A plasmoid is a coherent structure of plasma and magnetic fields. Plasmoids have been proposed to explain natural phenomena such as

ball lightning Ball lightning is a rare and unexplained phenomenon described as luminescent, spherical objects that vary from pea-sized to several meters in diameter. Though usually associated with thunderstorms, the observed phenomenon is reported to last ...

, magnetic bubbles in the magnetosphere, and objects in cometary tails, in the solar wind, in the solar atmosphere, and in the

heliospheric current sheet The heliospheric current sheet, or interplanetary current sheet, is a surface separating regions of the heliosphere where the interplanetary magnetic field points toward and away from the Sun. A small electrical current with a current density of ...

. Plasmoids produced in the laboratory include

field-reversed configuration A field-reversed configuration (FRC) is a type of plasma device studied as a means of producing nuclear fusion. It confines a plasma on closed magnetic field lines without a central penetration. In an FRC, the plasma has the form of a self-stabl ...

s, spheromaks, and in

dense plasma focus A dense plasma focus (DPF) is a type of plasma generating system originally developed as a fusion power device starting in the early 1960s. The system demonstrated scaling laws that suggested it would not be useful in the commercial power role, a ...

es. The word ''plasmoid'' was coined in 1956 by Winston H. Bostick (1916-1991) to mean a "plasma-magnetic entity":

The plasma is emitted not as an amorphous blob, but in the form of a
torus In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle. If the axis of revolution does not tou ...
. 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 In physics, magnetic pressure is an energy density associated with a magnetic field. In SI units, the energy density P_B of a magnetic field with strength B can be expressed as :P_B = \frac where \mu_0 is the vacuum permeability. Any magnetic fie ...

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. Plasmoids have been formed in discharges with local magnetic field strengths on the order of 16,000 Tesla.

Cosmic applications

Bostick went on to apply his theory of plasmoids to astrophysics phenomena. His 1958 paper, applied plasma similarity transformations to pairs of plasmoids fired from a plasma gun (

device) that interact in such a way as to simulate an early model of galaxy formation.Bostick, W. H.,
What laboratory-produced plasma structures can contribute to the understanding of cosmic structures both large and small
(1986) ''IEEE Transactions on Plasma Science'' (ISSN 0093-3813), vol. PS-14, Dec. 1986, p. 703-717.

Footnotes

{{Reflist, 30em

References

* Bostick, W. H.,
Experimental Study of Plasmoids
, ''Electromagnetic Phenomena in Cosmical Physics'', Proceedings from IAU Symposium no. 6. Edited by Bo Lehnert. International Astronomical Union. Symposium no. 6, Cambridge University Press, p. 87

Plasmoid characteristics

Cosmic applications

See also

Footnotes

References

See also