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Solar Wind

Solar wind

meeting the heliopause]] :Ion storm redirects here. For information about the games software company, see Ion Storm Inc. For the British comic, see Solar Wind (comic). A solar wind is a stream of charged particles (i.e., a plasma) which are ejected from the upper atmosphere of a star. When originating from stars other than the Earth's Sun, it is sometimes called a stellar wind. It consists mostly of high-energy electrons and protons (about 500 keV) that are able to escape the star's gravity because of their high thermal energy. Many phenomena can be explained by the solar wind, including: geomagnetic storms that knock out power grids on Earth, auroras, why the tail of a comet always points away from the Sun, and the formation of distant stars.

History

comet, a magnetised anode globe in an evacuated chamber.]] In 1916, Norwegian researcher Kristian Birkeland was probably the first person to successfully predict that in the Solar Wind, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds"; in other words, the Solar Wind consists of both negative electrons and positive ions. Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun. Around the 1930s, scientists had determined that the temperature of the solar corona must be a million degrees Celsius because of the way it stood out into space (as seen during total eclipses). Some very clever spectroscopic detective work confirmed this extraordinary temperature. In the mid-1950s the British mathematician Sydney Chapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, a German scientist named Ludwig Biermann became interested in the fact that no matter whether a comet is headed towards or away from the Sun, its tail always points away from the Sun. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away. Eugene Parker realised that the heat flowing from the Sun in Chapman's model and the comet tail blowing away from the Sun in Biermann's hypothesis had to be the result of the same phenomenon. Parker showed that even though the Sun's corona is strongly attracted by solar gravity, it is such a good conductor of heat that it is still very hot at large distances. Since gravity weakens as distance from the Sun increases, the outer coronal atmosphere escapes into interstellar space. Opposition to Parker's hypothesis on the solar wind was strong. The paper he submitted to the Astrophysical Journal in 1958 was rejected by two reviewers. It was saved by the editor Subrahmanyan Chandrasekhar (who later received the 1983 Nobel Prize in physics). In January 1959, the first ever direct observations and measurements of strength of the solar wind were made by the Soviet satellite Luna 1. However, the acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. In the late 1990s the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the Sun, and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about 4 solar radii from the photosphere; but the transition (or "sonic point") now appears to be much lower, perhaps only 1 solar radius above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the Sun.

Properties

In the solar system, the composition of the solar wind is identical to the Sun's corona: 73% ionized hydrogen and 25% ionized helium with the remainder as trace impurities. These components are present as a plasma, consisting of about 95% singly ionized hydrogen, 4% doubly ionized helium, and less than 0.5% other ions (often called minor ions). The exact composition has been difficult to measure due to large fluctuations. A sample return mission, Genesis, returned to Earth in 2004 and is undergoing analysis, but it was damaged by crash-landing when its parachute failed to deploy on re-entry to Earth's atmosphere, possibly contaminating the solar samples. Near Earth, the velocity of the solar wind varies from 200 to 889 km/s. The average is 450 km/s. Approximately 1×10⁹ kg/s [http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v574n1/55336/55336.html] of material is lost by the Sun as ejected solar wind, about one-fifth that lost due to fusion, which is equivalent to about 4.5 Tg (4.5×10⁹ kg) of mass converted to energy every second. The total mass loss is equivalent to a lump of Earth-density rock about 125 m across every second, and at that rate the Sun would last for 10 million million (1×10¹³) years. However, our current understanding of star formation implies that the Sun's solar wind may have been about 1000 times more massive in the distant past, which would seriously affect the history of planetary atmospheres and that of the martian atmosphere in particular. martian's rotating magnetic field on the plasma in the interplanetary medium (Solar Wind) [http://quake.stanford.edu/~wso/gifs/HCS.html]. (click to enlarge) ]] Since the solar wind is a plasma, it has the characteristics of a plasma, rather than a simple gas. For example, it is highly electrically conductive so that magnetic field lines from the Sun are carried along with the wind. The dynamic pressure of the wind dominates over the magnetic pressure through most of the solar system (or heliosphere), so that the magetic field is pulled into an Archimedean spiral pattern (the Parker spiral) by the combination of the outward motion and the Sun's rotation. Depending on the hemisphere and phase of the solar cycle, the magnetic field spirals inward or outward; the magnetic field follows the same shape of spiral in the northern and southern parts of the heliosphere, but with opposite field direction. These two magnetic domains are separated by a two current sheet (an electric current that is confined to a curved plane). This heliospheric current sheet has a similar shape to a twirled ballerina skirt, and changes in shape through the solar cycle as the Sun's magnetic field reverses about every 11 years. The plasma in the interplanetary medium is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's 10^-4 tesla magnetic dipole field would reduce with the cube of the distance to about 10^-11 tesla. But satellite observations show that it is about 100 times greater at around 10^-9 tesla. Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g. the interplanetary medium) in a magnetic field, induces electric currents which in turn generates magnetic fields, and in this respect it behaves like a MHD dynamo.

Fast and slow solar wind

Outside the plane of the ecliptic the solar wind is steady and rapid, at speeds between 600-800 km/s; this is called the fast solar wind and it is known to emanate from solar coronal holes. In the plane of the ecliptic, near the heliospheric current sheet, the wind is slower, denser, and more variable, with typical speeds between 200 and 600 km/s and daily fluctuations by a factor of two or more. This is called the slow solar wind and its location of origin on the Sun is less well known.

Variability and space weather

The solar wind is responsible for the overall shape of Earth's magnetosphere, and fluctuations in its speed, density, direction, and entrained magnetic field strongly affect Earth's local space environment. For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the geopause (Earth's bow shock wave in the solar wind) can change by several Earth radii, exposing geosynchronous satellites to the direrct solar wind. These phenomena are collectively called space weather. Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called interplanetary coronal mass ejections, or ICMEs. ICMEs are the interplanetary manifestation of solar coronal mass ejections, which are caused by release of magnetic energy at the Sun. ICMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. ICMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation) that precede the ICME. When an ICME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a magnetic storm and it is a global phenomenon. ICME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora. ICMES are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Faster-moving streams tend to overtake slower streams that originate westward of them on the Sun, forming turbulent corotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, ICMEs.

Outer limits

The solar wind blows a "bubble" in the interstellar medium (the rarefied hydrogen and helium gas that permeates the galaxy). The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause, and is often considered to be the outer "border" of the solar system. The distance to the heliopause is not precisely known, and probably varies widely depending on the current velocity of the solar wind and the local density of the interstellar medium, but it is known to lie far outside the orbit of Pluto.

References

- http://news.nationalgeographic.com/news/2003/08/0827_030827_kyotoprizeparker.html

Notes

- Kristian Birkeland, "Are the Solar Corpuscular Rays that penetrate the Earth's Atmosphere Negative or Positive Rays?" in Videnskapsselskapets Skrifter, I Mat -- Naturv. Klasse No.1, Christiania, 1916.
- Philosophical Magazine, Series 6, Vol. 38, No. 228, December, 1919, 674 (on the Solar Wind)

Ion Storm Inc.

