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Encyclopedia > Plasma (physics)
Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation. The colors are a result of relaxation of electrons in excited states to lower energy states after they have recombined with ions. These processes emit light in a spectrum characteristic of the gas being excited.

In physics and chemistry, a plasma is typically an ionized gas. Plasma is considered to be a distinct state of matter, apart from gases, because of its unique properties. Ionized refers to presence of one or more free electrons, which are not bound to an atom or molecule. The free electric charges make the plasma electrically conductive so that it responds strongly to electromagnetic fields. Look up plasma in Wiktionary, the free dictionary. ... ImageMetadata File history File links Download high resolution version (1589x1609, 1106 KB) Khamis R A A plasma lamp. ... ImageMetadata File history File links Download high resolution version (1589x1609, 1106 KB) Khamis R A A plasma lamp. ... This article or section does not cite its references or sources. ... A current filament is an inhomogeneity in the current density distribution lateral to the direction of the current flow(current density vector). ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other uses, see Chemistry (disambiguation). ... In the physical sciences, a state of matter is one of the many ways that matter can interact with itself to form a macroscopic, homogenous phase. ... Gas phase particles (atoms, molecules, or ions) move around freely Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape and without a definite volume. ... Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... For other uses, see Electron (disambiguation). ... This box:      Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Not to be confused with electrical conductance, a measure of an objects or circuits ability to conduct an electric current between two points, which is dependent on the electrical conductivity and the geometric dimensions of the conducting object. ... The electromagnetic field is a physical field that is produced by electrically charged objects and which affects the behaviour of charged objects in the vicinity of the field. ...

Plasma typically takes the form of neutral gas-like clouds (e.g. stars) or charged ion beams, but may also include dust and grains (called dusty plasmas).[1] They are typically formed by heating and ionizing a gas, stripping electrons away from atoms, thereby enabling the positive and negative charges to move more freely. This article is about the astronomical object. ... An ion beam is a stream of charged particles, which has many uses in electronics manufacturing (principally ion implantation) and other industries. ... A dusty plasma is a plasma containing nano- or micro-sized particles suspended in it. ... Properties For other meanings of Atom, see Atom (disambiguation). ...

## History

Plasma arcs between the probes on a Wimshurst Machine. This device, invented in the early 1880s, has long been a popular laboratory demonstration of plasma.

This state of matter was first identified in a Crookes tube, and so described by Sir William Crookes in 1879 (he called it "radiant matter").[2] The nature of the Crookes tube "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897,[3] and dubbed "plasma" by Irving Langmuir in 1928,[4] perhaps because it reminded him of a blood plasma.[5] Langmuir wrote: Image File history File links Metadata No higher resolution available. ... Image File history File links Metadata No higher resolution available. ... Wimshurst machine with two Leyden jars. ... The Crookes tube is an evacuated glass cone with 3 node elements (one anode and two cathodes). ... Categories: People stubs | 1832 births | 1919 deaths | British scientists | English chemists | Physicists | Discoverer of a chemical element ... Year 1879 (MDCCCLXXIX) was a common year starting on Wednesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 12-day slower Julian calendar). ... A schematic diagram of a Crookes tube apparatus. ... Sir Joseph John â€œJ.J.â€ Thomson, OM, FRS (18 December 1856 â€“ 30 August 1940) was a British physicist and Nobel laureate, credited for the discovery of the electron and of isotopes, and the invention of the mass spectrometer. ... Irving Langmuir (January 31, 1881 in Brooklyn, New York - August 16, 1957 in Woods Hole, Massachusetts) was an American chemist and physicist. ... Blood plasma is the liquid component of blood, in which the blood cells are suspended. ...

Except near the electrodes, where there are sheaths containing very few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. We shall use the name plasma to describe this region containing balanced charges of ions and electrons."[4]

## Common plasmas

 Common forms of plasma include Artificially produced plasmas Those found in plasma displays, including TVs Inside fluorescent lamps (low energy lighting), neon signs [7] Rocket exhaust The area in front of a spacecraft's heat shield during reentry into the atmosphere Fusion energy research The electric arc in an arc lamp, an arc welder or plasma torch Plasma ball (sometimes called a plasma sphere or plasma globe) Plasmas used in semiconductor device fabrication including: Reactive Ion Etching, Sputtering, and Plasma Enhanced Chemical Vapor Deposition Terrestrial plasmas Space and astrophysical plasmas The Sun and other stars (which are plasmas heated by nuclear fusion) The solar wind The interplanetary medium (the space between the planets) The interstellar medium (the space between star systems) The Intergalactic medium (the space between galaxies) The Io-Jupiter flux-tube Accretion discs Interstellar nebulae

## Plasma properties and parameters

The Earth's "plasma fountain", showing oxygen, helium, and hydrogen ions which gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis-or plasma energy pouring back into the atmosphere.[8]

Image File history File links Plasma_fountain. ... Image File history File links Plasma_fountain. ... Aurora borealis Polar aurorae are optical phenomena characterized by colorful displays of light in the night sky. ...

