Plasma, properties, types, preparation and use

Plasma, properties, types, production and application.



Plasma is the fourth state of matter, formed very hot ionized gas consisting of electrons and ions.


Plasma, definition, concept, features

The most typical form of plasma. The types of plasma. Classification of plasma

Properties of plasma. Conditions – criteria for the recognition of a plasma system with charged particles. The plasma parameters

The difference between plasma from the gas

Receiving (establishment) and application of plasma


Plasma, definition, concept, features:

Plasma (from Greek. πλάσμα “fashioned”, “decorated”) is the fourth state of matter, formed very hot ionized gas consisting of electrons and ions. Its composition may include not only ions and electrons but also atoms, molecules, and any other charged particles with positive and negative charges (e.g., quark-gluon plasma). Moreover, the number of positively and negatively charged particles is about the same. They move simultaneously rather than in pairs, as in classical gas, substantially increasing the conductivity of the substance and its dependence on electromagnetic fields. In itself the plasma is quasi-neutral – the amount of charge it any amount as close as possible to zero.

Plasmathat contains electrons and positive ions, called electron-ion plasma. If the plasma near the charged particles are neutral molecules, it is called partially ionized. Plasmathat consists of charged particles, is called completely ionized.

For the system with charged particles become a plasma, they have to be located at a minimum distance from each other and interact. When such effects become collective and a lot of them, there comes the desired state. For him (such a state) characteristic temperature 8000 degrees Kelvin. Due to the constant motion of particles of plasma is a good conductor of electric current. And using the magnetic field to concentrate it in the jet and to control further movement.

In terrestrial conditions, the plasma state of matter is quite rare and unusual. But across the Universe, plasma is the most common state of matter. It consists of the Sun, the stars, the upper atmosphere and radiation belts of the Earth. The Northern lights are also the result of processes occurring in the plasma.


The most typical form of plasma:

The most typical forms of plasma are presented in the table below:

Artificially created plasma: Earth’s natural plasma:


Space and astrophysical plasmas:


– plasma screen (TV, monitor)

the substance inside of fluorescent (including compact) and neon lamps

– plasma rocket engines,

– corona discharge ozone generator,

– controlled thermonuclear fusion,

– an electric arc in the arc lamp in arc welding,

plasma lamp,

arc discharge from a Tesla coil,

– the impact on the substance by laser radiation

A bright sphere of a nuclear explosion

– lightning

– St. Elmo’s fire,

– ionosphere,

a flame (low temperature plasma)

the sun and other stars (those that exist due to thermonuclear reactions),

the solar wind,

– space (space between planets, stars and galaxies),

– interstellar nebula


The types of plasma. Classification of plasma:

Plasma may be:

– artificial and natural.

Examples of natural plasma: a planetary nebula, interplanetary plasma, the Earth’s ionosphere, the solar chromosphere of the Sun and stars, solar prominence, solar spicules, solar wind, solar corona, the photosphere of the Sun and stars, chromosphere flash, lightning.

high temperature (temperature of million degrees Kelvin and above) and low-temperature (temperature less than a million degrees Kelvin).

From low-temperature plasma , the average electron energy is less than the characteristic ionization potential of the atom (<10 eV). It (low temperature plasma), as a rule, is a partially ionized gas, i.e., the number of neutral atoms and molecules greatly exceeds the number of charged particles – electrons and ions. For low temperature plasmas characteristic of the low degree of ionization is about 1 %.

If the low-temperature plasma contains many macroscopic solid particles (the size from fractions to hundreds of micrometers) with high electric charge are either spontaneously formed in the plasma as a result of various processes, either introduced into the plasma from the outside, it is called a dusty plasma. Dusty plasma is a special case of low-temperature plasma.

Low-temperature plasma, called plasma technologyas it is introduced into the process. Be plasma etched and modify the properties of surfaces (creating a diamond film, nitriderm metals, changing the wettability), clean gases and liquids.

Low-temperature plasma in accordance with the physical properties can be stationary or non-stationary, quasi-stationary, equilibrium, nonequilibrium, perfect, imperfect.

Examples of low-temperature plasma and its sources: flames, sparks, various types of lasers, cathode blast, cathode spot, cathode torch, plasma torch, plasma burner, a photoresonant plasma produced thermionic Converter, the MHD generator.

High-temperature plasma is also called hot plasma. Hot plasma is almost always completely ionized (degree of ionization ~100 %).

Substance in a state of high-temperature plasma has high ionization and electrical conductivity, which allows its use in controlled thermonuclear synthesis.

fully ionized and partially ionized.

The ratio of the number of ionized atoms to the total number per unit volume is called the degree of ionization of the plasma. The degree of ionization of the plasma to a large extent determines its properties, including electrical and electromagnetic.

The degree of ionization is determined by the following formula:

α = ni / (ni + na),

where α is the degree of ionization, ni – ion concentration and na is the concentration of neutral atoms.

It is obvious that the maximum value of α equal to 1 (or 100 %). The plasma with the ionization degree 1 (or 100 %) is called a fully ionized plasma.