:This is an article about the games software company. For information about the astronomical phenomenon, see Ion storm. Ion storm Ion Storm Inc. (sometimes spelled ION Storm) was a Texas based developer of computer games that was founded by John Romero, Tom Hall, Jerry O'Flaherty and Todd Porter in Dallas on November 15, 1996. The company was divided into two branches; the main office in Dallas, and another office in Austin. The expensive Dallas office sat on the 54th and top floor of the Chase Tower and produced two games which had been heavily hyped over their long development: Anachronox and Daikatana as well as Dominion which was quietly released before either of them. Anachronox received critical acclaim for its vast storyline and characters while Daikatana was critically savaged as a below-average 3D shooter. Both games were commercially unsuccessful. Romero in particular, who headed the Dallas offices, was widely criticised for the extravagance of the operation compared to the eventual output. The Austin branch, however, was more successful — under Warren Spector, it developed the highly successful and critically acclaimed Deus Ex with a staff gathered in part of ex-Looking Glass Studios employees. Romero and Hall left the company after producing Anachronox in July 2001. A grand total of 4 games had been released in 4.5 years of the company's existence. Later that year, Eidos Interactive, owner of Ion Storm, closed the Dallas offices. The Austin office remained open, led by Spector, moving on to produce Deus Ex: Invisible War and Thief: Deadly Shadows until his departure to "pursue personal interests outside the company" in 2004. A number of other senior staff also left at about the same time. On February 9, 2005, Eidos announced that the Austin office would also close, meaning the end of Ion Storm as a company.

Games by Ion Storm

- Dominion: Storm Over Gift 3 — (1998) (PC), produced by the Dallas branch, led by Todd Porter.
- Daikatana — (2000) (PC, Nintendo 64, Game Boy Color), produced by the Dallas branch, led by John Romero.
- Deus Ex — (2000) (PC, PlayStation 2), produced by the Austin branch.
- Anachronox — (2001) (PC), produced by the Dallas branch, led by Tom Hall.
- Deus Ex: Invisible War — (2003) (PC, Xbox), produced by the Austin branch.
- Thief: Deadly Shadows — (2004) (PC, Xbox), produced by the Austin branch.

External links

- [http://www.mobygames.com/browse/games/ion-storm-inc/ Ion Storm entry] at MobyGames
- [http://www.salon.com/tech/feature/2002/01/02/ion_storm/index.html?x Salon article on Ion Storm] Category:Defunct computer and video game companies

Solar Wind (comic)

Solar Wind is a British small press comicbook. Edited by Cosmic Ray (a pseudonym for small press comics publisher Paul Von Scott), the comic is devoted to gentle parodies of British boys' comics of the 1970's and 80's. Emerging originally from the fanbase of best selling British comic 2000AD, Solar Wind has featured writers and artists including Frazer Irving, Gordon Rennie, Rufus Dayglo, Al Ewing and PJ Holden.

Reviews

Don't let anyone tell you different: Solar Wind is the funniest comic of the decade. - Comics International #161

Awards

In 2004, the title won the Best Independent Comic Award at the British Diamond Comics Awards.

Spin-offs

Solar Wind has two direct spin-off publications - Big War Comic and Sunny For Girls. The same small-press publisher also produces Omnivistascope comics. It has proved an inspiration for a group of other fanzines, including FutureQuake, Pony School and The End Is Nigh.

External links

[http://www.solarwindcomic.co.uk/index.html Solar Wind homepage] Category:British comics Category:British small press comics Category:Comic book magazines

Plasma

:This article is about plasma in the sense of an ionized gas. For other uses of the term, such as blood plasma, see plasma (disambiguation). plasma (disambiguation) In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. "Ionized" in this case means that at least one electron has been removed from a significant fraction of the molecules. The free electric charges make the plasma electrically conductive so that it couples strongly to electromagnetic fields. This fourth state of matter was first identified by Sir William Crookes in 1879 and dubbed "plasma" by Irving Langmuir in 1928, because it reminded him of a blood plasma [http://www.plasmacoalition.org/what.htm].

Common plasmas

blood plasma Plasmas are the most common phase of matter. The entire visible universe outside the Solar System is plasma, since all we can see are stars. Since the space between the stars is filled with a plasma, although a very sparse one (see interstellar- and intergalactic medium), essentially the entire volume of the universe is plasma. 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. Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of a plasma (see dusty plasmas). Commonly encountered forms of plasma include:
- Artificially produced
- Inside fluorescent lamps (low energy lighting), neon signs
- Rocket exhaust
- The area in front of a spacecraft's heat shield during reentry into the atmosphere
- Fusion energy research
- The electric arc in an arc lamp or an arc welder
- Plasma ball (sometimes called a plasma sphere or plasma globe)
- Earth plasmas
- Flames (ie. fire)
- Lightning
- The ionosphere
- The polar aurorae
- Space and astrophysical
- The Sun and other stars (which are plasmas heated by nuclear fusion)
- The solar wind
- The Interplanetary medium (the space between the planets)
- The Interstellar medium (the space between star systems)
- The Intergalactic medium (the space between galaxies)
- The Io-Jupiter flux-tube
- Accretion disks
- Interstellar nebulae

Characteristics

The term plasma is generally reserved for a system of charged particles large enough to behave as one. 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). In technical terms, the typical characteristics of a plasma are: # Debye screening lengths that are short compared to the physical size of the plasma. # Large number of particles within a sphere with a radius of the Debye length. # Mean time between collisions usually is long when compared to the period of plasma oscillations.

Plasma scaling

Plasmas and their characteristics exist over a wide range of scales (ie. they are scaleable over many orders of magnitude). The following chart deals only with conventional atomic plasmas and not other exotic phenomena, such as, quark gluon plasmas:

	Typical plasma scaling ranges: orders of magnitude (OOM)
Characteristic	Terrestrial plasmas	Cosmic plasmas
Size in metres (m)	10⁻⁶ m (lab plasmas) to: 10² m (lightning) (~8 OOM)	10⁻⁶ m (spacecraft sheath) to 10²⁵ m (intergalactic nebula) (~31 OOM)
Lifetime in seconds (s)	10⁻¹² s (laser-produced plasma) to: 10⁷ s (fluorescent lights) (~19 OOM)	10¹ s (solar flares) to: 10¹⁷ s (intergalactic plasma) (~17 OOM)
Density in particles per cubic metre	10⁷ to: 10²¹ (inertial confinement plasma)	10³⁰ (stellar core) to: 10⁰ (i.e., 1) (intergalactic medium)
Temperature in kelvins (K)	~0 K (Crystalline non-neutral plasma[http://sdphca.ucsd.edu/]) to: 10⁸ K (magnetic fusion plasma)	10² K (aurora) to: 10⁷ K (Solar core)
Magnetic fields in teslas (T)	10⁻⁴ T (Lab plasma) to: 10³ T (pulsed-power plasma)	10⁻¹² T (intergalactic medium) to: 10⁷ T (Solar core)

Temperatures

plasma scaling characteristic of the gas being excited.]] The defining characteristic of a plasma is ionization. Although ionization can be caused by UV radiation, energetic particles, or strong electric fields, (processes that tend to result in a non-Maxwellian electron distribution function), it is more commonly caused by heating the electrons in such a way that they are close to thermal equilibrium so the electron temperature is relatively well-defined. Because the large mass of the ions relative to the electrons hinders energy transfer, it is possible for the ion temperature to be very different from (usually lower than) the electron temperature. The degree of ionization is determined by the electron temperature relative to the ionization energy (and more weakly by the density) in accordance with the Saha equation. If only a small fraction of the gas molecules are ionized (for example 1%), then the plasma is said to be a cold plasma, even though the electron temperature is typically several thousand degrees. The ion temperature in a cold plasma is often near the ambient temperature. Because the plasmas utilized in plasma technology are typically cold, they are sometimes called technological plasmas. They are often created by using a very high electric field to accelerate electrons, which then ionize the atoms. The electric field is either capacitively or inductively coupled into the gas by means of a plasma source, e.g. microwaves. Common applications of cold plasmas include plasma-enhanced chemical vapor deposition, plasma ion doping, and reactive ion etching. A hot plasma, on the other hand, is nearly fully ionized. This is what would commonly be known as the "fourth-state of matter". The Sun is an example of a hot plasma. The electrons and ions are more likely to have equal temperatures in a hot plasma, but there can still be significant differences.