### Definition of a plasma

Although a plasma is loosely described as an electrically neutral medium of positive and negative particles, a more rigorous definition requires three criteria to be satisfied:[citation needed]

1. The plasma approximation: Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just interacting with the closest particle (these collective effects are a distinguishing feature of a plasma). The plasma approximation is valid when the number of electrons within the sphere of influence (called the Debye sphere whose radius is the Debye screening length) of a particular particle is large. The average number of particles in the Debye sphere is given by the plasma parameter, "Λ" (the Greek letter Lambda).
2. Bulk interactions: The Debye screening length (defined above) is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place.
3. Plasma frequency: The electron plasma frequency (measuring plasma oscillations of the electrons) is large compared to the electron-neutral collision frequency (measuring frequency of collisions between electrons and neutral particles). When this condition is valid, plasmas act to shield charges very rapidly (quasineutrality is another defining property of plasmas).

In plasma physics, the Debye length, named after the Dutch physical chemist Peter Debye, is the scale over which mobile charge carriers (e. ... The plasma parameter is a number, denoted by capital Lambda, Î›, which measures the average number of electrons contained within a Debye sphere (a sphere of radius the Debye length) in a plasma (but note that the word parameter is usually used in plasma physics to refer to bulk plasma properties... Look up Î›, Î» in Wiktionary, the free dictionary. ... In plasma physics, plasma oscillations, also known as Langmuir waves (after Irving Langmuir) and plasma waves, are periodic oscillations of charge density in conducting media such as plasmas or metals. ...

### Ranges of plasma parameters

Plasma parameters can take on values varying by many orders of magnitude, but the properties of plasmas with apparently disparate parameters may be very similar (see plasma scaling). The following chart considers only conventional atomic plasmas and not exotic phenomena like quark gluon plasmas: An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... The parameters of plasmas, including their spatial and temporal extent, vary by many orders of magnitude. ... Quark gluon plasma is a phase of Quantum Chromodynamics (QCD) which exists at extremely high temperature and density. ...

Range of plasmas. Density increases upwards, temperature increases towards the right. The free electrons in a metal may be considered an electron plasma[9]
 Typical ranges of plasma parameters: orders of magnitude (OOM) Characteristic Terrestrial plasmas Cosmic plasmas Size in metres 10−6 m (lab plasmas) to 10² m (lightning) (~8 OOM) 10−6 m (spacecraft sheath) to 1025 m (intergalactic nebula) (~31 OOM) Lifetime in seconds 10−12 s (laser-produced plasma) to 107 s (fluorescent lights) (~19 OOM) 101 s (solar flares) to 1017 s (intergalactic plasma) (~17 OOM) Density in particles per cubic metre 107 m-3 to 1032 m-3 (inertial confinement plasma) 100 (i.e., 1) m-3 (intergalactic medium) to 1030 m-3 (stellar core) Temperature in kelvins ~0 K (crystalline non-neutral plasma[10]) to 108 K (magnetic fusion plasma) 10² K (aurora) to 107 K (solar core) Magnetic fields in teslas 10−4 T (lab plasma) to 10³ T (pulsed-power plasma) 10−12 T (intergalactic medium) to 1011 T (near neutron stars)

Image File history File links Download high-resolution version (738x727, 13 KB) The remarkable range of plasmas. ... Image File history File links Download high-resolution version (738x727, 13 KB) The remarkable range of plasmas. ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ...

### Degree of ionization

For plasma to exist, ionization is necessary. The word "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The degree of ionization of a plasma is the proportion of atoms which have lost (or gained) electrons, and is controlled mostly by the temperature. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e. respond to magnetic fields and be highly electrically conductive). The degree of ionization, α is defined as α = ni/(ni + na) where ni is the number density of ions and na is the number density of neutral atoms. The electron density is related to this by the average charge state <Z> of the ions through ne=<Z> ni where ne is the number density of electrons. Ionization is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. ... A Plasma lamp, illustrating a low degree of ionization (ie. ...

