When the plasma parameter, the number of charge carriers within the Debye sphere, is substantially greater than unity, the plasma approximation is used. This requirement is easily demonstrated to be comparable to the ratio of plasma electrostatic and thermal energy densities being minimal. Weakly linked inline plasma are such plasmas.
Plasma is one of the four fundamental states of matter (from the Ancient Greek (plásma)'moldable substance'). It contains a large number of charged particles, such as ions and/or electrons. Plasma is distinguished from the other fundamental states of matter by the existence of charged particles. It's the most common type of ordinary stuff in the universe, and it's usually connected with stars like the Sun. It can be found in the rarefied intracluster medium as well as possibly intergalactic regions. Heating a neutral gas or exposing it to a strong electromagnetic field can be used to create plasma.
Plasma is electrically conductive due to the existence of charged particles, with individual particle dynamics and macroscopic plasma motion driven by collective electromagnetic fields and extremely sensitive to externally imposed fields.
Many modern technological systems, such as plasma televisions and plasma etching, rely on plasma's reactivity to electromagnetic fields.
A certain proportion of neutral particles may also be present, depending on temperature and density, in which case plasma is referred to as partially ionised. Partially ionised plasmas include neon signs and lightning. The transition to plasma, unlike the phase transitions between the other three states of matter, is not well defined and is a question of interpretation and context. It is debatable if a certain level of ionisation is sufficient to term a substance "plasma."
Sir William Crookes was the first to identify plasma in a laboratory setting. Crookes gave a speech to the British Association for the Advancement of Science in Sheffield on Friday, August 22, 1879, about "radiant matter." The research of Irving Langmuir and his colleagues in the 1920s was the first systematic study of plasma. In 1928, Langmuir also coined the term "plasma" to describe ionised gas.
Except near the electrodes, where there are sheaths containing very few electrons, the ionised gas has roughly equal amounts of ions and electrons, resulting in a very modest space charge. This zone holding balanced charges of ions and electrons will be referred to as plasma.
Langmuir first used the word by analogy with blood plasma, according to Lewi Tonks and Harold Mott-Smith, both of whom worked with him in the 1920s. The transmission of electrons from thermionic filaments, according to Mott-Smith, reminded Langmuir of "the way blood plasma conveys red and white corpuscles and germs."
After solid, liquid, and gas, plasma is the fourth state of matter. An ionised substance becomes highly electrically conductive to the point where long-range electric and magnetic forces dominate its behaviour.
Plasma is a medium containing unbound positive and negative particles that is electrically quasineutral (i.e. the overall charge of a plasma is roughly zero). These particles are unbound, but they are not "free" in the sense that they are not subject to forces. Electric currents are generated by moving charged particles, and any movement of a charged plasma particle influences and is impacted by the fields formed by other charges. As a result, collective behaviour with a wide range of degrees of variation is governed.
Plasma is a state of matter that is unique from the other states of matter. Even though it is comparable to the gas phase in that neither assumes a fixed shape or volume, defining a low-density plasma as merely a "ionised gas" is incorrect and misleading. The table below outlines some of the most significant differences.
The strength and range of the electric force and the good conductivity of plasmas usually ensure that the densities of positive and negative charges in any sizeable region are equal ("quasineutrality"). A plasma with a significant excess of charge density, or, in the extreme case, is composed of a single species, is called a non-neutral plasma. In such a plasma, electric fields play a dominant role. Examples are charged particle beams, an electron cloud in a Penning trap and positron plasmas.
The thermal kinetic energy per particle is measured by plasma temperature, which is generally expressed in kelvin or electronvolts. To maintain ionisation, which is a defining property of a plasma, high temperatures are normally required. The electron temperature in relation to the ionisation energy determines the degree of plasma ionisation (and more weakly by the density). The Saha equation describes the relationship in thermal equilibrium. Ions and electrons tend to recombine into bound states—atoms[33]—at low temperatures, and the plasma eventually becomes a gas.
In most cases, the electrons and heavy plasma particles (ions and neutral atoms) separately have a relatively well-defined temperature; that is, their energy distribution function is close to a Maxwellian even in the presence of strong electric or magnetic fields. However, because of the large difference in mass between electrons and ions, their temperatures may be different, sometimes significantly so. This is especially common in weakly ionized technological plasmas, where the ions are often near the ambient temperature while electrons reach thousands of kelvin. The opposite case is the z-pinch plasma where the ion temperature may exceed that of electrons.Read More
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