Densities

Next to the temperature, which is of fundamental importance for the very existence of a plasma, the most important property is the density. The word "plasma density" by itself usually refers to the electron density, that is, the number of free electrons per unit volume. The ion density is related to this by the average charge state

\langle Z\rangle

of the ions through

n_e=\langle Z\rangle n_i

. (See quasineutrality below.) The third important quantity is the density of neutrals

n_0

. In a hot plasma this is small, but may still determine important physics. The degree of ionization is

n_i/(n_0+n_i)

Potentials

reactive ion etching 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 the development of a Debye sheath. Due to the good electrical conductivity, the electric fields in plasmas tend to be very small, although where double layers are formed, the potential drop can be large enough to accelerate ions to relativistic velocities and produce synchrotron radiation such as x-rays and gamma rays. This results in the important concept of quasineutrality, which says that, on the one hand, it is a very good approximation to assume that the density of negative charges is equal to the density of positive charges (

n_e=\langle Z\rangle n_i

), but that, on the other hand, electric fields can be assumed to exist as needed for the physics at hand. The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the Boltzmann relation,

n_e \propto e^

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

\vec = (k_BT_e/e)(\nabla n_e/n_e)

. It is, of course, possible to produce a plasma that is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise it will be dissipated by the repulsive electrostatic force. In astrophysical plasmas, Debye screening prevents electric fields from directly affecting the plasma over large distances (ie. greater than the Debye length). But the existence of charged particles causes the plasma to generate and be affected by magnetic fields. This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object that separates charge over a few tens of Debye lengths. The dynamics of plasmas interacting with external and self-generated magnetic fields are studied in the academic discipline of magnetohydrodynamics.

In contrast to the gas phase

Plasma is often called the fourth state of matter. It is distinct from the three lower-energy phases of matter; solid, liquid, and gas, although it is closely related to the gas phase in that it also has no definite form or volume. There is still some disagreement as to whether a plasma is a distinct state of matter or simply a type of gas. Most physicists consider a plasma to be more than a gas because of a number of distinct properties including the following:

Property	Gas	Plasma
Electrical Conductivity	Very low	Very high For many purposes the electric field in a plasma may be treated as zero, although when current flows the voltage drop, though small, is finite, and density gradients are usually associated with an electric field according to the Boltzmann relation. The possibility of currents couples the plasma strongly to magnetic fields, which are responsible for a large variety of structures such as filaments, sheets, and jets. Collective phenomena are common because the electric and magnetic forces are both long-range and potentially many orders of magnitude stronger than gravitational forces.
Independently acting species	One	Two or three Electrons, ions, and neutrals can be distinguished by the sign of their charge so that they behave independently in many circumstances, having different velocities or even different temperatures, leading to new types of waves and instabilities, among other things
Velocity distribution	Maxwellian	May be non-Maxwellian Whereas collisional interactions always lead to a Maxwellian velocity distribution, electric fields influence the particle velocities differently. The velocity dependence of the Coulomb collision cross section can amplify these differences, resulting in phenomena like two-temperature distributions and run-away electrons.
Interactions	Binary Two-particle collisions are the rule, three-body collisions extremely rare.	Collective Each particle interacts simultaneously with many others. These collective interactions are about ten times more important than binary collisions.

Complex plasma phenomena

Boltzmann relation. Langmuir coined the name plasma because of its similarity to blood plasma, and Hannes Alfvén noted its cellular nature. Note also the filamentary blue outer shell of X-ray emitting high-speed electrons]] Plasma may exhibit complex behaviour. And just as plasma properties scale over many orders of magnitude (see table above), so do these complex features. Many of these features were first studied in the laboratory, and in more recent years, have been applied to, and recognised throughout the universe. Some of these features include:
- Filamentation, the striations or "stringy things" seen in a "plasma ball", the aurora, lightning, electric arcs, and nebulae. They are caused by larger current densities, and are also called magnetic ropes or plasma cables.
- Double layers, localised charge separation regions that have a large potential difference across the layer, and a vanishing electric field on either side. Double layers are found between adjacent plasmas regions with different physical characteristics, and can accelerate ions and produce synchrotron radiation (such as x-rays and gamma rays).
- Birkeland currents, a magnetic-field-aligned electric current, first observed in the Earth's aurora, and also found in plasma filaments.
- Circuits. Birkeland currents imply electric circuits, that follow Kirchhoff's circuit laws. Circuits have a resistance and inductance, and the behaviour of the plasma depends on the entire circuit. Such circuits also store inductive energy, and should the circuit be disrupted, for example, by a plasma instability, the inductive energy will be released in the plasma.
- Cellular structure. Plasma double layers 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.
- Critical ionization velocity in which the relative velocity between an ionized plasma and a neutral gas, may cause further ionization of the gas, resulting in a greater influence of electomagnetic forces.

Ultracold plasmas

It is also possible to create ultracold plasmas, by using lasers to trap and cool neutral atoms to temperatures of 1 mK or lower. Another laser then ionizes the atoms by giving each of the outermost electrons just enough energy to escape the electrical attraction of its parent ion. 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 behaviour that are pushing the limits of our knowledge of plasma physics.

Mathematical descriptions

Plasmas may be usefully described with various levels of detail. However the plasma itself is described, if electric or magnetic fields are present, then Maxwell's equations will be needed to describe them. The coupling of the description of a conductive fluid to electromagnetic fields is known generally as magnetohydrodynamics, or simply MHD.

Fluid

The simplest possibility is to treat the plasma as a single fluid governed by the Navier Stokes Equations. A more general description is the two-fluid picture, where the ions and electrons are considered to be distinct.

Kinetic

For some cases the fluid description is not sufficient. Kinetic models include information on distortions of the velocity distribution functions with respect to a Maxwell-Boltzmann distribution. This may be important when currents flow, when waves are involved, or when gradients are very steep.

Particle-in-cell

Particle-in-cell (PIC) models include kinetic information by following the trajectories of a large number of individual particles. Charge and current densities are determined by summing the particles in cells which are small compared to the problem at hand but still contain many particles. The electric and magnetic fields are found from the charge and current densities with appropriate boundary conditions. PIC codes for plasma applications were developed at Los Alamos National Laboratory in the 1950's. Although often more calculationally intensive than alternative models, they are relatively easy to understand and program and can be very general.

Fundamental plasma parameters

Los Alamos National Laboratory All quantities are in Gaussian cgs units except temperature expressed in eV and ion mass expressed in units of the proton mass

\mu = m_i/m_p

; Z is charge state; k is Boltzmann's constant; K is wavelength; γ is the adiabatic index; ln Λ is the Coulomb logarithm.