### Temperatures

Plasma temperature is commonly measured in kelvins or electronvolts, and is an informal measure of the thermal kinetic energy per particle. In most cases the electrons are close enough to thermal equilibrium that their temperature is relatively well-defined, even when there is a significant deviation from a Maxwellian energy distribution function, for example due to UV radiation, energetic particles, or strong electric fields. Because of the large difference in mass, the electrons come to thermodynamic equilibrium among themselves much faster than they come into equilibrium with the ions or neutral atoms. For this reason the "ion temperature" may be very different from (usually lower than) the "electron temperature". This is especially common in weakly ionized technological plasmas, where the ions are often near the ambient temperature. For other uses, see Kelvin (disambiguation). ... The electronvolt (symbol eV) is a unit of energy. ... In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann-distribution. ... James Clerk Maxwell (13 June 1831 â€“ 5 November 1879) was a Scottish mathematician and theoretical physicist. ... In physics, a particles distribution function is a function of seven variables, , which gives the number of particles per unit volume in phase space. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. ... If the velocities of a group of electrons, e. ... Room temperature, in laboratory reports, is taken to be roughly 21–23 degrees Celsius (68–72 degrees Fahrenheit), or 294–296 kelvins. ...

Based on the relative temperatures of the electrons, ions and neutrals, plasmas are classified as "thermal" or "non-thermal". Thermal plasmas have electrons and the heavy particles at the same temperature i.e. they are in thermal equilibrium with each other. Non-thermal plasmas on the other hand have the ions and neutrals at a much lower temperature (normally room temperature) whereas electrons are much "hotter".

Temperature controls the degree of plasma ionization. In particular, plasma ionization is determined by the "electron temperature" relative to the ionization energy (and more weakly by the density) in a relationship called the Saha equation. A plasma is sometimes referred to as being "hot" if it is nearly fully ionized, or "cold" if only a small fraction (for example 1%) of the gas molecules are ionized (but other definitions of the terms "hot plasma" and "cold plasma" are common). Even in a "cold" plasma the electron temperature is still typically several thousand degrees Celsius. Plasmas utilized in "plasma technology" ("technological plasmas") are usually cold in this sense. The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ... Developed by the Indian astrophysicist Meghnad Saha in 1920, this formula describes the degree of ionization of a gas as a function of the temperature T, density, and ionization energy. ...

### Potentials

Lightning is an example of plasma present at Earth's surface. Typically, lightning discharges 30,000 amperes, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays.[11] Plasma temperatures in lightning can approach ~28,000 kelvin (~27,700oC) and electron densities may exceed 1024/m³.

Since plasmas are very good conductors, electric potentials play an important role. The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the "plasma potential" or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas causes their electric fields to be very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma ($n_e=langle Zrangle n_i$), but on the scale of the Debye length there can be charge imbalance. In the special case that double layers are formed, the charge separation can extend some tens of Debye lengths. Image File history File linksMetadata Download high resolution version (2048x3072, 3589 KB) This is a rotated version of Lightning over Oradea Romania. ... Image File history File linksMetadata Download high resolution version (2048x3072, 3589 KB) This is a rotated version of Lightning over Oradea Romania. ... Not to be confused with lighting. ... The Debye sheath (also electrostatic sheath) is the non-neutral layer several Debye lengths thick where a plasma contacts a material surface. ...

The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the "Boltzmann relation": Charge density is the amount of electric charge per unit volume. ... In a plasma, the Boltzmann relation connects the electron density ne to the plasma potential φpl as follows: ne = n0 exp(eφpl/kBTe) The reference for the potential potential is taken to be a position where the electron density is n0. ...

$n_e propto e^{ePhi/k_BT_e}$.

Differentiating this relation provides a means to calculate the electric field from the density:

$vec{E} = (k_BT_e/e)(nabla n_e/n_e)$.

It is possible to produce a plasma which is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise it will be dissipated by the repulsive electrostatic force. In physics, the electrostatic force is the force arising between static (that is, non-moving) electric charges. ...

In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances (ie. greater than the Debye length). But the existence of charged particles causes the plasma to generate and be affected by magnetic fields. This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object which separates charge over a few tens of Debye lengths. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics. Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... Screening is the damping of electric fields caused by the presence of mobile charge carriers. ... In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... In plasma physics, the Debye length, named after the Dutch physical chemist Peter Debye, is the scale over which mobile charge carriers (e. ... For the indie-pop band, see The Magnetic Fields. ... In plasma physics, the Debye length, named after the Dutch physical chemist Peter Debye, is the scale over which mobile charge carriers (e. ... For the indie-pop band, see The Magnetic Fields. ... This is a list of academic disciplines (and academic fields). ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ...

### Magnetization

A plasma in which the magnetic field is strong enough to influence the motion of the charged particles is said to be magnetized. A common quantitative criterion is that a particle on average completes at least one gyration around the magnetic field before making a collision (ie. ωce / νcoll > 1 where ωce is the "electron gyrofrequency" and νcoll is the "electron collision rate"). It is often the case that the electrons are magnetized while the ions are not. Magnetized plasmas are anisotropic, meaning that their properties in the direction parallel to the magnetic field are different from those perpendicular to it. While electric fields in plasmas are usually small due to the high conductivity, the electric field associated with a plasma moving in a magnetic field is given by E = -v x B (where E is the electric field, v is the velocity, and B is the magnetic field), and is not affected by Debye shielding.[12] This article is being considered for deletion in accordance with Wikipedias deletion policy. ... Screening is the damping of electric fields caused by the presence of mobile charge carriers. ...

