MadSci Network: Physics

Plasma state.

Area: Physics
Posted By: Mark Bachman, Post-doc/Fellow Physics
Date: Mon Sep 9 12:55:48 1996
Message ID: 841262375.Ph

A plasma is an ionized gas. You may know that matter is made of atoms and that atoms are made of nuclei and electrons. Most of the time, the electrons are "bound" to the nuclei (they stay near them). The attraction between electrons and nuclei is quite strong but sometimes you can pull the electrons away from the atoms. When this happens, we say that the you have "ionized" the atom.

The usual way to create a plasma is to heat a gas to very high temperature (close to 10,000 C). When a gas is heated to very high temperatures the gas atoms bounce against each other so hard that they often knock off each others' electrons, and so ionize each other. When this happens, the gas becomes a plasma. The atoms are still the same elemental atoms, but they are ionized. Sometimes you can create a plasma by dicharging electrons into a gas. A neon light crates a weak plasma this way.

Often physicists refer to a plasma as another "state" of matter. What we mean is that the plasma doesn't behave like a solid, liquid or gas anymore. Although it is most similar to gas, a plasma does things a gas won't. For example, a plasma conducts electricity and a plasma can be moved around using magnets. Plasmas are very hard to put into a bottle since they will either melt the container or react with it and turn back into gas. Usually, physicists use large magnets to hold them.

Plasmas are everywhere. Our earth is surrounded by a plasma called the ionosphere (held in place by the earth's magnetic field), and we get bathed by a plasma from the sun called the "solar wind". Lightning creates plasma in the air (which quickly reacts with the neighboring air to turn back into ordinary gas). Neon and fluorescent lights contain some plasma. Interstallar space contains plasma and the sun is made completely of plasma. In fact, 99% of the mass in the universe is made of plasma!

Neon and fluorescent lamps are useful applications of plasmas. Probably the most important application for plasma is as a way to do nuclear fusion. Physicists try to squeeze plasma into a small volume using powerful magnets. If they can squeeze it together tighly enough and long enough, the atoms (ions) in the plasma might collide hard enough to initate a nuclear reaction called "fusion". When fusion happens, you get a LOT of energy out--much more than burning gas or oil.

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