当电离过程频繁发生，使电子和阳离子的浓度达到一定的数值时，物质的状态也就起了根本的变化，它的性质也变得与气体完全不同。为区别于固体、液体和气体这三种状态，我们称物质的这种状态为物质的第四态，又起名叫等离子态。
温度不断升高，气体这时构成分子的原子发生分离，形成为独立的原子，如氮分子会分裂成两个氮原子，我们称这种过程为气体中分子的离解。
如果再进一步升高温度，原子中的电子就会从原子中剥离出来，成为带正电荷的原子核和带负电荷的电子，这个过程称为原子的电离。电离过程的发生，形成了等离子。
扩展资料：等离子态下的物质具有类似于气态的性质，比如良好的流动性和扩散性。但是，由于等离子体的基本组成粒子是离子和电子；
因此它也具有许多区别于气态的性质，比如良好的导电性、导热性。根据科学计算，等离子体的比热容与温度成正比，高温下等离子体的比热容往往是气体的数百倍。
等离子体的用途非常广泛。从我们的日常生活到工业、农业、环保、军事、医学、宇航、能源、天体等方面，它都有非常重要的应用价值。
参考资料：百度百科--等离子
等离子状态，是指物质原子内的电子在高温下脱等离子态在茫茫无际的宇宙空间里，等离子态是一种普遍存在的状态。宇宙中大部分发光的星球内部温度和压力都很高，这些星球内部的物质差不多都处于等离子态。只有那些昏暗的行星和分散的星际物质里才可以找到固态、液态和气态的物质。 就在我们周围，也经常看到等离子态的物质。在日光灯和霓虹灯的灯管里，在眩目的白炽电弧里，都能找到它的踪迹。另外，在地球周围的电离层里，在美丽的极光、大气中的闪光放电和流星的尾巴里，也能找到奇妙的等离子态。 概念当这种电离过程频繁发生，使电子和离子的浓度达到一定的数值时，物质的状态也就起了根本的变化，它的性质也变得与气体完全不同．为区别于固体、液体和气体这三种状态，我们称物质的这种状态为物质的第四态，又起名叫等离子态． 特点等离子态下的物质具有类似于气态的性质，比如良好的流动性和扩散性。但是，由于等离子体的基本组成粒子是离子和电子，因此它也具有许多区别于气态的性质，比如良好的导电性、导热性。特别的，根据科学计算，等离子体的比热与温度成正比，高温下等离子体的比热往往是气体的数百倍。 用途等离子体有什么用处呢？噢！它的用途非常广泛．从我们的日常生活到工业、农业、环保、军事、医学、宇航、能源、天体等方面，它都有非常重要的应用价值．离原子核的吸引，使物质呈正负带电粒子状态存在。等离子显示屏和等离子电视等离子彩电PDP（Plasma Display Panel）是在两张超薄的玻璃板之间注入混合气体，并 壁挂式等离子电视施加电压利用荧光粉发光成像的设备。薄玻璃板之间充填混合气体，施加电压使之产生离子气体，然后使等离子气体放电，与基板中的荧光体发生反应，产生彩色影像。等离子彩电又称“壁挂式电视”，不受磁力和磁场影响，具有机身纤薄、重量轻、屏幕大、色彩鲜艳、画面清晰、亮度高、失真度小、节省空间等优点。 等离子是采用近几年来高速发展的等离子平面屏幕技术的新—代显示设备，目前市场上销售的产品有两种类型，一种是等离子显示屏，另一种是等离子电视，两者在本质上没有太大的区别，唯一的区别是有没有内置电视接收调谐器。 由于PDP发展初期主要是针对商业展示用途，所以当前仍有很多PDP都没有内置电视接收调谐器，也就是说，不能直接接收电视信号。因此如果选择的是这种产品，那么只能通过卫星解码器或录像机等其它设备来兼作电视讯号调谐接收器，也可另购—个电视接收器。现在等离子已经开始面对家庭用户设计生产，目前生产的部分等离子开始内置电视接收器，这些机型预先就设有RF射频连接端子，可以直接播放电视节目。 大部分国产的PDP都是内置电视接收器，如海信、上广电SVA和TCL的多款产品。而国外的厂家，有些产品采用外置电视接收器，也有部分产品采用内置电视接收器。一般把外置电视接收器的PDP称为等离子显示屏，把内置电视接收器的PDP称为等离子电视，选购时应问清楚是否带电视接收功能。 等离子显示屏PDP是一种利用气体放电的显示装置，这种屏幕采用了等离子腔作为发光元件。大量的等离子腔排列在一起构成屏幕。等离子显示屏的屏体是由相距几百微米的两块玻璃板组成，与空气隔绝，每个等离子腔体内部充有氖氙等惰性气体，密封在两层玻璃之间的等离子腔中的气体会产生紫外光，从而激励平板显示屏上的红绿蓝三基色荧光粉发出可见光。每个离子腔体作为一个像素，其工作机理类似普通日光灯。这些像素的明暗和颜色变化组合，产生各种灰度和色彩的图像，而电视彩色图像由各个独立的像素发光综合而成。 编辑本段特点 等离子（PDP）电视与传统的CRT电视机相比，PDP电视机的最突出特点就是“大而薄”，其他的特点还表现在： （1）薄而轻的结构。