Substance with a degree of ionization less than 1 (or less than 100 %), is called partially ionized plasma;

– perfect and imperfect. These types are characteristic only for low-temperature plasma.

When a conditional field is going possible maximum of interacting particles, the plasma becomes ideal. If dissipative processes are present, the ideality is violated.

So, if in the sphere of the Debye radius (rD) is a lot of charged particles and for her the condition N ≈ 4π·n·r3D / 3 ≫1 the plasma is called ideal plasma

where rD is the Debye radius, n is the concentration of all the particles in the plasma, N is the ideality parameter.

For N, we 1 for a nonideal plasma.

In ideal plasmas the potential energy of interaction between particles is small compared to their thermal energy;

equilibrium and nonequilibrium. These types are characteristic only for low-temperature plasma.

The equilibrium plasma is called low-temperature plasma, if its components are in a state of thermodynamic equilibrium, i.e. the temperature of electrons, ions and neutral particles is the same. Equilibrium plasma typically has a temperature of more than several thousand degrees Kelvin.

Examples of equilibrium plasmas can be the Earth’s ionosphere, flame, carbon arc, plasma torch, lightning, optical discharge, the surface of the Sun, an MHDgenerator, thermionic Converter.

In non-equilibrium plasma , the electron temperature greatly exceeds the temperature of other components. This is due to the differences in the masses of neutral particles, ions and electrons, which complicates the process of exchange of energy.

Plasma substance created by artificial means, initially you do not have thermodynamic equilibrium. Equilibrium appears only when a significant heating of the substance, and thus increase the number of random collisions of particles with each other, which is possible only if the decrease in portable them the energy;

stationary, non-stationary and quasi-stationary. These types are characteristic only for low-temperature plasma.

Stationary low-temperature plasma has a large lifetime compared to the times of relaxation at her. Non-stationary (pulsed) low-temperature plasma lives for a limited time, defined as the time of establishing the equilibrium in the plasma and the external environment. Low-temperature plasma, the lifetime of which exceeds the characteristic time of transient processes, called quasi-stationary plasma. An example of a quasi-stationary plasma is a discharge plasma;

classical and degenerate. Classical plasma, called a, where the distance between particles is much greater than the length of de Broglie. In such a plasma the particles can be considered as point charges.

Degenerate plasma – a plasma in which comparable length the de-Broglie wavelength with the distance between the particles. In such a plasma it is necessary to consider quantum effects of interaction between particles.

one-component and multi-component (depending on fill it ion);

the quark-gluon. The quark-gluon plasma – androna environment with mixed color charges (quarks and gluons antiquarii), formed when the face of heavy ultra-relativistic particles in the medium with high energy density;

cryogenic. Cryogenic plasma is plasma is cooled to low (cryogenic) temperatures. For example, by immersion in a bath of liquid nitrogen or helium;

gas discharge. Discharge plasma – the plasma created in the gas discharge;

– plasma Plasma solids. solids form the electron and hole semiconductors in the compensation of their charges ions in the crystal lattices;

– laser. Laser plasma arises from the optical breakdown generated by high power laser radiation upon irradiation of a substance.

There are other subtypes of plasma substance.


Properties of plasma:

The main property of plasma substance is in its high electrical conductivitysubstantially exceeding that observed in other aggregate States.

The plasma affects the electromagnetic field, in order to form the desired shape, number of layers and density. Charged particles move along and across the direction of the electromagnetic field, their motion is translational or rotational. This property of plasma is also called the interaction of the plasma with the external electromagnetic field or electromagnetic property of plasma.

Plasma glows, has zero total charge and a high frequency, leading to vibration.

Despite the high electrical conductivity of it (the plasma) quasi-neutral particles with positive and negative charges are almost equal to the bulk density.

To save the properties of the plasma, it should not contact a cold and dense environment.

For particles of the plasma is characterized by the so-called collective interaction. It means that charged particles of the plasma due to the presence of electromagnetic charge, they interact simultaneously with a system of closely spaced charged particles and not in pairs as regular gas.


Conditions – criteria for the recognition of a plasma system with charged particles:

Any system with charged particles corresponds to the definition of plasma in the presence of the following conditions are met:

of sufficient density fills its electrons, ions and other structural units of the substance to each of them interacted with the whole system of closely spaced charged particles. Collective interaction of charged particles and their location must be as close as possible and stay in the sphere of influence (sphere of radius Debye).

The condition is met when the number of charged particles in a sphere of influence (sphere of radius Debye) sufficient for the occurrence of collective effects.

Mathematically this condition can be expressed as:

r3D·N ≫ 1, where r3D is the sphere of the Debye radius, N is the concentration of charged particles;

priority internal interactions. This means that the radius of babaevskogo shielding must be small compared to the characteristic size of the plasma. The condition is satisfied, when the surface effects compared to the significant internal effects of the plasma becomes negligible and neglected.

Mathematically this condition can be expressed as:

rD / L ≪ 1, where rD is the Debye radius, L – the characteristic size of a plasma;

the appearance of the plasma frequency. This criterion means that the average time between particle collisions is large compared with the period of plasma oscillations. The condition is satisfied upon the occurrence of plasma oscillations beyond the molecular-kinetic.