Frequencies

- electron gyrofrequency, the angular frequency of the circular motion of an electron in the plane perpendicular to the magnetic field: :

\omega_ = eB/m_ec = 1.76 \times 10^7 B \mbox

- ion gyrofrequency, the angular frequency of the circular motion of an ion in the plane perpendicular to the magnetic field: :

\omega_ = eB/m_ic = 9.58 \times 10^3 Z \mu^ B \mbox

- electron plasma frequency, the frequency with which electrons oscillate when their charge density is not equal to the ion charge density (plasma oscillation): :

\omega_ = (4\pi n_ee^2/m_e)^ = 5.64 \times 10^4 n_e^ \mbox

- ion plasma frequency: :

\omega_ = (4\pi n_iZ^2e^2/m_i)^ = 1.32 \times 10^3 Z \mu^ n_i^ \mbox

- electron trapping rate :

\nu_ = (eKE/m_e)^ = 7.26 \times 10^8 K^ E^ \mbox^

- ion trapping rate :

\nu_ = (ZeKE/m_i)^ = 1.69 \times 10^7 Z^ K^ E^ \mu^ \mbox^

- electron collision rate :

\nu_e = 2.91 \times 10^ n_e\,\ln\Lambda\,T_e^ \mbox^

- ion collision rate :

\nu_i = 4.80 \times 10^ Z^4 \mu^ n_i\,\ln\Lambda\,T_i^ \mbox^

Lengths

plasma oscillation http://history.nasa.gov/SP-345/ch15.htm#250 Ref]]
- Electron thermal de Broglie wavelength, approximate average de Broglie wavelength of electrons in a plasma: :

\Lambda_e= \sqrt= 6.919\times 10^\,T_e^\,\mbox

- classical distance of closest approach, the closest that two particles with the elementary charge come to each other if they approach head-on and each have a velocity typical of the temperature, ignoring quantum-mechanical effects: :

e^2/kT=1.44\times10^\,T^\,\mbox

- electron gyroradius, the radius of the circular motion of an electron in the plane perpendicular to the magnetic field: :

r_e = v_/\omega_ = 2.38\,T_e^B^\,\mbox

- ion gyroradius, the radius of the circular motion of an ion in the plane perpendicular to the magnetic field: :

r_i = v_/\omega_ = 1.02\times10^2\,\mu^Z^T_i^B^\,\mbox

- plasma skin depth, the depth in a plasma to which electromagnetic radiation can penetrate: :

c/\omega_ = 5.31\times10^5\,n_e^\,\mbox

- Debye length, the scale over which electric fields are screened out by a redistribution of the electrons: :

\lambda_D = (kT/4\pi ne^2)^ = 7.43\times10^2\,T^n^\,\mbox

Velocities

- electron thermal velocity, typical velocity of an electron in a Maxwell-Boltzmann distribution: :

v_ = (kT_e/m_e)^ = 4.19\times10^7\,T_e^\,\mbox

- ion thermal velocity, typical velocity of an ion in a Maxwell-Boltzmann distribution: :

v_ = (kT_i/m_i)^ = 9.79\times10^5\,\mu^T_i^\,\mbox

- ion sound velocity, the speed of the longitudinal waves resulting from the mass of the ions and the pressure of the electrons: :

c_s = (\gamma ZkT_e/m_i)^ = 9.79\times10^5\,(\gamma ZT_e/\mu)^\,\mbox

- Alfven velocity, the speed of the waves resulting from the mass of the ions and the restoring force of the magnetic field: :

v_A = B/(4\pi n_im_i)^ = 2.18\times10^\,\mu^n_i^B\,\mbox

Dimensionless

waves meeting the heliopause]]
- square root of electron/proton mass ratio :

(m_e/m_p)^ = 2.33\times10^ = 1/42.9

- number of particles in a Debye sphere :

(4\pi/3)n\lambda_D^3 = 1.72\times10^9\,T^n^

- Alven velocity/speed of light :

v_A/c = 7.28\,\mu^n_i^B

- electron plasma/gyrofrequency ratio :

\omega_/\omega_ = 3.21\times10^\,n_e^B^

- ion plasma/gyrofrequency ratio :

\omega_/\omega_ = 0.137\,\mu^n_i^B^

- thermal/magnetic energy ratio :

\beta = 8\pi nkT/B^2 = 4.03\times10^\,nTB^

- magnetic/ion rest energy ratio :

B^2/8\pi n_im_ic^2 = 26.5\,\mu^n_i^B^2

Miscellaneous

- Bohm diffusion coefficient :

D_B = (ckT/16eB) = 6.25\times10^6\,TB^\,\mbox^2/\mbox

- transverse Spitzer resistivity :

\eta_\perp = 1.15\times10^\,Z\,\ln\Lambda\,T^\,\mbox = 1.03\times10^\,Z\,\ln\Lambda\,T^\,\Omega\,\mbox

Fields of active research

Bohm diffusion is so effective at accelerating ions, that electric fields are used in ion drives]] This is just a partial list of topics. A more complete and organised list can be found on the Web site for Plasma science and technology [http://www.plasmas.com/topics.htm].
- Plasma theory
- Plasma equilibria and stability
- Plasma interactions with waves and beams
- Guiding center
- adiabatic invariant
- Debye sheath
- Coulomb collision
- Plasmas in nature
- The Earth's ionosphere
- Space plasmas, e.g. Earth's plasmasphere (an inner portion of the magnetosphere dense with plasma)
- plasma cosmology
- Plasma sources
- Dusty Plasmas
- Plasma diagnostics
- Thomson scattering
- Langmuir probe
- Spectroscopy
- Interferometry
- Ionospheric heating
- Incoherent scatter radar
- Plasma applications
- Fusion power
- Magnetic fusion energy (MFE) -- tokamak, stellarator, reversed field pinch, magnetic mirror, dense plasma focus
- Inertial fusion energy (IFE) (also Inertial confinement fusion — ICF)
- Plasma-based weaponry
- Industrial plasmas
- plasma chemistry
- plasma processing
- plasma display

External links

- [http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasma4StateMatter.html Plasmas: the Fourth State of Matter]
- [http://www.plasmas.org/ Plasma Science and Technology]
- [http://plasma-gate.weizmann.ac.il/PlasmaI.html Plasma on the Internet] comprehensive list of plasma related links.
- [http://farside.ph.utexas.edu/teaching/plasma/lectures/lectures.html Introduction to Plasma Physics: a graduate level lecture course given by Richard Fitzpatrick]
- [http://plasmas.org/ An overview of plasma links and applications]
- [http://wwwppd.nrl.navy.mil/nrlformulary/index.html NRL Plasma Formulary online] (or an [http://w3.pppl.gov/~dcoster/nrl/ html version])
- [http://www.plasmacoalition.org/ Plasma Coalition page]
- [http://starfire.ne.uiuc.edu/ Plasma Material Interaction]
- [http://jnaudin.free.fr/html/oa_plasmoid.htm How to build a Stable Plasmoid at One Atmosphere] (requires pre-ignition)
- [http://jnaudin.free.fr/html/oa_plsm4.htm How to build a Stable Plasmoid with this Enhanced Generator] (self-igniting)
- [http://c3po.barnesos.net/homepage/lpl/grapeplasma/ How to make a glowing ball of plasma in your microwave with a grape] Category:Astrophysics ko:플라즈마 ja:プラズマ