由于PDP显示模块配身具有薄而轻的特点，决定了显示屏在总体上相应的结构特征，同时显示尺寸的增大也不需要相应地增大屏体的厚度。 （2）宽视角。PDP可以做到和CRT同样宽的视角，上下左右大于160度。而液晶（LCD）在水平方向视角一般为120度左，垂直方向则更少。 （3）防电磁干扰。由于显示原理的差别，来自外界的电磁干扰，如马达、扬声器等，对PDP的图像几乎没有影响。相比之下，CRT受电磁场的干扰要明显得多。 （4）纯平的图像无扭曲。PDP的RGB栅格在平面上呈均匀分布，而在纯平CRT中内表面非平的，会造成典型的枕形失真。并且当画面的局部亮度不均匀时，CRT往往还会产生相应的图像扭曲失真，而PDP就不有这种现象。 （5）没有会聚和聚焦问题。 等离子电视机属于高新尖端的电子产品，对许多顾客来说都是比较陌生的，许多人在使用时都因不了解其原理而小心翼翼的，从而不能完全享受到等离子电视机所带来的享受。其实等离子电视机的使用寿命是普通电视机的两倍左右。如果一台普通电视机的使用寿命是10年，那么等离子就可使用20年左右，并且等离子电视在显示、色彩、外观等许多方面都优于普通电视机，所以等离子电视机是未来电视的发展方向。等离子体维基百科，自由的百科全书
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等离子灯
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等离子灯
等离子体（等离子态，电浆，英文：Plasma）是一种电离的气体，由于存在电离出来的自由电子和带电离子，等离子体具有很高的电导率，与电磁场存在极强的耦合作用。等离子态在宇宙中广泛存在，常被看作物质的第四态（有人也称之为“超气态”）。等离子体由克鲁克斯在1879年发现，“Plasma”这个词，由朗廖尔在1928年最早采用。
目录
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*
*
o 2.1 电离
o
o 2.3 速率分布
* 3 参见
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常见的等离子体
等离子体是存在最广泛的一种物态，目前观测到的宇宙物质中，99%都是等离子体。
* 人造的等离子体
o 荧光灯，霓虹灯灯管中的电离气体
o 核聚变实验中的高温电离气体
o 电焊时产生的高温电弧
* 地球上的等离子体
o 火焰（上部的高温部分）
o 闪电
o 大气层中的电离层
o 极光
* 宇宙空间中的等离子体
o 恒星
o 太阳风
o 行星际物质
o 恒星际物质
o 星云
* 其它等离子体
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等离子体的性质
等离子态常被称为“超气态”，它和气体有很多相似之处，比如：没有确定形状和体积，具有流动性，但等离子也有很多独特的性质。
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电离
等离子体和普通气体的最大区别是它是一种电离气体。由于存在带负电的自由电子和带正电的离子，有很高的电导率，和电磁场的耦合作用也极强：带电粒子可以同电场耦合，带电粒子流可以和磁场耦合。描述等离子体要用到电动力学，并因此发展起来一门叫做磁流体动力学的理论。
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组成粒子
和一般气体不同的是，等离子体包含两到三种不同组成粒子：自由电子，带正电的离子和未电离的原子。这使得我们针对不同的组分定义不同的温度：电子温度和离子温度。轻度电离的等离子体，离子温度一般远低于电子温度，称之为“低温等离子体”。高度电离的等离子体，离子温度和电子温度都很高，称为“高温等离子体”。
相比于一般气体，等离子体组成粒子间的相互作用也大很多。
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速率分布
一般气体的速率分布满足麦克斯韦分布，但等离子体由于与电场的耦合，可能偏离麦克斯韦分布。
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参见
* 等离子体物理学
取自"http://zh.wikipedia.org/wiki/%E7%AD%89%E7%A6%BB%E5%AD%90%E4%BD%93"
Category: 等离子体物理学
Plasma (physics)
From Wikipedia, the free encyclopedia.