### Comparison of plasma and gas phases

Plasma is often called the fourth state of matter. It is distinct from other lower-energy states of matter; most commonly solid, liquid, and gas, although it is closely related to the gas phase in that it also has no definite form or volume. Physicists consider a plasma to be more than a gas[citation needed] because of a number of distinct properties including the following: In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... This box:      For other uses, see Solid (disambiguation). ... For other uses, see Liquid (disambiguation). ... Gas phase particles (atoms, molecules, or ions) move around freely Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape and without a definite volume. ...

 Property Gas Plasma Electrical Conductivity Very low Air is an excellent insulator until it breaks down into plasma at electric field strengths above 30 kilovolts per centimeter.[13] Usually very high For many purposes the conductivity of a plasma may be treated as infinite. Independently acting species One All gas particles behave in a similar way, influenced by gravity, and collisions with one another Two or three Electrons, ions, and neutrals can be distinguished by the sign of their charge so that they behave independently in many circumstances, with different bulk velocities and temperatures, allowing phenomena such as new types of waves and instabilities Velocity distribution Maxwellian Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles. Often non-Maxwellian Collisional interactions are often weak in hot plasmas, and external forcing can drive the plasma far from local equilibrium, and lead to a significant population of unusually fast particles. Interactions Binary Two-particle collisions are the rule, three-body collisions extremely rare. Collective Waves, or organised motion of plasma, are very important because the particles can interact at long ranges through the electric and magnetic forces.

Not to be confused with electrical conductance, a measure of an objects or circuits ability to conduct an electric current between two points, which is dependent on the electrical conductivity and the geometric dimensions of the conducting object. ... Electrical conductivity is a measure of how well a material accommodates the transport of electric charge. ... Gravity is a force of attraction that acts between bodies that have mass. ... For other uses, see Collision (disambiguation). ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... ... This box:      Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Waves in plasmas are an interconnected set of particles and fields which propagates in a periodically repeating fashion. ... Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. ... The Maxwell-Boltzmann distribution is a probability distribution with applications in physics and chemistry. ...

## Complex plasma phenomena

The remnant of "Tycho's Supernova", a huge ball of expanding plasma. The blue outer shell arises from X-ray emission by high-speed electrons.

Although the underlying equations governing plasmas are relatively simple, plasma behaviour is extraordinarily varied and subtle: the emergence of unexpected behaviour from a simple model is a typical feature of a complex system. Such systems lie in some sense on the boundary between ordered and disordered behaviour, and cannot typically be described either by simple, smooth, mathematical functions, or by pure randomness. The spontaneous formation of interesting spatial features on a wide range of length scales is one manifestation of plasma complexity. The features are interesting, for example, because they are very sharp, spatially intermittent (the distance between features is much larger than the features themselves), or have a fractal form. Many of these features were first studied in the laboratory, and have subsequently been recognised throughout the universe. Examples of complexity and complex structures in plasmas include: Image File history File links Download high resolution version (2400x2400, 609 KB) Summary Tychos Supernova Remnant. ... Image File history File links Download high resolution version (2400x2400, 609 KB) Summary Tychos Supernova Remnant. ... Remnant of Keplers Supernova, SN 1604 Remnant of Tychos Nova, SN 1572 A supernova remnant (SNR) is the structure resulting from the gigantic explosion of a star in a supernova. ... X-ray image of the expanding cloud of debris and high energy electrons from Tychos supernova. ... There are many definitions of complexity, therefore many natural, artificial and abstract objects or networks can be considered to be complex systems, and their study (complexity science) is highly interdisciplinary. ... The boundary of the Mandelbrot set is a famous example of a fractal. ...

### Filamentation

The striations or "stringy" things,[14] seen in many plasmas, like the plasma ball (image above), the aurora,[15] lightning,[16] electric arcs, solar flares,[17] and supernova remnants[18] They are sometimes associated with larger current densities, and are also called magnetic ropes.[19] (See also Plasma pinch) The Aurora Borealis, or Northern Lights, shines above Bear Lake Aurora Borealis as seen over Canada at 11,000m (36,000 feet) Red and green Aurora in Fairbanks, Alaska Aurora Borealis redirects here. ... Not to be confused with lighting. ... A 3000 volt electricity arc between two nails Electricity arcs between the power rail and electrical pickup shoe on a London Underground train An electric arc can melt calcium oxide An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current... A solar flare is a violent explosion in the Suns atmosphere with an energy equivalent to tens of millions of hydrogen bombs. ... Remnant of Keplers Supernova, SN 1604 Remnant of Tychos Nova, SN 1572 A supernova remnant (SNR) is the structure resulting from the gigantic explosion of a star in a supernova. ... Lightning bolts illustrating electromagnetically pinched plasma filaments A pinch is a phenomenon that may occur in a current-carrying plasma whose magnetic field constricts or pinches the plasma, and is associated with filamenation and particle beams. ...

