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What is Plasma?

A plasma is a gas, but it is an unusual kind of gas. In a normal gas, the atoms or molecules are electrically neutral, but in a plasma at least some of these particles have either lost or gained an electron, so that a plasma consists of free electrons and positively or negatively charged atoms and molecules known as ions. A high temperature must be reached before a normal gas can be transformed into a plasma. The lowest temperature at which plasma can usually be seen is a few tens of thousands of degrees, but many plasmas are much hotter than this: Plasmas can reach temperatures of hundreds of thousands or even millions of degrees. Relatively cool plasmas usually have a distinctive luminous colour that depends on the gas in which the plasma is formed.

The image on the left is a hydrogen plasma confined by a magnetic field in the START device, formerly operated by UKAEA fusion at their Culham Laboratory near Oxford, England. This is a fairly typical laboratory plasma. It is about 1 metre across, and it has a temperature of perhaps 100 000 K.

Potentially one of the most important applications of plasma is as a source of fusion energy. The hottest plasmas are so hot that nuclear reactions can occur within them. Certain types of atoms with light nucleii, such as special heavy isotopes of hydrogen, can be induced to combine into heavier nucleii under these conditions. The release of energy when this happens is considerable, and could be an important source of power for electricity generation, for example. It is very hard to make a plasma hot enough and durable enough to produce a significant amount of fusion power, but the progress that has been made by experiments such as JET is impressive.

This is the interior of the Joint European Torus (JET), located near Oxford, England, and one of the largest plasma physics experiments in the world. JET has demonstrated that artificial nuclear fusion can be produced in a hot enough plasma. Notice the size of the man at bottom right!

There are many other applications of plasmas with enormous economic importance. For example, plasmas are widely used in the semiconductor device manufacturing industry. Cheap modern microchips could not be made without plasma aided manufacturing. Plasmas are also used for applying high performance coatings for engineering and medical applications.

This is a plasma in argon gas at a pressure of about one thousandth of an atmosphere, with the temperature of the plasma electrons about thirty thousand degrees. Plasmas like this are used for processing semiconductor materials. The lobes that can be seen here are an undesirable instability, which is being studied in NCPST.

NCPST is active in a wide variety of research areas, ranging from basic studies of plasma to fusion technology development to plasma-aided manufacturing.