Celestial body atmosphere

Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. The gases are attracted by the gravity of the body, and held fast if gravity is sufficient and the atmosphere's temperature is low. Some planets consist mainly of various gases, and thus have very deep atmospheres (see gas giant). Earth, Venus, Mars, and Pluto have atmospheres that envelop their surfaces, as do three of the satellites of the outer planets: Titan, Enceladus (moons of Saturn), and Triton (a moon of Neptune). In addition, the giant planets of the outer solar system - Jupiter, Saturn, Uranus, and Neptune - are composed predominantly of gases. Other bodies in the solar system possess extremely thin atmospheres. Such bodies are the Moon (sodium gas), Mercury (sodium gas), Europa (oxygen) and Io (sulfur). Initial atmospheric makeup is generally related to the chemistry and temperature of the local solar nebula during planetary formation and the subsequent escape of interior gases. These original atmospheres underwent much evolution over time, with the varying properties of each planet resulting in very different outcomes. Surface gravity, the force that holds down an atmosphere, differs significantly among the planets. For example, the large gravitational force of the giant planet Jupiter is able to retain light gases such as hydrogen and helium that escape from lower gravity objects. Second, the distance from the sun determines the energy available to heat atmospheric gas to the point where its molecules' thermal motion exceed the planet's escape velocity, the speed at which gas molecules overcome a planet's gravitational grasp. Thus, the distant and cold Titan, Triton, and Pluto are able to retain their atmospheres despite relatively low gravities. Since a gas at any particular temperature will have molecules moving at a wide range of velocities, there will almost always be some slow leakage of gas into space. Lighter molecules move faster than heavier ones with the same thermal kinetic energy, and so gases of low molecular weight are lost more rapidly than those of high molecular weight. It is thought that Venus and Mars may have both lost much of their water when, after being photodissociated into hydrogen and oxygen by solar ultraviolet, the hydrogen escaped. Earth's magnetic field helps to prevent this, as the solar wind greatly enhances the escape of hydrogen. Other mechanisms that can cause atmosphere depletion are solar wind-induced sputtering, impact erosion, weathering, and sequestration—sometimes referred to as "freezing out"—into the regolith and polar caps. Moreover, on Earth, atmospheric composition is largely governed by the by-products of the very life that it sustains. From the perspective of the planetary geologist, atmospheres are important in the ways they shape planetary surfaces. Wind can transport particles, both eroding the surface and leaving deposits (eolian processes). Frost and precipitation can leave direct and indirect marks on a planetary surface. Climate changes can influence a planet's geological history. Conversely, studying surface geology leads to an understanding of the atmosphere and climate of a planet - both its present state and its past. Interstellar planets, theoretically, may also retain thick atmospheres.

Star

:This article is about celestial bodies. A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. Unlike a planet, from which most light is reflected, a star emits light because of its intense heat. Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion. Small (dwarf) stars such as the Sun generally have essentially featureless disks with only small starspots. Larger (giant) stars have much bigger, much more obvious starspots, and also exhibit strong stellar limb-darkening (the brightness decreases towards the edge of the stellar disk). Stellar astronomy is the study of stars.

Star formation and evolution

Star formation occurs in molecular clouds, large regions of high density in the interstellar medium (though still less dense than the inside of an earthly vacuum chamber). Star formation begins with gravitational instability inside those clouds, often triggered by shockwaves from supernovae or collision of two galaxies (as in a starburst galaxy). High mass stars powerfully illuminate the clouds from which they formed. One example of such a nebula is the Orion Nebula. Stars spend about 90% of their lifetime fusing hydrogen to produce helium in high-temperature and high-pressure reactions near the core. Such stars are said to be on the main sequence. Small stars (called red dwarfs) burn their fuel very slowly and last tens to hundreds of billions of years. At the end of their lives, they simply become dimmer and dimmer, fading into black dwarfs. However, since the lifespan of such stars is greater than the current age of the universe (13.6 billion years), no black dwarfs exist yet. As most stars exhaust their supply of hydrogen, their outer layers expand and cool to form a red giant. In about 5 billion years, when the Sun is a red giant, it will be so large that it will consume both Mercury and Venus. Eventually the core is compressed enough to start helium fusion, and the star heats up and contracts. Larger stars will also fuse heavier elements, all the way to iron, which is the end point of the process. Since iron nuclei are more tightly bound than any heavier nuclei, they cannot be fused to release energy. Likewise, since they are more tightly bound than all lighter nuclei, energy cannot be released by fission. In old, very massive stars, a large core of inert iron will accumulate in the center of the star. An average-size star will then shed its outer layers as a planetary nebula. The core that remains will be a tiny ball of degenerate matter not massive enough for further fusion to take place, supported only by degeneracy pressure, called a white dwarf. These too will fade into black dwarfs over very long stretches of time. white dwarf In larger stars, fusion continues until an iron core accumulates that is too large to be supported by electron degeneracy pressure. This core will suddenly collapse as its electrons are driven into its protons, forming neutrons and neutrinos in a burst of inverse beta decay. The shockwave formed by this sudden collapse causes the rest of the star to explode in a supernova. Supernovae are so bright that they may briefly outshine the star's entire home galaxy. When they occur within the Milky Way, supernovae have historically been observed by naked-eye observers as "new stars" where none existed before. Eventually, most of the matter in a star is blown away by the explosion (forming nebulae such as the Crab Nebula) and what remains will be a neutron star (sometimes a pulsar or X-ray burster) or, in the case of the largest stars, a black hole. The blown-off outer layers of dying stars include heavy elements which may be recycled during new star formation. These heavy elements allow the formation of rocky planets. The outflow from supernovae and the stellar wind of large stars play an important part in shaping the interstellar medium.

Appearance and distribution of stars

All stars except the Sun appear to the human eye as shining points in the nighttime sky that twinkle because of the effect of the Earth's atmosphere. Interferometer telescopes are required in order to produce images of these objects. The Sun is also a star, but it is close enough to Earth to appear as a disk instead, and to provide daylight. Stars are not spread uniformly across the universe, but are typically grouped into galaxies. A typical galaxy contains hundreds of billions of stars. The majority of stars are gravitationally bound to other stars, forming binary stars. Larger groups called star clusters also exist. Astronomers estimate that there are at least 70 sextillion (7×10²²) stars in the known universe [http://news.bbc.co.uk/2/hi/science/nature/3085885.stm]. That is 70 000 000 000 000 000 000 000, or 230 billion times as many as the 300 billion in our own Milky Way. The nearest star to the Earth, apart from the Sun, is Proxima Centauri, which is 39.9 trillion kilometers, or 4.2 light years away (light from Proxima Centauri takes 4.2 years to reach Earth). Travelling at the orbit speed of the Space Shuttle (5 miles per second -- almost 30,000 kilometers per hour), it would take about 150,000 years to get there. Distances like this are typical inside galactic discs, where the Sun and Earth are located. Stars can be much closer to each other in the centres of galaxies and globular clusters, or much further apart in galactic halos.

Age and size of stars

galactic halo Many stars are between 1 billion and 10 billion years old. Some stars may even be close to 13.7 billion years old, which is the observed age of the universe. (See Big Bang theory and stellar evolution.) They range in size from the tiny neutron stars (which are actually dead stars) no bigger than a city, to supergiants like the North Star (Polaris) and Betelgeuse, in the Orion constellation, which have a diameter about 1,000 times larger than the Sun—about 1.6 billion kilometers. However, these have a much lower density than the Sun. One of the most massive stars known is η Carinae, with 100–150 times as much mass as the Sun. Recent work by Donald Figer, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, suggests that 150 solar masses is the upper limit of stars in the current era of the universe. He used the Hubble Space Telescope to observe about a thousand stars in the Arches cluster, a massive young star cluster near the core of the Milky Way, and found no stars over that limit despite a statistical expectation that there should be several. The reason for this limit is not precisely known, but the Eddington limit is part of the answer. The very first stars to form after the Big Bang may have been larger, up to 300 solar masses or more, due to the complete absence of elements heavier than lithium in their composition. This generation of supermassive star is long extinct, however, and currently only theoretical. With a mass only 93 times that of Jupiter, AB Doradus C, a companion to AB Doradus A, is the smallest known star undergoing nuclear fusion in its core. Smaller bodies are brown dwarfs, which occupy a poorly-defined grey area between stars and gas giants. The minimum mass a star can have is estimated to be in the vicinity of 75 Jupiters.

Star classification

There are different classifications of stars ranging from type W, which are very large and bright, to M, which is often just large enough to start ignition of the hydrogen. Some of the more common classifications are O, B, A, F, G, K, M, and can perhaps be more easily remembered using the mnemonic "Oh, Be A Fine Girl, Kiss Me" (variant: change "girl" to "guy"), invented by Annie Jump Cannon (1863-1941). There are many other mnemonics for star classification; the most frequent addition tacks "Right Now, Sweetheart" for the red dwarf sub-types R, N and S. The new types L and T have also been recently appended to the end of the OBAFGKM sequence to classify the coldest low-mass stars and brown dwarfs, prompting such additions as "Lovingly Tonight" to the mnemonic. Each letter has 10 subclassifications. Our Sun is a G2, which is very near the middle in terms of quantities observed. Most stars fall into the main sequence which is a description of stars based on their absolute magnitude and spectral type. The Sun is taken as the prototypical star (not because it is special in any way, but because it is the closest and most studied star we have), and most characteristics of other stars are usually given in solar units.
For example, the mass of the Sun is :M_Sun = 1.9891×10³⁰ kg The masses of other stars can be given in terms of M_Sun.

