elenbas and other Dutch physicists.
Corona discharge is an independent discharge that occurs only under the condition of a very large inhomogeneity of the electric field at least at one of the electrodes (a point is a plane, a thread is a plane, two threads, a thread in a cylinder of large radius, etc.). The conditions for the emergence and development of the corona are different for different polarities of the "tip" (let's call it the electrode, near which E highly heterogeneous).
If the tip is a cathode (the corona is “negative”), then the corona is ignited essentially in the same way as in a glow discharge, only to determine the first Townsend coefficient (since the field E strongly inhomogeneous) in air (a practically important case), sticking (presence of oxygen) must be taken into account, so that
((x)- p ( x))dx=ln(l+ -1), (8.26)
where p - application coefficient, x 1 - distance to the point where E already so small that ionization does not occur: E 0. In such a corona there is a glow only up to a distance, also approximately equal to x one . If the “tip” is an anode (the corona is “positive”), then the picture changes significantly: near the tip, luminous filaments are observed, as if running away from the tip (Fig. 8.9). Probably, these are streamers from avalanches generated in the volume by photoelectrons. It is obvious that the ignition criterion is also different - the same as for the formation of a streamer. In any corona discharge, the inhomogeneity is significant E, those. specific electrode geometry.
There is no complete clarity in the discharge combustion mechanism, but this does not prevent the use of corona discharges in industry (electrostatic precipitators); Corona discharge also works in Geiger-Muller counters. But it can also be harmful, for example, on high-voltage lines (LEP), corona discharges create noticeable losses.
Coronas are intermittent with different frequencies: for positive ones up to 10 4 Hz, for negative ones - 10 6 Hz - and this is the interference radio range. The mechanism of discontinuous discharge near the positive corona is apparently related to the fact that the streamer electrons are drawn into the anode, the positive cores shield the anode, and new streamers cannot be created until the cores go to the cathode. Then the anode will "open" and the pattern will repeat itself. For a negative corona, the presence of oxygen in the air is essential - moving a little away from the corona, electrons stick to oxygen, negative ions shield the tip, and until they go to the anode, the discharge stops. After the departure of the ions, the discharge will reappear and the picture will be repeated.
Rice. 8.9. Streamer from a positive rod with a diameter of 2 cm to a plane at a distance of 150 cm at a constant voltage of 125 kW; on the right - the calculation, the equipotential surfaces are drawn, the numbers near the curves are the fractions of the applied voltage, counted from the plane; on the left - a photo of streamers in the same conditions
High frequency (HF) discharges
In the HF range (10 -1 10 2 MHz), it is customary to distinguish E and H types of discharges - according to the defining vector of the electromagnetic field. In laser technology, they use E(capacitive) discharges, placing the working volume in a capacitor, to the plates of which an RF voltage is applied (the plates are sometimes directly injected into the volume, sometimes they are insulated with a dielectric - usually glass). The power of these discharges is small (their task is to support ionization), but the intensity E large - up to tens of keV.
Application of HF induction fields (H-fields) has become very wide since the end of the 40s, although mainly in the form of HF furnaces. Wherever pure heat is needed and there is a conductive medium, H fields are irreplaceable. This includes the production of semiconductor materials, and zone melting of pure metals, and ultra-pure chemical compounds, and even household furnaces.
Rice. 8.10. Induction discharge in a tube with a radius R, inserted into a long solenoid; r 0 - plasma radius, on the right - temperature distribution along the radius
True, in these devices there is almost no need to match the generator and the load - the ratio of the reactive and active resistances of the load changes little. But in discharges, the matter is more complicated: changes in the parameters of the discharge medium (resistance, self-induction, mutual induction - connection with the inductor) can vary over a wide range. Usually an inductor is a coil (there is even one turn!), inside which a discharge occurs (Fig. 8.10).
The alternating field is directed along the coil axis, the field is axial to it. To maintain the discharge, the required is significantly less than to ignite it. Therefore, a thin metal electrode is usually introduced into the volume, it heats up, gives off thermoelectrons (sometimes partially evaporates), initiates a discharge, after which it is removed. During operation, power is introduced by the flow of electromagnetic energy:
< S> = (s/4 )<ЕН >, (8.27)
and is removed most often by a gas flow (it is ionized and carries away energy). But electromagnetic energy penetrates into the plasma (conductor) to a depth X, decreasing exponentially exp(-x/), where is the so-called skin layer, and it was agreed to consider it as the depth of penetration of the flow:
2 = c 2 /(2) , (8.28)
where c is the speed of light, is the conductivity of the conductor, is the RF frequency
If < R, then the energy is absorbed, in a layer of thickness δ, forming a conducting cylinder. Temperature radius distribution T and conductivity σ are shown in Figs. 8.11, in essence, this is a complete analogue of the channel model of the arc, it is called the "metal cylinder model". It should be noted that it is actually possible to control the pressure R(preferably more!) and flow<ЕН>, determined by ampere-winds:
<ЕН> ~ IN(where I- current, N- number of turns per unit length of the inductor).
CORONA DISCHARGE, one of the types of electric discharge in a gas that occurs in a sharply inhomogeneous electric field at an electrode with a small radius of curvature (points, thin wires). The most famous corona discharge in air, accompanied by a glow and a characteristic crackle.
or simply a corona, arises as a result of the processes of ionization of atoms and molecules of gas in a region of high electric field strength at a small electrode and is limited to this region. Ionization leads to the appearance of charged gas particles: free electrons and positive ions, and in electronegative gases, which include air, to the appearance of negative ions. When electrons move in an electric field, they acquire energy sufficient for the subsequent ionization of atoms and molecules, there is a sharp increase in the number of charged particles, which leads to the formation of an electron avalanche and the appearance of a corona discharge. Depending on the polarity of the electrode and the magnitude of the acting voltage, the corona discharge can have an avalanche or streamer form. With a negative polarity of the electrode and not too high voltages, an avalanche corona discharge usually occurs, characterized by a uniform glow of gas (for example, air) at the tip of the electrode. With the positive polarity of the small electrode outside the narrow ionization zone, the current is carried to the other electrode or to the ground by a stream of positive ions. A streamer corona discharge occurs most often at the positive electrode at an increased electric field strength and consists of ionized branching channels extending from the electrode (see Streamers). Outwardly, it resembles a luminous crown (drawing), which gave the name to this form of electric discharge.
Depending on the type of applied voltage, a pulsed corona discharge is distinguished, which is most often a streamer discharge, an alternating current corona discharge that occurs in each half-cycle of the applied voltage, and a DC corona discharge, the shape of which significantly depends on the polarity of the electrode and can be intermittent.
Charged particles (electrons and ions) formed in the corona, when they move in an electric field, receive energy from it, which leads to energy loss during a corona discharge. This is especially evident during a corona discharge on the wires of power lines (TL). The corona discharge on the wires of power lines is accompanied by hissing and crackling, and in the dark and in the rain - a glow. In addition, corona discharge creates radio interference. But the corona discharge can also be a useful source of charged particles, in particular, when it is used in electrostatic precipitators.
Lit.: Kaptsov N.A. Corona discharge and its application in electrostatic precipitators. M.; L., 1947; Levitov V. I. Crown of alternating current. 2nd ed. M., 1969; Raizer Yu. P. Physics of gas discharge. 2nd ed. M., 1992; Sokolova M. V. Corona discharge in gases // Encyclopedia of Low-Temperature Plasma / Edited by V. E. Fortov. M., 2000. T. 2.