Why is Plasma interesting?

Plasma is the most common phase of matter in the visible universe, even if it almost doesn’t exist naturally on the earth. 

What’s plasma?

Everything is composed by particles called atoms. An atom consists of a dense nucleus of positively charged protons and electrically neutral neutrons, surrounded by a large electron cloud consisting of negatively charged electrons turning around the nucleus.

Composition of an atom

An atom is electrically neutral if it has the same number of protons as electrons. An atom which has lost or gained electrons, making it positively or negatively charged is called an ion.

When atoms are closely packed together, the state of the matter is solid. When atoms can slide on each other: the state of matter is liquid. A liquid takes the shape of its container. The state of matter obtained when atoms are freely moving is gas.

Plasma is the state of matter obtained when elements of atoms are separated.

To pass from a gas to a plasma you need to ionize matter: increasing temperature (eating a gas at very high temperature) or with an external source of particles bombarding the gas (example: ionosphere ionized by solar radiations). Electrons can be tired away from atoms. Plasma is thus a globally neutral mix of charged particles, electrons and ions.

Characteristics of plasma

To characterize plasma, 2 principal parameters are electron density and temperature.

Electron density: It’s the number of free electrons per unit volume.

Temperature: measure of the thermal kinetic energy per particle. It’s measured in kelvins or electron volts

Range of plasma

Can we find natural plasma on the earth?

Natural terrestrial plasma phenomena are rare, but they exist. Following examples are the most common.

Lightening	Polar auroras	Ionosphere (uppermost part of the atmosphere)

Light from plasma phenomena comes from the excitation of atoms. Atoms are exited by the ionization: when they pass in an unexcited state, they emit a photon which is light.

Can we find natural plasma in the universe?

Plasma composes 99% of universe. Here are examples following.