### Shocks or double layers

Narrow sheets with sharp gradients, such as shocks or double layers which support rapid changes in plasma properties. Double layers involve localised charge separation, which causes a large potential difference across the layer, but does not generate an electric field outside the layer. Double layers separate adjacent plasma regions with different physical characteristics, and are often found in current carrying plasmas. They accelerate both ions and electrons.

### Electric fields and circuits

Quasineutrality of a plasma requires that plasma currents close on themselves in electric circuits. Such circuits follow Kirchhoff's circuit laws, and possess a resistance and inductance. These circuits must generally be treated as a strongly coupled system, with the behaviour in each plasma region dependent on the entire circuit. It is this strong coupling between system elements, together with nonlinearity, which may lead to complex behaviour. Electrical circuits in plasmas store inductive (magnetic) energy, and should the circuit be disrupted, for example, by a plasma instability, the inductive energy will be released as plasma heating and acceleration. This is a common explanation for the heating which takes place in the solar corona. Electric currents, and in particular, magnetic-field-aligned electric currents (which are sometimes generically referred to as "Birkeland currents"), are also observed in the Earth's aurora, and in plasma filaments. Not to be confused with Kerckhoffs principle. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Î¦ through the circuit. ... The corona is the luminous plasma atmosphere of the Sun extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... The aurora on Jupiter, powered by Jovian Birkeland currents [Ref. ...

### Cellular structure

Narrow sheets with sharp gradients may separate regions with different properties such as magnetization, density, and temperature, resulting in cell-like regions. Examples include the magnetosphere, heliosphere, and heliospheric current sheet. Hannes Alfvén wrote: "From the cosmological point of view, the most important new space research discovery is probably the cellular structure of space. As has been seen, in every region of space which is accessible to in situ measurements, there are a number of 'cell walls', sheets of electric currents, which divide space into compartments with different magnetization, temperature, density, etc ."[20] A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. ... The heliosphere is a bubble in space produced by the solar wind. ... Heliospheric current sheet The Heliospheric current sheet (HCS) is the surface within the Solar System where the polarity of the Suns magnetic field changes from north to south. ...

### Critical ionization velocity

The Critical ionization velocity is the relative velocity between an (magnetized) ionized plasma and a neutral gas above which a runaway ionization process takes place. The critical ionization process is a quite general mechanism for the conversion of the kinetic energy of a rapidly streaming gas into ionization and plasma thermal energy. Critical phenomena in general are typical of complex systems, and may lead to sharp spatial or temporal features. Critical ionization velocity experiment onboard space shuttle Discovery (STS-39), releasing a plume of nitrous oxide gas. ...

### Ultracold plasma

It is possible to create ultracold plasmas, by using lasers to trap and cool neutral atoms to temperatures of 1 mK or lower. Another laser then ionizes the atoms by giving each of the outermost electrons just enough energy to escape the electrical attraction of its parent ion. To help compare different orders of magnitude this page lists temperatures between 1 millikelvin and 1 kelvin. ...

The key point about ultracold plasmas is that by manipulating the atoms with lasers, the kinetic energy of the liberated electrons can be controlled. Using standard pulsed lasers, the electron energy can be made to correspond to a temperature of as low as 0.1 K,­ a limit set by the frequency bandwidth of the laser pulse. The ions, however, retain the millikelvin temperatures of the neutral atoms. This type of non-equilibrium ultracold plasma evolves rapidly, and many fundamental questions about its behaviour remain unanswered. Experiments conducted so far have revealed surprising dynamics and recombination behavior which are pushing the limits of our knowledge of plasma physics.[citation needed] One of the metastable states of strongly nonideal plasma is Rydberg matter which forms upon condensation of excited atoms. Rydberg matter is a metastable state of highly excited atoms (see Rydberg atom) which are condensed in a solid- or liquid-like very low density matter. ...

### Non-neutral plasma

The strength and range of the electric force and the good conductivity of plasmas usually ensure that the density of positive and negative charges in any sizeable region are equal ("quasineutrality"). A plasma which has a significant excess of charge density or which is, in the extreme case, composed of only a single species, is called a non-neutral plasma. In such a plasma, electric fields play a dominant role. Examples are charged particle beams, an electron cloud in a Penning trap, and positron plasmas.[21] A particle beam is an accelerated stream of charged particles or atoms (often moving at very near the speed of light) which may be directed by magnets and focused by electrostatic lenses, although they may also be self-focusing (see Pinch). ... Penning traps are devices for the storage of charged particles using a constant magnetic field and a constant electric field. ...

