Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation. Plasma lamps (also variously plasma globes balls domes spheres or orbs are Novelty items which were most popular in the 1980s A current filament is an inhomogeneity in the Current density distribution lateral to the of the current flow (that is orthogonal to the current density vector 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. A spectrum (plural spectra or spectrums) is a condition that is not limited to a specific set of values but can vary infinitely within a continuum.

In physical and chemical usage, plasma refers to an ionized gas, in which a certain proportion of electrons are free, rather than being bound to an atom or molecule. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge This page is about the physical properties of gas as a state of matter The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by The ability of the positive and negative charges to move somewhat independently makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. The electromagnetic field is a physical field produced by electrically charged objects. Plasma therefore has properties quite unlike those of solids, liquids or gases and is considered to be a distinct state of matter. A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of This page is about the physical properties of gas as a state of matter A state of matter (or physical state, or form of matter) has physical properties which are qualitatively different from other states of matter Plasma typically takes the form of neutral gas-like clouds (e. g. stars). A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth

History

Plasma arcs between the probes on a Wimshurst Machine. The Wimshurst machine is an electrostatic device for generating high Voltages developed between 1880 and 1883 by British Inventor James Wimshurst 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"). A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays Sir William Crookes, OM, FRS (17 June 1832 – 4 April 1919 was an English Chemist and Physicist. Year 1879 ( MDCCCLXXIX) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common ^[1] The nature of the Crookes tube "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897,^[2] and dubbed "plasma" by Irving Langmuir in 1928,^[3] perhaps because it reminded him of a blood plasma. Cathode rays (also called an electron beam or e-beam) are streams of Electrons observed in Vacuum tubes i Sir Joseph John “JJ” Thomson, OM, FRS (18 December 1856 &ndash 30 August 1940 was a British Physicist and Nobel laureate Irving Langmuir ( January 31, 1881 in Brooklyn New York – August 16, 1957 in Woods Hole Massachusetts) was an Blood plasma is the Liquid component of Blood, in which the Blood cells are suspended ^[4] Langmuir wrote:

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. "^[3]

Common plasmas

Plasmas are by far the most common phase of matter in the universe, both by mass and by volume. 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 ^[5] All the stars are made of plasma, and even the space between the stars is filled with a plasma, albeit a very sparse one (See astrophysical plasma, interstellar medium and intergalactic space). A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth An astrophysical plasma is a plasma (an ionized gas found in astronomy whose physical properties are studied in the science of Astrophysics. Intergalactic space is the physical space between galaxies. Generally free of dust and debris intergalactic space is very close to a total Vacuum. In the solar system, the planet Jupiter accounts for most of the non-plasma, only about 0. 1% of the mass and 10⁻¹⁵% of the volume within the orbit of Pluto. Notable plasma physicist Hannes Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of plasma (see dusty plasmas). Hannes Olof Gösta Alfvén ( May 30, 1908; Norrköping, Sweden &ndash April 2, 1995; Djursholm, Sweden A dusty plasma is a plasma containing nanometer or micrometer-sized particles suspended in it

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. A plasma display panel (PDP is a type of Flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor. Neon signs are luminous-tube signs that contain neon or other inert gases at a low pressure A spacecraft is a Vehicle or machine designed for Spaceflight. A heat shield is a protective layer on a Spacecraft or Ballistic missile that is designed to protect it from the high Temperature of Atmospheric Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five OZONE is an object oriented Operating system written in the C programming language. Fusion power is power generated by Nuclear fusion reactions In this kind of reaction two light atomic nuclei fuse An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive Welding is a fabrication process that joins materials usually Metals or Thermoplastics by causing coalescence. A plasma torch (or plasma arc or plasma gun) is a device that generates a directed flow of plasma from its nozzle Plasma lamps (also variously plasma globes balls domes spheres or orbs are Novelty items which were most popular in the 1980s Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic Reactive ion etching ( RIE) is an etching technology used in Microfabrication. Sputtering is a process whereby Atoms are Ejected from a solid target material due to bombardment of the target by energetic Ions It is commonly used for Plasma Enhanced Chemical Vapor Deposition (PECVD is a process used to deposit thin films from a Gas state ( Vapor) to a Solid state on some substrate EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or Ball lightning is an atmospheric electrical phenomenon the physical nature of which is still Controversial. St Elmo's fire is an electrical Weather Phenomenon in which luminous plasma is created by a Coronal discharge originating from Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation Astrophysics is the branch of Astronomy that deals with the Physics of the Universe, including the physical properties ( Luminosity, The Sun (Sol is the Star at the center of the Solar System. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as Planets Asteroids Intergalactic space is the physical space between galaxies. Generally free of dust and debris intergalactic space is very close to a total Vacuum. TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek An accretion disc (or accretion disk) is a structure (often a Circumstellar disk) formed by diffuse material in orbital motion around a central body A nebula (from Latin: "mist" pl nebulae or nebulæ, with ligature or nebulas) is an Interstellar cloud of Plasma Fountain is in the North Pole of the Earth. This figure depicts the Oxygen, Helium, and Hydrogen Ions that gush into space 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. ^[7]

