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plasma physics Plasma ()πλάσμα
, Henry George Liddell, R ...
, waves in plasmas are an interconnected set of particles and fields which propagate in a periodically repeating fashion. A plasma is a quasineutral,
electrically conductive Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
. In the simplest case, it is composed of
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kno ...
s and a single species of positive
ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conv ...
s, but it may also contain multiple ion species including negative ions as well as neutral particles. Due to its
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
, a plasma couples to
electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
and
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
s. This complex of particles and fields supports a wide variety of
wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (re ...
phenomena. The electromagnetic fields in a plasma are assumed to have two parts, one static/equilibrium part and one oscillating/perturbation part. Waves in plasmas can be classified as electromagnetic or electrostatic according to whether or not there is an oscillating magnetic field. Applying
Faraday's law of induction Faraday's law of induction (briefly, Faraday's law) is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (emf)—a phenomenon known as electromagnetic inducti ...
to
plane wave In physics, a plane wave is a special case of wave or field: a physical quantity whose value, at any moment, is constant through any plane that is perpendicular to a fixed direction in space. For any position \vec x in space and any time t, th ...
s, we find \mathbf\times\tilde=\omega\tilde, implying that an electrostatic wave must be purely
longitudinal Longitudinal is a geometric term of location which may refer to: * Longitude ** Line of longitude, also called a meridian * Longitudinal engine, an internal combustion engine in which the crankshaft is oriented along the long axis of the vehicle, ...
. An electromagnetic wave, in contrast, must have a
transverse Transverse may refer to: *Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle *Transverse flute, a flute that is held horizontally * Transverse force (or ''Euler force''), the tangen ...
component, but may also be partially longitudinal. Waves can be further classified by the oscillating species. In most plasmas of interest, the
electron temperature Plasma parameters define various characteristics of a plasma, an electrically conductive collection of charged particles that responds ''collectively'' to electromagnetic forces. Plasma typically takes the form of neutral gas-like clouds or char ...
is comparable to or larger than the ion temperature. This fact, coupled with the much smaller mass of the electron, implies that the electrons move much faster than the ions. An electron mode depends on the mass of the electrons, but the ions may be assumed to be infinitely massive, i.e. stationary. An ion mode depends on the ion mass, but the electrons are assumed to be massless and to redistribute themselves instantaneously according to the
Boltzmann relation In a plasma, the Boltzmann relation describes the number density of an isothermal charged particle fluid when the thermal and the electrostatic forces acting on the fluid have reached equilibrium. In many situations, the electron density of a ...
. Only rarely, e.g. in the
lower hybrid oscillation In plasma physics, a lower hybrid oscillation is a longitudinal oscillation of ions and electrons in a magnetized plasma. The direction of propagation must be very nearly perpendicular to the stationary magnetic field, within about radians. Other ...
, will a mode depend on both the electron and the ion mass. The various modes can also be classified according to whether they propagate in an unmagnetized plasma or parallel, perpendicular, or oblique to the stationary magnetic field. Finally, for perpendicular electromagnetic electron waves, the perturbed electric field can be parallel or perpendicular to the stationary magnetic field. {, class="wikitable" , + Summary of elementary plasma waves , - ! EM character !! oscillating species !! conditions !! dispersion relation !! name , - , rowspan = 5 , electrostatic , , rowspan = 2 , electrons , , \vec B_0=0\ {\rm or}\ \vec k\, \vec B_0 , , \omega^2=\omega_p^2+3k^2v_{th}^2 , ,
plasma oscillation Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability i ...
(or Langmuir wave) , - , \vec k\perp\vec B_0 , , \omega^2=\omega_p^2+\omega_c^2=\omega_h^2 , ,
upper hybrid oscillation In plasma physics, an upper hybrid oscillation is a mode of oscillation of a magnetized plasma. It consists of a longitudinal motion of the electrons perpendicular to the magnetic field with the dispersion relation : \omega^2 = \omega_^2 + \omeg ...
, - , rowspan = 3 , ions , , \vec B_0=0\ {\rm or}\ \vec k\, \vec B_0 , , \omega^2=k^2v_s^2=k^2\frac{\gamma_eKT_e+\gamma_iKT_i}{M} , ,
ion acoustic wave In plasma physics, an ion acoustic wave is one type of longitudinal oscillation of the ions and electrons in a plasma, much like acoustic waves traveling in neutral gas. However, because the waves propagate through positively charged ions, ion aco ...
, - , \vec k\perp\vec B_0 (nearly), , \omega^2=\Omega_c^2+k^2v_s^2 , ,
electrostatic ion cyclotron wave In plasma physics, an electrostatic ion cyclotron wave is a longitudinal oscillation of the ions (and electrons) in a magnetized plasma, propagating nearly (but not exactly) perpendicular to the magnetic field. The angle (in radians) between the di ...
, - , \vec k\perp\vec B_0 (exactly), , \omega^2= \Omega_c\omega_c)^{-1}+\omega_i^{-2}{-1} , ,
lower hybrid oscillation In plasma physics, a lower hybrid oscillation is a longitudinal oscillation of ions and electrons in a magnetized plasma. The direction of propagation must be very nearly perpendicular to the stationary magnetic field, within about radians. Other ...
, - , rowspan = 8 , electromagnetic , , rowspan = 5 , electrons , , \vec B_0=0 , , \omega^2=\omega_p^2+k^2c^2 , ,
light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahe ...
wave , - , \vec k\perp\vec B_0,\ \vec E_1\, \vec B_0 , , \frac{c^2k^2}{\omega^2}=1-\frac{\omega_p^2}{\omega^2} , , O wave , - , \vec k\perp\vec B_0,\ \vec E_1\perp\vec B_0 , , \frac{c^2k^2}{\omega^2}=1-\frac{\omega_p^2}{\omega^2}\, \frac{\omega^2-\omega_p^2}{\omega^2-\omega_h^2} , , X wave , - , \vec k\, \vec B_0 ( right circ. pol.), , \frac{c^2k^2}{\omega^2}=1-\frac{\omega_p^2/\omega^2}{1-(\omega_c/\omega)} , ,
R wave The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the ri ...
(whistler mode) , - , \vec k\, \vec B_0 ( left circ. pol.), , \frac{c^2k^2}{\omega^2}=1-\frac{\omega_p^2/\omega^2}{1+(\omega_c/\omega)} , , L wave , - , rowspan = 3 , ions , , \vec B_0=0 , ,   , , none , - , \vec k\, \vec B_0 , , \omega^2=k^2v_A^2 , ,
Alfvén wave In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of plasma wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines. Definition An Alfvén wave is a ...
, - , \vec k\perp\vec B_0 , , \frac{\omega^2}{k^2}=c^2\, \frac{v_s^2+v_A^2}{c^2+v_A^2} , ,
magnetosonic wave A magnetosonic wave, also called a magnetoacoustic wave, is a linear magnetohydrodynamic (MHD) wave that is driven by thermal pressure, magnetic pressure, and magnetic tension. There are two types of magnetosonic waves, the ''fast'' magnetosonic ...
\omega - wave frequency, k -
wave number In the physical sciences, the wavenumber (also wave number or repetency) is the ''spatial frequency'' of a wave, measured in cycles per unit distance (ordinary wavenumber) or radians per unit distance (angular wavenumber). It is analogous to temp ...
, c -
speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit for ...
, \omega_p -
plasma frequency Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability i ...
, \omega_i - ion
plasma frequency Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability i ...
, \omega_c - electron gyrofrequency, \Omega_c - proton gyrofrequency, \omega_h - upper hybrid frequency, v_s - plasma "sound" speed, v_A - plasma Alfvén speed (The subscript 0 denotes the static part of the electric or magnetic field, and the subscript 1 denotes the oscillating part.)


