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
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  The nature of the Crookes tube "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897, and dubbed "plasma" by Irving Langmuir in 1928, 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  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. "
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  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
|Common forms of plasma include|
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:
|Typical ranges of plasma parameters: orders of magnitude (OOM)|
|Characteristic||Terrestrial plasmas||Cosmic plasmas|
|10−6 m (lab plasmas) to|
102 m (lightning) (~8 OOM)
|10−6 m (spacecraft sheath) to|
1025 m (intergalactic nebula) (~31 OOM)
|10−12 s (laser-produced plasma) to|
107 s (fluorescent lights) (~19 OOM)
|101 s (solar flares) to|
1017 s (intergalactic plasma) (~17 OOM)
in particles per
|107 m-3 to|
1032 m-3 (inertial confinement plasma)
|100 (i. 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 e. , 1) m-3 (intergalactic medium) to|
1030 m-3 (stellar core)
|~0 K (crystalline non-neutral plasma) to|
108 K (magnetic fusion plasma)
|102 K (aurora) to|
107 K (solar core)
|10−4 T (lab plasma) to|
103 T (pulsed-power plasma)
|10−12 T (intergalactic medium) to|
1011 T (near neutron stars)
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 = 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.
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.
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":
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
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. 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 
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:
|Electrical Conductivity||Very low||Usually very high|
|Independently acting species||One||Two or three|
|Velocity distribution||Maxwellian||Often non-Maxwellian|
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:
The striations or "stringy" things, seen in many plasmas, like the plasma ball (image above), the aurora, lightning, electric arcs, solar flares, and supernova remnants 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.  (See also Plasma pinch)
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.
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
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 . "
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.
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
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. 
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.
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 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 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
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:
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.