Definition of a plasma

Although a plasma is loosely described as an electrically neutral medium of positive and negative particles, a definition can have three criteria:^[8][9][10]

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. In Plasma physics, the Debye length (also called Debye radius) named after the Dutch physicist and physical chemist Peter Debye, is the scale over which The average number of particles in the Debye sphere is given by the plasma parameter, "Λ" (the Greek letter Lambda). The plasma parameter is a dimensionless number denoted by capital Lambda Λ which measures the average number of electrons contained within a Debye sphere (a sphere of radius The Greek alphabet (Ελληνικό αλφάβητο is a set of twenty-four letters that has been used to write the Greek language since the late 9th or early Lambda (uppercase Λ, lowercase λ; Λάμβδα or el Λάμδα Lamda is the 11th letter of the Greek alphabet.
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). Plasma oscillations, also known as " Langmuir waves " (after Irving Langmuir) are rapid oscillations of the electron density in conducting media such as When this condition is valid, plasmas act to shield charges very rapidly (quasineutrality is another defining property of plasmas).

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). 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. The following chart considers only conventional atomic plasmas and not exotic phenomena like quark gluon plasmas:

Range of plasmas. A quark-gluon plasma (QGP is a phase of Quantum chromodynamics (QCD which exists at extremely high Temperature and/or Density. Density increases upwards, temperature increases towards the right. The free electrons in a metal may be considered an electron plasma^[11]

Degree of ionization

For plasma to exist, ionization is necessary. Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons The term "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. The degree of ionization refers to the proportion of neutral particles such as those in a Gas or aqueous solution that are ionized into charged particles 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 = n_i/(n_i + n_a) where n_i is the number density of ions and n_a is the number density of neutral atoms. The electron density is related to this by the average charge state <Z> of the ions through n_e=<Z> n_i where n_e is the number density of electrons.

Temperatures

Plasma temperature is commonly measured in kelvins or electronvolts, and is an informal measure of the thermal kinetic energy per particle. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic 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. In Thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium Mechanical equilibrium, and James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. This article describes the distribution function as used in physics Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays 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 (that can 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". If the velocities of a group of Electrons eg in a plasma, follow a Maxwell-Boltzmann distribution, then the electron temperature is well-defined This is especially common in weakly ionized technological plasmas, where the ions are often near the ambient temperature. Room temperature (also referred to as ambient temperature) is a common term to denote a certain Temperature within enclosed space at which humans are accustomed

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. The ionization potential, ionization energy or EI of an Atom or Molecule is the Energy required to remove an Electron The Saha ionization equation, also known as the Saha-Langmuir equation, was developed by the Indian astrophysicist Megh Nad Saha in 1920 and later (1923 by 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.

Potentials

Lightning is an example of plasma present at Earth's surface. Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or Typically, lightning discharges 30,000 amperes, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays. ^[13] Plasma temperatures in lightning can approach ~28,000 kelvin (~27,700°C) 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 Debye sheath (also electrostatic sheath) is a layer in a plasma which has a greater density of positive ions and hence an overall excess positive charge that 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 (), 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. A double layer is a Structure in a plasma and consists of two parallel layers with opposite electrical charge

The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. The linear surface or volume charge density is the amount of Electric charge in a line, Surface, or Volume. A common example is to assume that the electrons satisfy the "Boltzmann relation":

. In a plasma, the Boltzmann relation connects the electron density n e to the plasma potential &phipl as follows n

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

.