Bibliography

*Swanson, D.G. ''Plasma Waves'' (2003). 2nd edition. * Stix, Thomas Howard.
Waves in Plasmas
' (1992). *Chen, Francis F. ''Introduction to Plasma Physics and Controlled Fusion'', 2nd edition (1984).


See also

* Magnetohydrodynamic waves * Appleton-Hartree equation *
Plasmon In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantiz ...
*
Surface plasmon resonance Surface plasmon resonance (SPR) is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material in a particle stimulated by incident light. SPR is the basis of many standard tools for measu ...
*
Index of wave articles This is a list of Wave topics. 0–9 * 21 cm line A * Abbe prism *Absorption spectroscopy *Absorption spectrum *Absorption wavemeter *Acoustic wave *Acoustic wave equation *Acoustics *Acousto-optic effect *Acousto-optic modulator *Acoust ...
*
List of plasma physics articles This is a list of plasma physics topics. A * Ablation * Abradable coating * Abraham–Lorentz force * Absorption band * Accretion disk * Active galactic nucleus * Adiabatic invariant * ADITYA (tokamak) * Aeronomy * Afterglow plasma * Airgl ...
*
Waves (Juno) Waves is an experiment on the '' Juno'' spacecraft to study radio and plasma waves. It is part of collection of various types of instruments and experiments on the spacecraft; Waves is oriented towards understanding fields and particles i ...
(spacecraft instrument aboard Jupiter orbiter) * Plasma Wave Subsystem (Instrument on Voyager probes)