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Plasmoid
A plasmoid is a coherent structure of plasma and magnetic fields. Plasmoids have been proposed to explain natural phenomena such as ball lightning, magnetic bubbles in the magnetosphere,〔Hones, E. W., Jr., "The magnetotail - Its generation and dissipation", (1976) ''Physics of solar planetary environments''; ''Proceedings of the International Symposium on Solar-Terrestrial Physics'', Boulder, Colo., June 7–18, 1976. Volume 2.〕 and objects in cometary tails,〔Roosen, R. G.; Brandt, J. C., "Possible Detection of Colliding Plasmoids in the Tail of Comet Kohoutek" (1976), ''Study of Comets'', Proceedings of IAU Colloq. 25, held in Greenbelt, MD, 28 October - 1 November 1974. Edited by B. D. Donn, M. Mumma, W. Jackson, M. A'Hearn, and R. Harrington. National Aeronautics and Space Administration SP 393, 1976., p.378〕 in the solar wind,〔Lemaire, J.; Roth, M., (Differences between solar wind plasmoids and ideal magnetohydrodynamic filaments ) ''Planetary and Space Science'', Volume 29, Issue 8, p. 843-849〕〔Wang, S.; Lee, L. C.; Wei, C. Q.; Akasofu, S.-I., A mechanism for the formation of plasmoids and kink waves in the heliospheric current sheet (1988) ''Solar Physics'' (ISSN 0038-0938), vol. 117, no. 1, 1988, p. 157-169.〕 in the solar atmosphere,〔Cargill, P. J.; Pneuman, G. W., "(The energy balance of plasmoids in the solar atmosphere )" (1986), ''Astrophysical Journal'', Part 1 (ISSN 0004-637X), vol. 307, Aug. 15, 1986, p. 820-825.〕 and in the heliospheric current sheet. Plasmoids produced in the laboratory include field-reversed configurations, spheromaks, and in dense plasma focuses.
The word ''plasmoid'' was coined in 1956 by Winston H. Bostick (1916-1991) to mean a "plasma-magnetic entity":〔Bostick, Winston H., "(Experimental Study of Ionized Matter Projected across a Magnetic Field )", (1956) ''Physical Review'', vol. 104, Issue 2, pp. 292-299〕
The plasma is emitted not as an amorphous blob, but in the form of a torus. We shall take the liberty of calling this toroidal structure a plasmoid, a word which means plasma-magnetic entity. The word plasmoid will be employed as a generic term for all plasma-magnetic entities.
==Plasmoid characteristics==
Bostick wrote:〔
Plasmoids appear to be plasma cylinders elongated in the direction of the magnetic field. Plasmoids possess a measurable magnetic moment, a measurable translational speed, a transverse electric field, and a measurable size. Plasmoids can interact with each other, seemingly by reflecting off one another. Their orbits can also be made to curve toward one another. Plasmoids can be made to spiral to a stop if projected into a gas at about 10−3 mm Hg pressure. Plasmoids can also be made to smash each other into fragments. There is some scant evidence to support the hypothesis that they undergo fission and possess spin.
A plasmoid has an internal pressure stemming from both the gas pressure of the plasma and the magnetic pressure of the field. To maintain an approximately static plasmoid radius, this pressure must be balanced by an external confining pressure. In a field-free vacuum, for example, a plasmoid will rapidly expand and dissipate.
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