NationMaster - Encyclopedia: Plasma oscillation

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. The particle resulting from the quantization of these oscillations is the plasmon. A Plasma lamp In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. ... Irving Langmuir (January 31, 1881 in Brooklyn, New York - August 16, 1957 in Woods Hole, Massachusetts) was an American chemist and physicist. ... Charge density is the amount of electric charge per unit volume. ... For other uses, see Plasma. ... This article is about metallic materials. ... For the novel, see The Elementary Particles. ... In physics, quantization is a procedure for constructing a quantum field theory starting from a classical field theory. ... In physics, the plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves, respectively. ...

1 Explanation
- 1.1 'Cold' electrons
- 1.2 'Warm' electrons
2 Langmuir waves
3 See also
4 References

Explanation

Consider a neutral plasma, consisting of a gas of positively charged ions and negatively charged electrons. If one displaces by a tiny amount all of the electrons with respect to the ions, the Coulomb force pulls back, acting as a restoring force. This article is about the electrically charged particle. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrical force that one stationary, electrically charged substance of small volume (ideally, a point source) exerts on another. ...

'Cold' electrons

If the electrons are cold, it is possible to show that the charge density oscillates at the plasma frequency

$omega_{pe} = sqrt{frac{4 pi n_e e^{2}}{m}}$ (cgs units) $= sqrt{frac{n_e e^{2}}{mepsilon_0}}$ (SI units) $= (56.4,mathrm{rad/s})times(n/mathrm{m^{-3}})$ ,

where $n e$ is the density of electrons, e is the electric charge, m is the mass of the electron, and $ε 0$ is the permittivity of free space. Note that the above formula is derived under the approximation that the ion mass is infinite. This is generally a good approximation, as the electrons are so much lighter than ions. (One must modify this expression in the case of electron-positron plasmas, often encountered in astrophysics). Since the frequency is independent of the wavelength, these oscillations have an infinite phase velocity and zero group velocity. This article or section is in need of attention from an expert on the subject. ... The International System of Units (symbol: SI) (for the French phrase Système International dUnités) is the most widely used system of units. ... This article is in need of attention. ... In mathematics and in the sciences, a formula (plural: formulae, formulÃ¦ or formulas) is a concise way of expressing information symbolically (as in a mathematical or chemical formula), or a general relationship between quantities. ... It has been suggested that this article or section be merged with estimation. ... The first detection of the positron in 1932 by Carl D. Anderson The positron is the antiparticle or the antimatter counterpart of the electron. ... 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 celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... For other uses, see Frequency (disambiguation). ... For other uses, see Wavelength (disambiguation). ... Oscillation is the variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. ... Infinity is a word carrying a number of different meanings in mathematics, philosophy, theology and everyday life. ... The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ... The group velocity of a wave is the velocity with which the variations in the shape of the waves amplitude (known as the modulation or envelope of the wave) propagate through space. ...

'Warm' electrons

If warm electrons are considered with an electron thermal speed v_e,th = (k_BT_e)^3/2, the electron pressure acts as a restoring force as well as the electric field and the oscillations propagate with frequency and wavenumber related by For other uses, see Electron (disambiguation). ... Wavenumber in most physical sciences is a wave property inversely related to wavelength, having SI units of reciprocal meters (mâˆ’1). ...

$omega^2 = omega_{pe}^2 + 3 k^2 v_{mathrm{e,th}}^2$ ,

called the Bohm-Gross dispersion relation. If the spatial scale is large compared to the Debye length, the oscillations are only weakly modified by the pressure term, but at small scales the pressure term dominates and the waves become dispersionless with a speed of 3^1/3v_e,th. For such waves, however, the electron thermal speed is comparable to the phase velocity, i.e., David Bohm. ... The relation between the energy of a system and its corresponding momentum is known as its dispersion relation. ... In plasma physics, the Debye length, named after the Dutch physical chemist Peter Debye, is the scale over which mobile charge carriers (e. ... Oscillation is the variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. ... This article is about pressure in the physical sciences. ... The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ...

