110. Plasma

Plasma in a glowing discharge.

In the positive column of the glowing discharge the concentrations of electrons and ions are almost the same.

The gas containing in equal concentration free electrons and positively charged ions, i.e. in general electrically neutral, is called electron-ion plasma.

If the gas has neutral particles along with charged ones, it is called partially ionized plasma. The positive column of glowing discharge is a partially ionized plasma. Partially ionized plasma is also the upper atmosphere - the ionosphere.

If the degree of ionization is \(\,100%\), then the plasma is called fully ionized.

Plasma in solid objects.

An example of fully ionized plasma are metals. In contrast to gas plasma in solid metals positively charged ions cannot move through the entire volume of the metal. In this respect, plasma of liquid metals is the closest to gas plasma.

Plasma in space bodies.

Due to the high temperature and the action of various ionizers, the atoms of chemical elements in stars ( for instance, in the Sun) are ionized and therefore the star substance can be considered as plasma.

However, plasma is not only made up of stars. In the interstellar medium there are also charged particles (electrons, atomic nuclei), although their density is very low. Therefore, even a very rarefied interstellar medium is a kind of plasma. Unlike hot plasma from stars, the interstellar plasma temperature is very low.

Maintaining a high temperature in stars and therefore the very existence of plasma in them requires huge amounts of energy. This energy is generated by nuclear reactions inside stars - thermonuclear reactions.

Intensive research is currently under way on the possibility of controlled thermonuclear reactions in Earth conditions. The solution of this problem will give in human hands practically unlimited source of energy.