### Dusty plasma and grain plasma

A dusty plasma is one containing tiny charged particles of dust (typically found in space) which also behaves like a plasma. A plasma containing larger particles is called a grain plasma. A dusty plasma is a plasma containing nano- or micro-sized particles suspended in it. ...

## Mathematical descriptions

The complex self-constricting magnetic field lines and current paths in a field-aligned Birkeland current which may develop in a plasma[22]
Main article: Plasma modeling

To completely describe the state of a plasma, we would need to write down all the particle locations and velocities, and describe the electromagnetic field in the plasma region. However, it is generally not practical or necessary to keep track of all the particles in a plasma. Therefore, plasma physicists commonly use less detailed descriptions known as models, of which there are two main types: Image File history File links Download high-resolution version (560x800, 27 KB) The self-constricting magnetic field lines and current paths in a Birkeland current (or magnetic rope). ... Image File history File links Download high-resolution version (560x800, 27 KB) The self-constricting magnetic field lines and current paths in a Birkeland current (or magnetic rope). ... The aurora on Jupiter, powered by Jovian Birkeland currents [Ref. ... This article or section does not cite its references or sources. ...

### Fluid model

Fluid models describe plasmas in terms of smoothed quantities like density and averaged velocity around each position (see Plasma parameters). One simple fluid model, magnetohydrodynamics, treats the plasma as a single fluid governed by a combination of Maxwell's Equations and the Navier-Stokes Equations. A more general description is the two-fluid picture, where the ions and electrons are described separately. Fluid models are often accurate when collisionality is sufficiently high to keep the plasma velocity distribution close to a Maxwell-Boltzmann distribution. Because fluid models usually describe the plasma in terms of a single flow at a certain temperature at each spatial location, they can neither capture velocity space structures like beams or double layers nor resolve wave-particle effects. The complex self-constricting magnetic field lines and current paths in a Birkeland current that may develop in a plasma (Evolution of the Solar System, 1976) Plasma parameters define various characteristics of a plasma, an electrically-conductive collection of charged particles that responds collectively to electromagnetic forces. ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ... For thermodynamic relations, see Maxwell relations. ... The Navier-Stokes equations, named after Claude-Louis Navier and George Gabriel Stokes, are a set of equations which describe the motion of fluid substances such as liquids and gases. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Saturnian aurora whose reddish colour is characteristic of ionized hydrogen plasma. ...

### Kinetic model

Kinetic models describe the particle velocity distribution function at each point in the plasma, and therefore do not need to assume a Maxwell-Boltzmann distribution. A kinetic description is often necessary for collisionless plasmas. There are two common approaches to kinetic description of a plasma. One is based on representing the smoothed distribution function on a grid in velocity and position. The other, known as the particle-in-cell (PIC) technique, includes kinetic information by following the trajectories of a large number of individual particles. Kinetic models are generally more computationally intensive than fluid models. The Vlasov equation may be used to describe how a system of particles evolves in an electromagnetic environment. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Particle-In-Cell (PIC) is an algorithm to compute (for example) the trajectories of charged particles in an electromagnetic field. ... The Boltzmann equation, devised by Ludwig Boltzmann, describes the statistical distribution of particles in a fluid. ...

## Common artificial plasma

Most artificial plasmas are generated by the application of electric and/or magnetic fields. Plasma generated in a laboratory setting and for industrial use can be generally categorized by:

• The type of power source used to generate the plasma; DC, RF and microwave.
• The pressure at which they operate; vacuum pressure (< 10 mTorr), moderate pressure (~ 1 Torr), and atmospheric pressure (760 Torr).
• The degree of ionization within the plasma; fully ionized, partially ionized, weakly ionized.
• The temperature relationships within the plasma; Thermal plasma (Te = Tion = Tgas), Non-Thermal or "cold" plasma (Te >> Tion = Tgas)
• The electrode configuration used to generate the plasma.
• The magnetization of the particles within the plasma; Magnetized (both ion and electrons are trapped in Larmor orbits by the magnetic field), partially magnetized (the electrons but not the ions are trapped by the magnetic field), non-magnetized (the magnetic field is too weak to trap the particles in orbits but may generate Lorentz forces).
• Its application

The gyroradius (also known as radius of gyration or cyclotron radius) defines the radius of the circular motion of a charged particle in the presence of a magnetic field. ...

