![]() ![]() The plasma approximation: Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just the interacting with the closest particle (these collective effects are a distinguishing feature of a plasma).We explain these parameters, and then describe how plasmas interact with electric and magnetic fields and outline the qualitative differences between plasmas and gases.Īlthough a plasma is loosely described as an electrically neutral medium of positive and negative particles, a more rigorous definition requires three criteria to be satisfied: Some of the most important plasma parameters are the degree of ionization, the plasma temperature, the density and the magnetic field in the plasma region. Plasma properties are strongly dependent on the bulk (or average) parameters. The faint yellow area shown above the north pole represents gas lost from Earth into space the green area is the aurora borealis-or plasma energy pouring back into the atmosphere. The Earth's " plasma fountain", showing oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. (which are plasmas heated by nuclear fusion) ![]() Plasma used to etch dielectric layers in the production of integrated circuits.Plasma ball (sometimes called a plasma sphere or plasma globe).The electric arc in an arc lamp, an arc welder or plasma torch.The area in front of a spacecraft's heat shield during reentry into the atmosphere.Inside fluorescent lamps (low energy lighting), neon signs.Notable plasma physicist Hannes Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of plasma (see dusty plasmas). 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. Since the space between the stars is filled with a plasma, albeit a very sparse one (see interstellar medium and intergalactic space), essentially the entire volume of the universe is plasma (see astrophysical plasmas). Some estimates suggest that up to 99% of the entire visible universe is plasma. Plasmas are the most common phase of matter. They are typically formed by heating and ionizing a gas, stripping electrons away from atoms, thereby enabling the positive and negative charges to move freely. Plasma typically takes the form of neutral gas-like clouds or charged ion beams, but may also include dust and grains (called dusty plasmas). We shall use the name plasma to describe this region containing balanced charges of ions and electrons." Langmuir wrote: "Except near the electrodes, where there are sheaths containing very few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. Thomson in 1897, and dubbed "plasma" by Irving Langmuir in 1928, perhaps because it reminded him of a blood plasma. ![]() The nature of the Crookes tube " cathode ray" matter was subsequently identified by British physicist Sir J.J. This fourth state of matter was first identified in a discharge tube (or Crookes tube), and so described by Sir William Crookes in 1879 (he called it "radiant matter"). The free electric charges make the plasma electrically conductive so that it responds strongly to electromagnetic fields. " Ionized" means that at least one electron has been dissociated from a proportion of the atoms or molecules. In physics and chemistry, a plasma is typically an ionized gas, and is usually considered to be a distinct phase of matter in contrast to solids, liquids, and gases because of its unique properties. These processes emit light in a spectrum characteristic of the gas being excited. The colors are a result of the relaxation of electrons in excited states to lower energy states after they have recombined with ions. ![]() A plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation. ![]()
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