Naming of stars

Most stars are identified only by catalogue numbers; only a few have names as such. The names are either traditional names (mostly from Arabic), Flamsteed designations, or Bayer designations. The only body which has been recognized by the scientific community as having competence to name stars or other celestial bodies is the International Astronomical Union (IAU). A number of private companies (e.g. the "International Star Registry") purport to sell names to stars; however, these names are not recognized by the scientific community, nor used by them, and many in the astronomy community view these organizations as frauds preying on people ignorant of how stars are in fact named. See star designations for more information on how stars are named. For a list of traditional names, see the list of stars by constellation.

Energy production

The energy produced by stars radiates into space as electromagnetic radiation, as a stream of neutrinos from the star's core, and as a stream of particles from the star's outer layers (its stellar wind). The peak frequency of the light depends on the temperature of the outer layers of the star. Besides the emitted visible light, the ultraviolet and infrared components are typically significant. The apparent brightness of a star is measured by its apparent magnitude.

Nuclear fusion reaction pathways

A variety of different nuclear fusion reactions take place inside the cores of stars, depending upon their mass and composition (see Stellar nucleosynthesis). Stars begin as a cloud of mostly hydrogen with about 25% helium and heavier elements in smaller quantities. In the Sun, with a 10⁷ K core, hydrogen fuses to form helium in the proton-proton chain: :4¹H → 2²H + 2e⁺ + 2ν_e (4.0 MeV + 1.0 MeV) :2¹H + 2²H → 2³He + 2γ (5.5 MeV) :2³He → ⁴He + 2¹H (12.9 MeV) These reactions result in the overall reaction: :4¹H → ⁴He + 2e⁺ + 2γ + 2ν_e (26.7 MeV) In more massive stars, helium is produced in a cycle of reactions catalyzed by carbon, the carbon-nitrogen-oxygen cycle. In stars with cores at 10⁸ K and masses between 0.5 and 10 solar masses, helium can be transformed into carbon in the triple-alpha process: :⁴He + ⁴He + 92 keV → ^{8
-}Be :⁴He + ^{8
-}Be + 67 keV → ^{12
-}C :^{12
-}C → ¹²C + γ + 7.4 MeV For an overall reaction of: :3⁴He → ¹²C + γ + 7.2 MeV

Star mythology

As well as certain constellations and the Sun itself, stars as a whole have their own mythology. They were thought to be the souls of the dead, or gods/goddesses.

References

- Cliff Pickover (2001) "The Stars of Heaven", Oxford University Press
- John Gribbin, Mary Gribbin (2001) "Stardust: Supernovae and Life — The Cosmic Connection", Yale University Press.

External links

- [http://www.mrao.cam.ac.uk/telescopes/coast/betel.html Images of starspots on the surface of Betelgeuse]
- [http://simbad.u-strasbg.fr/sim-fid.pl Find out what is known about any given star by entering its name or position]
- [http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml Star Classification] Category:Astronomical objects ko:항성 ms:Bintang ja:恒星 simple:Star th:ดาวฤกษ์

Electrons

The electron is a fundamental subatomic particle which carries a negative electric charge.

Overview

Within an atom the electrons surround the nucleus of protons and neutrons in an electron configuration. The word electron was coined in 1894 and is derived from the term electric, whose ultimate origin is the Greek word 'ηλεκτρον, meaning amber. Electrons in motion constitute electric current which may be used by scientists and engineers to measure many physical properties. Electric current existing for a finite time gives rise to a movement of charge (electricity) that may be harnessed as a practical means to perform work. The variations in electric field generated by differing numbers of electrons and their configurations in atoms determine the chemical properties of the elements. These fields play a fundamental role in chemical bonds and chemistry.

Electrons in practice

Classification of electrons

The electron is one of a class of subatomic particles called leptons which are believed to be fundamental particles (that is, they cannot be broken down into smaller constituent parts). The word "particle" is somewhat misleading however, because quantum mechanics shows that electrons also behave like a wave, e.g. in the double-slit experiment; this is called wave-particle duality. The antiparticle of an electron is the positron, which has the same mass but positive rather than negative charge. The term negatron is sometimes used to refer to standard electrons so that the term electron may be used to describe both positrons and negatrons, as proposed by Carl D. Anderson. Under ordinary circumstances, however, electron refers to the negatively charged particle alone.

Properties and behavior of electrons

Electrons have a negative electric charge of −1.6 × 10⁻¹⁹ coulombs, and a mass of about 9.11 × 10⁻³¹ kg (0.51 MeV/c²), which is approximately ¹⁄₁₈₃₆ of the mass of the proton. These are commonly represented as e⁻. According to quantum mechanics, electrons can be represented by wavefunctions, from which the electron density can be determined. The exact momentum and position of an electron cannot be simultaneously determined. This is a limitation described by the Heisenberg uncertainty principle, which, in this instance, simply states that the more accurately we know a particle's position, the less accurately we can know its momentum and vice versa. The electron has spin ½, which implies it is a fermion, i.e., it follows the Fermi-Dirac statistics. While most electrons are found in atoms, others move independently in matter, or together as an electron beam in a vacuum. In some superconductors, electrons move in Cooper pairs, in which their motion is coupled to nearby matter via lattice vibrations called phonons. When electrons move, free of the nuclei of atoms, and there is a net flow, this flow is called electricity, or an electric current. A body has a static charge when the body has more or fewer electrons than are required to balance the positive charge of the nuclei. When there is an excess of electrons, the object is said to be negatively charged. When there are fewer electrons than protons, the object is said to be positively charged. When the number of electrons and the number of protons are equal, their charges cancel out and the object is said to be electrically neutral. A macroscopic body can acquire charge through rubbing, i.e. the phenomena of triboelectricity. Electrons and positrons can annihilate each other and produce a pair of photons. Conversely, high-energy photons may transform into an electron and a positron by a process called pair production. The electron is an elementary particle — that means that it has no substructure (at least, experiments have not found any so far, and there is good reason to believe that there is not any). Hence, it is usually described as point-like, i.e. with no spatial extension. However, if one gets very near an electron, one notices that its properties (charge and mass) seem to change. This is an effect common to all elementary particles: the particle influences the vacuum fluctuations in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects (see renormalization). There is a physical constant called the classical electron radius, with a value of 2.8179 × 10⁻¹⁵ m. Note that this is the radius that one could infer from its charge if the physics were only described by the classical theory of electrodynamics and there were no quantum mechanics (hence, it is an outdated concept that nevertheless sometimes still proves useful in calculations). The speed of an electron in a vacuum can approach, but never reach c, the speed of light in a vacuum. This is due to an effect of special relativity. The effects of special relativity are based on a quantity known as gamma or the Lorentz factor. Gamma is a function of v, the velocity of the particle, and c. The following is the formula for gamma: :

\gamma = 1 / \sqrt

The energy necessary to accelerate a particle is gamma minus one times the rest mass. For example, the linear accelerator at Stanford can [http://www2.slac.stanford.edu/vvc/theory/relativity.html accelerate] an electron to roughly 51 GeV. This gives you a gamma of 100,000 given that the rest mass of an electron is 0.51 MeV/c² (the relativistic mass of this fast electron is 100 000 times its rest mass). Solving the equation above for the speed of the electron gives a speed of: :

(1-\frac   \gamma ^)c

= 0.999 999 999 95 c. (The formula applies for large γ.)