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. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form

In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances (ie. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study 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 (that can greater than the Debye length). In Plasma physics, the Debye length (also called Debye radius) named after the Dutch physicist and physical chemist Peter Debye, is the scale over which But the existence of charged particles causes the plasma to generate and be affected by magnetic fields. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges 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. In Plasma physics, the Debye length (also called Debye radius) named after the Dutch physicist and physical chemist Peter Debye, is the scale over which The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges An academic discipline or field of study is a branch of Knowledge which is taught or Researched at the college or university level Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically

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. ω_ce / ν_coll > 1 where ω_ce is the "electron gyrofrequency" and ν_coll 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. Anisotropy (pronounced with stress on the third syllable ˌænaɪˈsɒtrəpi is the property of being directionally dependent as opposed to Isotropy, which means homogeneity 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. Screening is the damping of Electric fields caused by the presence of mobile charge carriers ^[14]

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. A state of matter (or physical state, or form of matter) has physical properties which are qualitatively different from other states of matter A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of This page is about the physical properties of gas as a state of matter Physicists consider a plasma to be more than a gas because of a number of distinct properties including the following:

Complex plasma phenomena

The remnant of "Tycho's Supernova", a huge ball of expanding plasma. A supernova remnant ( SNR) is the structure resulting from the gigantic explosion of a Star in a Supernova. SN 1572 ( Tycho's Supernova, Tycho's Nova) "B Cassiopeiae" (B Cas or 3C 10 was a Supernova of Type Ia in the 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. This article describes complex system as a type of system For other meanings see Complex systems. 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. A fractal is generally "a rough or fragmented geometric shape that can be split into parts each of which is (at least approximately a reduced-size copy of the whole" 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:

Filamentation

The striations or "stringy" things,^[16] seen in many plasmas, like the plasma ball (image above), the aurora,^[17] lightning,^[18] electric arcs, solar flares,^[19] and supernova remnants^[20] They are sometimes associated with larger current densities, and are also called magnetic ropes. Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares A supernova remnant ( SNR) is the structure resulting from the gigantic explosion of a Star in a Supernova. ^[21] (See also Plasma pinch)

Shocks or double layers

Narrow sheets with sharp gradients, such as shocks or double layers which support rapid changes in plasma properties. A pinch is the compression of an electrically conducting filament by magnetic forces A double layer is a Structure in a plasma and consists of two parallel layers with opposite electrical charge 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. For other laws named after Gustav Kirchhoff, see Kirchhoff's laws. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting 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. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily 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. A Birkeland current is a specific magnetic field aligned current in the Earth’s Magnetosphere which flows from the Magnetotail towards the Earth on the dawn side

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. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the The heliospheric current sheet (HCS is the surface within the Solar System where the polarity of the Sun 's Magnetic field changes from 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 . "^[22]

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. Critical ionization velocity (CIV also called Critical velocity, CV is the relative velocity between a neutral Gas and plasma (an ionized gas at which 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.

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. Detailed list of temperatures from 100 K to 1000 K Most ordinary human activity takes place at temperatures of this order of magnitude 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.

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. 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. A particle beam is an accelerated stream of Charged particles or Neutrons (often moving at very near the Speed of light) which may be directed by Magnets Penning traps are devices for the storage of charged particles using a constant static Magnetic field and a spatially inhomogeneous static Electric field. ^[23]

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 dusty plasma is a plasma containing nanometer or micrometer-sized particles suspended in it A plasma containing larger particles is called a grain plasma.

Mathematical descriptions

The complex self-constricting magnetic field lines and current paths in a field-aligned Birkeland current which may develop in a plasma^[24]

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. A Birkeland current is a specific magnetic field aligned current in the Earth’s Magnetosphere which flows from the Magnetotail towards the Earth on the dawn side Plasma Modeling refers to solving Equations of motion that describe the state of a plasma. 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:

Fluid model

Fluid models describe plasmas in terms of smoothed quantities like density and averaged velocity around each position (see Plasma parameters). Plasma parameters define various characteristics of a plasma, an electrically conductive collection of Charged particles that responds collectively 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. Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric The Navier–Stokes equations, named after Claude-Louis Navier and George Gabriel Stokes, describe the motion of viscous Fluid substances such 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. The Maxwell–Boltzmann distribution is a Probability distribution with applications in Physics and Chemistry. 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.