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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).
A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation
Enlarge
A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation
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 Ref.
Contents
[hide]
* 1 Common plasmas
* 2 Characteristics
o 2.1 Plasma scaling
o 2.2 Temperatures
o 2.3 Densities
o 2.4 Potentials
* 3 In contrast to the gas phase
* 4 Complex plasma phenomena
* 5 Ultracold Plasmas
* 6 Mathematical descriptions
o 6.1 Fluid
o 6.2 Kinetic
o 6.3 Particle-in-cell
* 7 Fundamental plasma parameters
o 7.1 Frequencies
o 7.2 Lengths
o 7.3 Velocities
o 7.4 Dimensionless
o 7.5 Miscellaneous
* 8 Fields of active research
* 9 See also
* 10 External links
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Common plasmas
A solar coronal mass ejection blasts plasma throughout the Solar System. http://antwrp.gsfc.nasa.gov/apod/ap020516.html Ref &Credit
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A solar coronal mass ejection blasts plasma throughout the Solar System. http://antwrp.gsfc.nasa.gov/apod/ap020516.html Ref &Credit
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
o Inside fluorescent lamps (low energy lighting), neon signs
o Rocket exhaust
o The area in front of a spacecraft's heat shield during reentry into the atmosphere
o Fusion energy research
o The electric arc in an arc lamp or an arc welder
o Plasma ball (sometimes called a plasma sphere or plasma globe)
* Earth plasmas
o Flames (ie. fire)
o Lightning
o The ionosphere
o The polar aurorae
* Space and astrophysical
o The Sun and other stars (which are plasmas heated by nuclear fusion)
o The solar wind
o The Interplanetary medium (the space between the planets)
o The Interstellar medium (the space between star systems)
o The Intergalactic medium (the space between galaxies)
o The Io-Jupiter flux-tube
o Accretion disks
o Interstellar nebulae
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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:
1. Debye screening lengths that are short compared to the physical size of the plasma.
2. Large number of particles within a sphere with a radius of the Debye length.
3. Mean time between collisions usually is long when compared to the period of plasma oscillations.
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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[2]) 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)
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Temperatures
The central electrode of a plasma lamp, showing a glowing blue plasma streaming upwards. The colors are a result of the radiative recombination of electrons and ions and the relaxation of electrons in excited states back to lower energy states. These processes emit light in a spectrum characteristic of the gas being excited.
Enlarge
The central electrode of a plasma lamp, showing a glowing blue plasma streaming upwards. The colors are a result of the radiative recombination of electrons and ions and the relaxation of electrons in excited states back to lower energy states. These processes emit light in a spectrum 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.
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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 n0. In a hot plasma this is small, but may still determine important physics. The degree of ionization is ni / (n0 + ni).
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Potentials
Lightning is an example of plasma present at Earth's surface. Typically, lightning discharges 30 thousand amps, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays [1]. Plasma temperatures in lightning can approach 28,000 kelvins and electron densities may exceed 1024/m3.
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Lightning is an example of plasma present at Earth's surface. Typically, lightning discharges 30 thousand amps, at up to 100 million volts, and emits light, radio waves, x-rays and even gamma rays [1]. Plasma temperatures in lightning can approach 28,000 kelvins and electron densities may exceed 1024/m3.
Since plasmas are very good conductors, electric potentials play an important role. The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the plasma potential or the space potential. If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to 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^{e\Phi/k_BT_e}. Differentiating this relation provides a means to calculate the electric field from the density: \vec{E} = (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.
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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 mattersolid, 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
1. 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.
2. 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.
3. 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.
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Complex plasma phenomena
Tycho's Supernova remnant, a huge ball of expanding plasma. 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
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Tycho's Supernova remnant, a huge ball of expanding plasma. 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, 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.
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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.
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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.
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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.
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Kinetic
For some cases the fluid description is not sufficient. Kinetic models inc