Electrons in the universe

It is believed that the number of electrons existing in the known universe is at least 10⁷⁹. This number amounts to a density of about one electron per cubic metre of space. Based on the classical electron radius and assuming a dense sphere packing, it can be calculated that the number of electrons that would fit in the observable universe is on the order of 10¹³⁰. Of course, this number is even less meaningful than the classical electron radius itself.

Electrons in industry

Electron beams are used in welding as well as lithography.

Electrons in the laboratory

Early experiments

The quantum or discrete nature of electron's charge was observed by Robert Millikan in the Oil-drop experiment of 1909.

Use of electrons in the laboratory

Electron microscopes are used to magnify details up to 500,000 times. Quantum effects of electrons are used in Scanning tunneling microscope to study features at the atomic scale.

Electrons in theory

In relativistic quantum mechanics, the electron is described by the Dirac Equation. Quantum electrodynamics (QED) models an electron as a charged particle surrounded a sea of interacting virtual particles, modifying the sea of virtual particles which makes up a vacuum. Although this theory involves difficult theoretical problems where calculations produce infinite terms, a practical (although mathematically dubious) method called renormalization was discovered whereby infinite terms can be cancelled to produce finite predictions about the electron. The correction of just over 0.1% to the predicted value of the electron's gyromagnetic ratio from exactly 2 (as predicted by Dirac's single particle model), and its extraordinarily precise agreement with the experimentally determined value, is viewed as one of the pinnacles of modern physics. There are now indications that string theory and its descendants may provide a model of the electron and other fundamental particles where the infinities in calculations do not appear, because the electron is no longer seen as a dimensionless point. At present, string theory is very much a 'work in progress' and lacks predictions analogous to those made by QED that can be experimentally verified. In the Standard Model of particle physics, it forms a doublet in SU(2) with the electron neutrino, as they interact through the weak interaction. The electron has two more massive partners, with the same charge but different masses: the muon and the tau lepton. The antimatter counterpart of the electron is its antiparticle, the positron. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When an electron and a positron meet, they may annihilate each other, giving rise to two gamma-ray photons, each having an energy of 0.511 MeV (511 keV). See also Electron-positron annihilation. Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems, and for classical modelling of microscopic systems.

History

The electron as a unit of charge in electrochemistry had been posited by G. Johnstone Stoney in 1874. In 1894, he also invented the word itself. The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying "cathode rays". Influenced by the work of James Clerk Maxwell, and the discovery of the X-ray, he deduced that cathode rays existed and were negatively charged "particles", which he called "corpuscles". He published his discovery in 1897. The periodic law states that the chemical properties of elements largely repeat themselves periodically and is the foundation of the periodic table of elements. The law itself was initially explained by the atomic mass of the elements. However, as there were anomalies in the periodic table, efforts were made to find a better explanation for it. In 1913, Henry Moseley introduced the concept of the atomic number and explained the periodic law with the number of protons each element has. In the same year, Niels Bohr showed that electrons are the actual foundation of the table. In 1916, Gilbert Newton Lewis and Irving Langmuir explained the chemical bonding of elements by electronic interactions.

External links

- [http://www.aip.org/history/electron/ The Discovery of the Electron] from the American Institute of Physics History Center
- [http://pdg.lbl.gov/ Particle Data Group]
- Stoney, G. Johnstone, "[http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Stoney-1894.html Of the 'Electron,' or Atom of Electricity]". Philosophical Magazine. Series 5, Volume 38, p. 418-420 October 1894.
- Eric Weisstein's World of Physics: [http://scienceworld.wolfram.com/physics/Electron.html Electron]

References

-
-
- Brumfiel, G. (6 January 2005). Can electrons do the splits? In Nature, 433, 11. ko:전자 ja:電子 simple:Electron th:อิเล็กตรอน

Electron-volt

An electronvolt (symbol: eV) is the amount of kinetic energy gained by a single unbound electron when it passes through an electrostatic potential difference of one volt, in vacuum. The one-word spelling is the modern recommendation; the use of the earlier electron volt still exists. This is a very small amount of energy: : 1 eV = 1.602 176 53 (14) × 10⁻¹⁹ J. (Source: CODATA 2002 recommended values) It is a non-SI unit of energy, accepted for use with SI.

Using electronvolts to measure mass

Einstein reasoned that energy is equivalent to (rest) mass, as famously expressed in the formula E=mc² (1 kg = 90 petajoules). It is thus common in particle physics, where mass and energy are often interchanged, to use eV/c² or even simply eV as a unit of mass. (The latter is often paired with natural units where c=1, but this is not strictly necessary.) For example, an electron and a positron, each with a mass of 0.511 MeV, can annihilate to yield 1.022 MeV of energy. The proton, a typical baryon, has a mass of 0.938 GeV, making GeV (often pronounced jev) a very convenient unit of mass for particle physics. :1 eV/c² = 1.783 × 10⁻³⁶ kg :1 keV/c² = 1.783 × 10⁻³³ kg :1 MeV/c² = 1.783 × 10⁻³⁰ kg :1 GeV/c² = 1.783 × 10⁻²⁷ kg

Electronvolts and kinetic energy

For comparison:
- 3.2 × 10⁻¹¹ joule or 200 MeV - total energy released in nuclear fission of one U-235 atom (on average, it depends on the precise break up)
- 3.5 × 10⁻¹¹ joule or 210 MeV - total energy released in fission of one Pu-239 atom (on average, it depends on the precise break up)
- Molecular bond energies are on the order of an electronvolt per molecule.
- The typical atmospheric molecule has an energy of about 0.03 eV. This corresponds to room temperature. To convert a particle's kinetic energy in electronvolts into its temperature in kelvins, multiply by 11,605 (see Boltzmann constant).

External links

- [http://www1.bipm.org/en/si/si_brochure/chapter4/table7.html BIPM's definition of the electronvolt]
- [http://www.projects.ex.ac.uk/trol/scol/index.htm Conversion Calculator for Units of ENERGY]
- http://physics.nist.gov/cuu/Constants physical constants reference; CODATA data Category:Units of energy ko:전자볼트 ja:電子ボルト

Geomagnetic storm

A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere. Associated with solar coronal mass ejections (CME), a coronal hole, or solar flare is a solar wind shock wave which arrives 24 to 36 hours after the event. This only happens if the shock wave travels in a direction toward Earth. The solar wind pressure on the magnetosphere will increase or decrease depending on the Sun's activity. Solar wind pressure changes modify the electric currents in the ionosphere. Magnetic storms last 24 to 48 hours, but some may last for many days. solar wind]

Interactions with planetary processes

The solar wind also carries with it the magnetic field of the Sun. This field will have either a North or South orientation. If the solar wind has energetic bursts, contracting and expanding the magnetosphere, or if the solar wind takes a southward polarization, geomagnetic storms can be expected. The southward field causes magnetic reconnection of the dayside magnetopause, rapidly injecting magnetic and particle energy into the Earth's magnetosphere. During a geomagnetic storm the ionosphere's F₂ layer will become unstable, fragment, and may even disappear. In the Northern and Southern pole regions of the Earth aurora will be observable in the sky. aurora

Geomagnetic storm effects

Radiation hazards to humans

Intense solar flares release very-high-energy particles that can be as injurious to humans as the low-energy radiation from nuclear blasts. Earth's atmosphere and magnetosphere allow adequate protection for us on the ground, but astronauts in space are subject to potentially lethal dosages of radiation. The penetration of high-energy particles into living cells, measured as radiation dose, leads to chromosome damage and, potentially, cancer. Large doses can be fatal immediately. Solar protons with energies greater than 30 MeV are particularly hazardous. In October 1989, the Sun produced enough energetic particles that an astronaut on the Moon, wearing only a space suit and caught out in the brunt of the storm, would probably have died; the expected dose would be about 7000 rem. (Astronauts who had time to gain safety in a shelter beneath moon soil would have absorbed only slight amounts of radiation.) The astronauts on the Mir station were subjected to daily doses of about twice the yearly dose on the ground, and during the solar storm at the end of 1989 they absorbed their full-year radiation dose limit in just a few hours. Solar proton events can also produce elevated radiation aboard aircraft flying at high altitudes. Although these risks are small, monitoring of solar proton events by satellite instrumentation allows the occasional exposure to be monitored and evaluated, and eventually the flight paths and altitudes adjusted in order to lower the absorbed dose of the flight crews.

