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( Plasma physics)
In physical and chemical usage, plasma refers to an ionized gas, in which a certain proportion of electrons are free, rather than being bound to an atom or molecule. The ability of the positive and negative charges to move somewhat independently makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma therefore has properties quite unlike those of solids, liquids or gases and is considered to be a distinct state of matter. Plasma typically takes the form of neutral gas-like clouds (e.g. stars). This state of matter was first identified in a Crookes tube, and so described by Sir William Crookes in 1879 (he called it "radiant matter").[1] The nature of the Crookes tube "cathode ray" matter was subsequently identified by British physicist Sir J.J. Thomson in 1897,[2] and dubbed "plasma" by Irving Langmuir in 1928,[3] perhaps because it reminded him of a blood plasma.[4] 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. We shall use the name plasma to describe this region containing balanced charges of ions and electrons."[3] Plasmas are by far the most common phase of matter in the universe, both by mass and by volume.[5] All the stars are made of plasma, and even the space between the stars is filled with a plasma, albeit a very sparse one (See astrophysical plasma, interstellar medium and intergalactic space). 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. 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).
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