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What is Plasma?

Atoms, the basic units of matter, consist of a central nucleus surrounded by a cloud of negatively charged electrons. When e.g. an electric field is applied or at high temperatures, these electrons can be separated from the nuclei and gas becomes plasma - an ionized, quasi neutral gas yet containing charged particles. A plasma can be seen as a collection of particles that is (at least partially) charged and is therefore sensitive to electromagnetic forces.

Hydrogen gas , consisting of electrons orbiting protons. Proton and electron plasma.
Hydrogen gas consisting of electrons orbiting protons. Hydrogen plasma, consisting of separate protons and electrons.
Plasma sounds exotic, like a special substance, an abnormal state of matter. But in reality almost all (non-dark) matter in our universe exists in the plasma state. Our sun, the stars that we can see, and even regions of interstellar dust, all consist of plasma.

 

Plasmas can not only be found in the far ends of the cosmos, but also closer to home and even here on earth plasmas can be admired very often. When lightning strikes, a strong current between the clouds and the ground ionizes air molecules. And when particles from the solar wind are excited by the earth's magnetic field lines, they can also form a plasma. When ionized nitrogen atoms from this plasma recombine with an electron, they emit a photon and we can see the beautiful Northern lights.

The most well known example of a plasma is of course the Sun, the source (ultimately) of all energy on Earth. Apart from the naturally occurring plasmas, we can also create them ourselves and use them for lots of purposes: from the first camp fires of our ancestors to prepare food to the industrial plasmas that are used to manufacture microchips. In plasma screens, small plasma discharges produce the colored light that constitute the pixels. We can read our books by light emitted from plasmas in fluorescent light tubes. And of course, one of the most exciting applications of plasma is to induce a fusion reaction. One of the biggest challenges of our time is to confine a hot plasma and turn it into a fusion power plant.