WHAT IS A PLASMA?

A plasma is basically a state of matter in which electrons are dissociated from their original partners (nuclei, molecules, etc.), giving rise to a collection of charged particles of both signs, that interact strongly. The most usual plasma is a gas in which, through an energy input, the electrons are dissociated from the nuclei. The energy may come from heating the gas or from accelerated electrons in an electric potential that cross the gas. In the first case one has a hot thermal plasma while the second produces a cold plasma. Since a temperature rise above several thousand degrees converts a gas into a plasma, this is often called the fourth state of matter.

WHERE DO WE FIND PLASMAS?

Plasmas in nature are rarely seen over the surface of the Earth. They are formed in lightnig during storms, for instance, and are ephemeral. However, as soon as we leave the surface of the Earth they are found almost everywhere: In the upper atmosphere, called ionosphere; whithin the outer Earth's magnetic field lines, called magnetosphere; in the interplanetary space; in the Sun and all other stars, in the interstellar medium, etc., etc. The plasmas we have on the Earth are man-made plasmas. The most familiar are those in fluorescent lamps, but the most impresive are created in the experimental machines used for Nuclear Fusion Research. These have temperatures in excess of ten million degrees. Plasmas are also used for different technological applications like film deposition, surface hardening, or in flat computer displays.

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