### Examples of industrial/commercial plasma

#### Low-pressure discharges

Glow discharge plasmas: Non-thermal plasmas generated by the application of DC or low frequency RF (<100 kHz) electric field to the gap between two metal electrodes. Probably the most common plasma; this is the type of plasma generated within fluorescent light tubes.
Capacitively coupled plasma (CCP): Similar to glow discharge plasmas, but generated with high frequency RF electric fields, typically 13.56 MHz. It differs from Glow discharges in that the sheaths are much less intense. These are widely used in the microfabrication and integrated circuit manufacturing industries for plasma etching and plasma enhanced chemical vapor deposition.
Inductively Coupled Plasmas (ICP): Similar to a CCP and with similar applications but the electrode consists of a coil wrapped around the discharge volume which inductively excites the plasma. Electric glow discharge is a type of plasma formed by passing a current at 100V to several kV through a gas - usually argon or another noble gas. ... Capacitively coupled plasma: A capacitively coupled plasma (CCP) is one of the most common types of industrial plasma reactors. ...

#### Atmospheric pressure

Arc discharge: This is a high power thermal discharge of very high temperature ~10,000 K. It can be generated using various power supplies. It is commonly used in metallurgical processes. For example it is used to melt rocks containing Al2O3 to produce aluminum.
Corona discharge: This is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in ozone generators and particle precipitators.
Dielectric Barrier Discharge (DBD): Invented by Siemens[citation needed], this is a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled 'Corona' discharge in industry and has similar application to Corona Discharges. It is also widely used in the web treatment of fabrics. The application of the discharge to synthetic fabrics and plastics functionalizes the surface and allows for paints, glues and similar materials to adhere. An electric arc can melt calcium oxide. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... In electricity, a corona discharge is an electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient exceeds a certain value, in situations where sparking (also known as arcing) is not favoured. ... For other uses, see Ozone (disambiguation). ... Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric barrier. ... Siemens has the following uses: Siemens is a German family name carried by generations of the telecommunications industrialists, including Werner von Siemens, Sir William Siemens, Wilhelm von Siemens and Peter von Siemens Siemens AG is a German electrical and telecommunications company, founded as a telegraph equipment manufacturer by Werner von...

## Fields of active research

Hall effect thruster. The electric field in a plasma double layer is so effective at accelerating ions that electric fields are used in ion drives

This is just a partial list of topics. A more complete and organized list can be found on the Web site for Plasma science and technology.[23] Image of a Hall thruster in operation. ... Image of a Hall thruster in operation. ... 2 kW Laboratory Hall Thruster in operation at the Princeton Plasma Physics Laboratory A Hall effect thruster is a type of ion thruster in which the propellant is accelerated by an electric field in a plasma discharge with a radial magnetic field. ... Saturnian aurora whose reddish colour is characteristic of ionized hydrogen plasma. ... An ion engine test An ion thruster is a type of spacecraft propulsion that uses beams of ions for propulsion. ...

 Plasma theory Plasma equilibria and stability Plasma interactions with waves and beams Guiding center Adiabatic invariant Debye sheath Coulomb collision Plasmas in nature The Earth's ionosphere Space plasmas, e.g. Earth's plasmasphere (an inner portion of the magnetosphere dense with plasma) Astrophysical plasma Industrial plasmas Plasma chemistry Plasma processing Plasma Spray Plasma display Plasma sources Dusty Plasmas Plasma diagnostics Plasma applications Fusion power Magnetic fusion energy (MFE) — tokamak, stellarator, reversed field pinch, magnetic mirror, dense plasma focus Inertial fusion energy (IFE) (also Inertial confinement fusion — ICF) Plasma-based weaponry Ion implantation Plasma ashing Food processing (Nonthermal plasma) Plasma arc waste disposal, convert waste into reusable material with plasma. Plasma acceleration