The plasma parameters:

The fourth state of matter there are the following options:

the concentration of its constituent particles.

In the plasma of all its components randomly. To measure their concentration per unit volume, first divide the contained particle populations (electrons, ions, other neutral), then sorts the ions themselves, and find the values for each species separately (ne, ni and na), where ne is the concentration of free electrons, ni is the concentration of ions, na is the concentration of neutral atoms;

the degree and the multiplicity of ionization.

In order to turn the substance into the plasma it is necessary to ionize. The degree of ionization is proportional to the number of atoms, given or absorbed electrons, and depends on temperature. The ratio of the number of ionized atoms to the total number per unit volume is called the degree of ionization of the plasma. The degree of ionization of the plasma to a large extent determines its properties, including electrical and electromagnetic.

The degree of ionization is determined by the following formula:

α = ni / (ni + na),

where α is the degree of ionization, ni – ion concentration and na is the concentration of neutral atoms.

α is a dimensionless parameter that indicates how many atoms of a substance able to give or absorb electrons. It is clear that Amax = 1 (100%), and the average charge of the ions, also called the multiplicity of ionization (Z) will be in the range of ne = <Z> ni where ne is the concentration of free electrons.

When Amax plasma is fully ionized, which is typical mainly for the “hot” substance – high-temperature plasma.

the temperature. Different substances present in the plasma at different temperatures, due to the structure of external electronic shells of atoms: the lighter the atom gives an electron, the lower the transition temperature in the plasma state.


The difference between plasma and gas:

Plasma – a kind of derivative of gas, resulting in ionization. However, they have certain differences.

First of all, it is the presence of electrical conductivity. Conventional gas (e.g. air) it tends to zero. Most gases are good insulators, not yet thrown an additional impact. Plasma is an excellent conductor.

Due to the extremely small electric field plasma substance-dependent magnetic fields, which is not typical for gases. This leads to filamentary and stratification. And the predominance of electric and magnetic forces over the gravitational one creates collective effects of internal collisions of particles in a substance.

In gases, the constituent particles are identical. Their thermal motion carried on a small distance due to the gravitational attraction. The structure of the plasma consists of electrons, ions and neutral particles, to their great charge and independent of each other. They may have different speed and temperature. In the end, there are waves and instability.

The interaction of the gases in two – (rarely three-particle). In plasma it is collective: the proximity of particles gives the opportunity for all groups to interact directly with all of you.

When collisions of particles in gases the velocity of the molecules are distributed according to Maxwell’s theory. It’s only a few of them are relatively high. In the plasma such movement occurs under the action of electric fields, and it is not only Maxwell. Often the presence of large velocity leads to a two-temperature distributions and the emergence of runaway electrons.

For a comprehensive description of the fourth state do not fit a smooth mathematical function and a probabilistic approach. Therefore, use of several mathematical models (usually at least three). This is usually fluid, liquid and Particle-In-Cell (method of particles in cells). But the information obtained this way is incomplete and requires further clarification.


Obtaining (creating) plasma:

In the laboratory there are several ways to obtain plasma. The first method is the strong heating of a selected substance, and a specific transition temperature in the plasma state depends on the structure of the electron shells of its atoms. The easier the electrons to leave their orbit, the less heat is required for the substance to transform into a plasma state. The effects can be subjected to any substance: solid, liquid, gaseous.

However, most often the plasma to create the electric fieldsthat accelerate electrons which in turn ionize atoms and plasma is heated very substance. For example, the gas is passed through an electric current creates a potential difference at the ends of the electrodes placed in the gas. Changing the parameters of current, it is possible to control the degree of ionization of the plasma. Note that although the discharge plasma and is heated by the current, but rapidly cools when interacting with uncharged particles of the surrounding gas.

Also required: the plasma state of matter it is possible to create a radiation exposure, a strong grip, laser radiation, resonant radiation, etc. ways.


Application of plasma:

In nature, opposing the solar wind magnetospheric plasma of the Earth protects the earth against the destructive effects of space. The ionosphere forms the substance of auroras, lightning, and corona.

The opening of the fourth state of matter has contributed to the development of many economic sectors. The properties of the ionosphere to reflect radio waves helped to establish the remote connection, to transmit data over long distances.

Laboratory gas discharges helped to create the gas-discharge light sources (fluorescent and other lamps), advanced TV panels and multimedia screens.

A controlled magnetic field and plasma jet steel processing, cutting and welding materials.

The phenomenon of plasma discharge has helped to build numerous switching devices, plasma torches, and even a specific space engines. Appeared plasma spraying and new possibilities of the surgery.

Also, scientists have created a toroidal chamber with surrounding electric magnets capable of holding a substance. It is controlled thermonuclear fusion. This electrical magnetic field is kept ionized gas under high temperature (deuterium-tritium plasma). This technology can be used in the construction of modern power plants, more environmentally friendly and safe compared to the nuclear counterparts.


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