Climate

The Sun is the heat engine that drives the circulation of our atmosphere. Although it has long been assumed to be a constant source of energy, recent measurements of this solar constant have shown that the base output of the Sun can vary by up to two tenths of a percent over the 11-year solar cycle. Temporary decreases of up to one-half percent have been observed. Atmospheric scientists say that this variation is significant and that it can modify climate over time. Plant growth has been shown to vary over the 11-year sunspot and 22-year magnetic cycles of the Sun, as evidenced in tree-ring records. While the solar cycle has been nearly regular during the last 300 years, there was a period of 70 years during the 17th and 18th centuries when very few sunspots were seen (even though telescopes were widely used). This drop in sunspot number coincided with the timing of the Little Ice Age in Europe, implying a Sun-to-climate connection. Recently, a more direct link between climate and solar variability has been speculated. Stratospheric winds near the equator blow in different directions, depending on the time in the solar cycle. Studies are under way to determine how this wind reversal affects global circulation patterns and weather. During proton events, many more energetic particles reach Earth's middle atmosphere. There they cause molecular ionization, creating chemicals that destroy atmospheric ozone and allow increased amounts of harmful solar ultraviolet radiation to reach Earth's surface. A solar proton event in 1982 resulted in a temporary 70% decrease in ozone densities.

Biology

There is a growing body of evidence that changes in the geomagnetic field affect biological systems. Studies indicate that physically stressed human biological systems may respond to fluctuations in the geomagnetic field. Interest and concern in this subject have led the Union of Radio Science International to create a new commission entitled Electromagnetics in Biology and Medicine. Possibly the most closely studied of the variable Sun's biological effects has been the degradation of homing pigeons' navigational abilities during geomagnetic storms. Pigeons and other migratory animals, such as dolphins and whales, have internal biological compasses composed of the mineral magnetite wrapped in bundles of nerve cells. While this probably is not their primary method of navigation, there have been many pigeon race smashes, a term used when only a small percentage of birds return home from a release site. Because these losses have occurred during geomagnetic storms, pigeon handlers have learned to ask for geomagnetic alerts and warnings as an aid to scheduling races.

Disrupted systems

Communications

Many communication systems utilize the ionosphere to reflect radio signals over long distances. Ionospheric storms can affect radio communication at all latitudes. Some radio frequencies are absorbed and others are reflected, leading to rapidly fluctuating signals and unexpected propagation paths. TV and commercial radio stations are little affected by solar activity, but ground-to-air, ship-to-shore, Voice of America, Radio Free Europe, and amateur radio are frequently disrupted. Radio operators using high frequencies rely upon solar and geomagnetic alerts to keep their communication circuits up and running. Some military detection or early warning systems are also affected by solar activity. The over-the-horizon radar bounces signals off the ionosphere in order to monitor the launch of aircraft and missiles from long distances. During geomagnetic storms, this system can be severely hampered by radio clutter. Some submarine detection systems use the magnetic signatures of submarines as one input to their locating schemes. Geomagnetic storms can mask and distort these signals. The Federal Aviation Administration routinely receives alerts of solar radio bursts so that they can recognize communication problems and forego unnecessary maintenance. When an aircraft and a ground station are aligned with the Sun, jamming of air-control radio frequencies can occur. This can also happen when an Earth station, a satellite, and the Sun are in alignment. The telegraph lines in the past were affected by geomagnetic storms as well. The telegraphs used a long wire for the data line, stretching for many miles, using ground as the return wire and being fed with DC power from a battery; this made them (together with the power lines mentioned below) susceptible to being influenced by the fluctuations caused by the ring current. The voltage/current induced by the geomagnetic storm could've led to diminishing of the signal, when subtracted from the battery polarity, or to overly strong and spurious signals when added to it; some operators in such cases even learned to disconnect the battery and rely on the induced current as their power source. In extreme cases the induced current was so high the coils at the receiving side burst in flames, or the operators received electric shocks. Geomagnetic storms affect also long-haul telephone lines, including undersea cables.[http://image.gsfc.nasa.gov/poetry/storm/storms.html]

Navigation systems

Systems such as GPS, LORAN, and OMEGA are adversely affected when solar activity disrupts their signal propagation. The OMEGA system consists of eight transmitters located through out the world. Airplanes and ships use the very low frequency signals from these transmitters to determine their positions. During solar events and geomagnetic storms, the system can give navigators information that is inaccurate by as much as several miles. If navigators are alerted that a proton event or geomagnetic storm is in progress, they can switch to a backup system. GPS signals are affected when solar activity causes sudden variations in the density of the ionosphere, causing the GPS signals to scintillate. The scintillation of satellite signals during ionospheric disturbances is studied at HAARP during ionospheric modification experiments. It has also been studied at the National Science Foundation equatorial ionospheric observation facility in Jicamarca, Peru.

Satellites

Geomagnetic storms and increased solar ultraviolet emission heat Earth's upper atmosphere, causing it to expand. The heated air rises, and the density at the orbit of satellites up to about 1000 km increases significantly. This results in increased drag on satellites in space, causing them to slow and change orbit slightly. Unless Low Earth Orbit satellites are routinely boosted to higher orbits, they slowly fall, and eventually burn up in Earth's atmosphere. Skylab is an example of a spacecraft reentering Earth's atmosphere prematurely as a result of higher-than-expected solar activity. During the great geomagnetic storm of March 1989, four of the Navy's navigational

Solar wind

History

Properties

Fast and slow solar wind

Variability and space weather

Outer limits

References

Notes

See also

Ion Storm Inc.

Games by Ion Storm

See also

External links

Solar Wind (comic)

Reviews

Awards

Spin-offs

External links

Plasma

Common plasmas

Characteristics

Plasma scaling

Temperatures

Densities

Potentials

In contrast to the gas phase

Complex plasma phenomena

Ultracold plasmas

Mathematical descriptions

Fluid

Kinetic

Particle-in-cell

Fundamental plasma parameters

Frequencies

Lengths

Velocities

Dimensionless

Miscellaneous

Fields of active research

See also

External links

Celestial body atmosphere

See also

Star

Star formation and evolution

Appearance and distribution of stars

Age and size of stars

Star classification

Naming of stars

Energy production

Nuclear fusion reaction pathways

Star mythology

References

See also

Related lists

External links

Electrons

Overview

Electrons in practice

Classification of electrons

Properties and behavior of electrons

Electrons in the universe

Electrons in industry

Electrons in the laboratory

Early experiments

Use of electrons in the laboratory

Electrons in theory

History

See also

External links

References

Electron-volt

Using electronvolts to measure mass

Electronvolts and kinetic energy

See also

External links

Geomagnetic storm

Interactions with planetary processes

Geomagnetic storm effects

Radiation hazards to humans