## Footnotes

1. ^ Greg Morfill et al, Focus on Complex (Dusty) Plasmas (2003) New J. Phys. 5
2. ^ Crookes presented a lecture to the British Association for the Advancement of Science, in Sheffield, on Friday, 22 August 1879 [1] [2]
3. ^ Announced in his evening lecture to the Royal Institution on Friday, 30th April 1897, and published in Philosophical Magazine, 44, 293 [3]
4. ^ a b I. Langmuir, "Oscillations in ionized gases," Proc. Nat. Acad. Sci. U.S., vol. 14, p. 628, 1928
5. ^ G. L. Rogoff, Ed., IEEE Transactions on Plasma Science, vol. 19, p. 989, Dec. 1991. See extract at http://www.plasmacoalition.org/what.htm
6. ^ It is often stated that more than 99% of the universe is plasma. See, for example, D. A. Gurnett, A. Bhattacharjee, Introduction to Plasma Physics: With Space and Laboratory Applications (2005) (Page 2) and also K Scherer, H Fichtner, B Heber, "Space Weather: The Physics Behind a Slogan" (2005) (Page 138). Essentially all of the visible light from space comes from stars, which are plasmas with a temperature such that they radiate strongly at visible wavelengths. Most of the ordinary (or baryonic) matter in the universe, however, is found in the intergalactic medium, which is also a plasma, but much hotter, so that it radiates primarily as x-rays. The current scientific consensus is that about 96% of the total energy density in the universe is not plasma or any other form of ordinary matter, but a combination of cold dark matter and dark energy.
7. ^ IPPEX Glossary of Fusion Terms
8. ^ Plasma fountain Source, press release: Solar Wind Squeezes Some of Earth's Atmosphere into Space
9. ^ After Peratt, A. L., "Advances in Numerical Modeling of Astrophysical and Space Plasmas" (1966) Astrophysics and Space Science, v. 242, Issue 1/2, p. 93-163.
10. ^ See The Nonneutral Plasma Group at the University of California, San Diego
11. ^ See Flashes in the Sky: Earth's Gamma-Ray Bursts Triggered by Lightning
12. ^ Richard Fitzpatrick, Introduction to Plasma Physics, Magnetized plasmas
13. ^ Hong, Alice (2000). Dielectric Strength of Air. The Physics Factbook.
14. ^ Dickel, J. R., "The Filaments in Supernova Remnants: Sheets, Strings, Ribbons, or?" (1990) Bulletin of the American Astronomical Society, Vol. 22, p.832
15. ^ Grydeland, T., et al, "Interferometric observations of filamentary structures associated with plasma instability in the auroral ionosphere" (2003) Geophysical Research Letters, Volume 30, Issue 6, pp. 71-1
16. ^ Moss, Gregory D., et al, "Monte Carlo model for analysis of thermal runaway electrons in streamer tips in transient luminous events and streamer zones of lightning leaders" (2006) Journal of Geophysical Research, Volume 111, Issue A2, CiteID A02307
17. ^ Doherty, Lowell R., "Filamentary Structure in Solar Prominences." (1965) Astrophysical Journal, vol. 141, p.251
18. ^ Hubble views the Crab Nebula M1: The Crab Nebula Filaments
19. ^ Zhang, Yan-An, et al, "A rope-shaped solar filament and a IIIb flare" (2002) Chinese Astronomy and Astrophysics, Volume 26, Issue 4, p. 442-450
20. ^ Hannes Alfvén, Cosmic Plasma (1981) See section VI.13.1. Cellular Structure of Space.
21. ^ R. G. Greaves, M. D. Tinkle, and C. M. Surko, "Creation and uses of positron plasmas", Physics of Plasmas -- May 1994 -- Volume 1, Issue 5, pp. 1439-1446
22. ^ See Evolution of the Solar System, 1976)
23. ^ Web site for Plasma science and technology

A lecture on linear algebra at the Helsinki University of Technology A lecture is an oral presentation intended to teach people about a particular subject, for example by a university or college teacher. ... The British Association or the British Association for the Advancement of Science or the BA is a learned society with the object of promoting science, directing general attention to scientific matters, and facilitating intercourse between scientific workers. ... is the 234th day of the year (235th in leap years) in the Gregorian calendar. ... Year 1879 (MDCCCLXXIX) was a common year starting on Wednesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 12-day slower Julian calendar). ... The Royal Institution of Great Britain was set up in 1799 by the leading British scientists of the age, including Henry Cavendish and its first president George Finch, the 9th Earl of Winchilsea, for diffusing the knowledge, and facilitating the general introduction, of useful mechanical inventions and improvements; and for... The Philosophical Magazine is arguably the worldâ€™s oldest commercially published scientific journal. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... Intergalactic space is the physical space between galaxies. ... Cold dark matter (or CDM) is a refinement of the big bang theory, as well as being one possible variation of the more generic Dark Matter theory. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ...

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Image File history File links Portal. ... Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 151 languages. ... Image File history File links Commons-logo. ... There are very few or no other articles that link to this one. ... The complex self-constricting magnetic field lines and current paths in a Birkeland current that may develop in a plasma (Evolution of the Solar System, 1976) Plasma parameters define various characteristics of a plasma, an electrically-conductive collection of charged particles that responds collectively to electromagnetic forces. ... Magnetohydrodynamics (MHD) (magnetofluiddynamics or hydromagnetics) is the academic discipline which studies the dynamics of electrically conducting fluids. ... Screening is the damping of electric fields caused by the presence of mobile charge carriers. ... Alexei Alexeyevich Abrikosov Hannes AlfvÃ©n - Received the only Nobel Prize specifically for contributions to plasma physics. ... This is a list of important publications in physics, organized by field. ... The logo of the IEEE Nuclear and Plasma Sciences Society The IEEE Nuclear and Plasma Sciences Society (NPSS) is a transnational group of about 3000 professional engineers and scientists. ...

Results from FactBites:

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