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. The Maxwell–Boltzmann distribution is a Probability distribution with applications in Physics and Chemistry. 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. The Particle-in-Cell ( PIC) method refers to a technique used to solve a certain class of Partial differential equations. 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 Boltzmann equation, also often known as the Boltzmann transport equation, devised by Ludwig Boltzmann, describes the statistical distribution of

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 = T_ion = T_gas), Non-Thermal or "cold" plasma (Te >> T_ion = T_gas)
• 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). The gyroradius (also known as radius of gyration, Larmor radius or cyclotron radius) defines the Radius of the circular motion of a Charged
• Its application

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. Electric glow discharge is a type of plasma formed by passing a current at 100 V to several kV through a gas usually Argon or another Noble Probably the most common plasma; this is the type of plasma generated within fluorescent light tubes. A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor.
• Capacitively coupled plasma (CCP): similar to glow discharge plasmas, but generated with high frequency RF electric fields, typically 13. A capacitively coupled plasma (CCP is one of the most common types of industrial Plasma sources It essentially consists of two metal Electrodes separated by a small 56 MHz. These differ 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 plasma (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. An inductively coupled plasma ( ICP) is a type of plasma source in which the Energy is supplied by Electrical currents which are produced by
• Wave heated plasma: similar to CCP and ICP in that it is typically RF (or microwave), but is heated by both electrostatic and electromagnetic means. Examples are helicon discharge, electron cyclotron resonance (ECR), and ion cyclotron resonance (ICR). A helicon is a low frequency Electromagnetic wave. Helicons have the special ability to propagate through pure metals given conditions of low temperature and high magnetic Electron cyclotron resonance is a phenomenon observed both in Plasma physics and Condensed matter physics. Ion cyclotron resonance is a phenomenon related to the movement of Ions in a Magnetic field. These typically require a coaxial magnetic field for wave propagation.

Atmospheric pressure

• Arc discharge: this is a high power thermal discharge of very high temperature ~10,000 K. An electric arc is an Electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive It can be generated using various power supplies. It is commonly used in metallurgical processes. Metallurgy is a domain of Materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their For example it is used to melt rocks containing Al₂O₃ to produce aluminium. WikipediaNaming
• Corona discharge: this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. In Electricity, a corona discharge is an Electrical discharge brought on by the Ionization of a Fluid surrounding a conductor, which It is commonly used in ozone generators and particle precipitators. OZONE is an object oriented Operating system written in the C programming language.
• Dielectric barrier discharge (DBD): 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. Dielectric-barrier discharge (DBD is the Electrical discharge between two Electrodes separated by an insulating Dielectric barrier 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.

Fields of active research

Hall effect thruster. In Spacecraft propulsion, a Hall thruster is a type of Ion thruster in which the Propellant is accelerated by an electric field 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. An ion thruster is a form of Electric propulsion used for Spacecraft propulsion that creates thrust by accelerating Ions Ion thrusters are characterized A more complete and organized list can be found on the Web site for Plasma science and technology. ^[25]

Footnotes

See also

• Plasma channel
• Plasma parameters
• Magnetohydrodynamics
• Electric field screening
• List of plasma physicists
• Important publications in plasma physics
• IEEE Nuclear and Plasma Sciences Society

External links

• Plasmas: the Fourth State of Matter
• Animation on the plasma excitation
• Plasma Science and Technology
• Plasma on the Internet comprehensive list of plasma related links. A plasma channel is a conductive channel of plasma. A plasma channel can be formed in these ways- With a high-powered Laser that operates at a certain Plasma parameters define various characteristics of a plasma, an electrically conductive collection of Charged particles that responds collectively Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically Screening is the damping of Electric fields caused by the presence of mobile charge carriers Alexei Alexeyevich Abrikosov Hannes Alfvén - Received the only Nobel Prize specifically for contributions to plasma physics Optics Book of Optics The IEEE Nuclear and Plasma Sciences Society (NPSS is a transnational group of about 3000 professional engineers and scientists
• Introduction to Plasma Physics: Graduate course given by Richard Fitzpatrick | M.I.T. Introduction by I.H.Hutchinson
• NRL Plasma Formulary online (or an html version)
• Plasma Coalition page
• Plasma Material Interaction
• How to make a glowing ball of plasma in your microwave with a grape | More (Video)
• How to make plasma in your microwave with only one match (video)

• U. S. Dept of Agriculture research project "Decontamination of Fresh Produce with Cold Plasma"
• CNRS LAEPT "Electric Arc Thermal Plasmas (french)