$v sim v_{ph} stackrel{mathrm{def}}{=} frac{omega}{k},$

so the plasma waves can accelerate electrons that are moving with speed nearly equal to the phase velocity of the wave. This process often leads to a form of collisionless damping, called Landau damping. Consequently, the large-k portion in the dispersion relation is difficult to observe and seldom of consequence. Acceleration is the time rate of change of velocity, and at any point on a v_t graph, it is given by the gradient of the tangent to that point In physics, acceleration (symbol: a) is defined as the rate of change (or time derivative) of velocity. ... In physics, Landau damping, named after its discoverer, the eminent Russian physicist Lev Davidovich Landau, is the effect of damping (exponential decrease as a function of time) of longitudinal space charge waves in plasma or a similar environment. ... The relation between the energy of a system and its corresponding momentum is known as its dispersion relation. ...

In a bounded plasma, fringing electric fields can result in propagation of plasma oscillations, even when the electrons are cold. The term bounded appears in different parts of mathematics where a notion of size can be given. ...

In a metal or semiconductor, the effect of the ions' periodic potential must be taken into account. This is usually done by using the electrons' effective mass in place of m. This article is about metallic materials. ... A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... This article is about the electrically charged particle. ... In solid state physics, a particles effective mass is the mass it seems to carry in the semiclassical model of transport in a crystal. ...

Langmuir waves

Langmuir waves are longitudinal plasma oscillations.

In waves of the form $Delta=Delta_0 e^{i(mathbf{kcdot r}-omega t)}$ , Langmuir waves are governed by $omega^2=c_s^2k^2+frac{n_e e^2}{m_e epsilon_0}$ where $n e$ is electron density and $m e$ is the electron mass. A WAVES Photographer 3rd Class The WAVES were a World War II era division of the U.S. Navy that consisted entirely of women. ... For other uses, see Electron (disambiguation). ...

Langmuir waves were discovered by American physicists Irving Langmuir and Lewi Tonks in the 1920s. They are parallel in form to Jeans instability waves, which are caused by gravitational instabilities in a static medium. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Irving Langmuir (January 31, 1881 in Brooklyn, New York - August 16, 1957 in Woods Hole, Massachusetts) was an American chemist and physicist. ... Lewi Tonks, 1897-1971, American quantum physicist noted for discovery (with Marvin D. Girardeau) of the Tonks-Girardeau gas. ... The 1920s is sometimes referred to as the Jazz Age or the Roaring Twenties, usually applied to America. ... It has been suggested that Jeans mass be merged into this article or section. ...

In 2006, plasma physicists at the Universities of Texas and Michigan were able to photograph Langmuir waves, generated by a 30 TW laser pulse, for the first time.^[1]

References

Longair, Malcolm S., "Galaxy Formation", 1998.

^ Fastest waves ever photographed

Categories: Waves in plasmas | Plasma physics

Results from FactBites:

Plasma oscillation - Wikipedia, the free encyclopedia (499 words)
	In a bounded plasma, fringing electric fields can result in propagation of plasma oscillations, even when the electrons are cold.
	In 2006, plasma physicists at the Universities of Texas and Michigan were able to photograph Langmuir waves, generated by a 30 TW laser pulse, for the first time.
	Upper hybrid oscillation, in particular for a discussion of the modification to the mode at propagation angles oblique to the magnetic field

PowerPedia:Plasma - PESWiki (4601 words)
	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).
	The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics.
	A nonthermal plasma is in general any plasma which is not in thermodynamic equilibrium, either because the ion temperature is different from the electron temperature, or because the velocity distribution of one of the species does not follow a Maxwell-Boltzmann distribution.

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Contents

Explanation GA_googleFillSlot("encyclopedia_square");

'Cold' electrons

'Warm' electrons

Langmuir waves

See also

References

Explanation