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Plasma basics

In 1879 Sir William Crookes, an English Physicist identified a fourth state of matter, now known as plasma. Less famous than the three other states it is however the most common, making up over 99% of the visible universe. Plasmas can in effect be though of as the next stage of matter after a gas; a gas being composed of free moving molecules with no electronic charge, while a plasma is made up of free moving electrons and ions, with negative and positive charges respectively.

Although plasmas are similar in many ways to gases they display a number of unique properties such as the ability to conduct electricity, due to their charged particles. Plasmas technology represents an exciting and rapidly expanding area of research encompassing many scientific disciplines. Already plasma technology has a number of applications in the following areas, Nuclear Fusion, Lighting and high intensity lamps, Surface treatment of materials, Lasers, Sterilization of medical equipment, Propulsion, Material analysis, Flat panel displays and the next generation of flat screen plasma televisions as well as many more, mundane everyday items!

Recent interest in plasma technology has focused increasingly on the area of ‘dusty or complex plasmas, indeed this field has been on of the fastest growing areas of physics research in recent years. Ordinary plasma represents an interesting state of matter, just like fluid, solid and gas, however many of the technical applications of plasma use complex or dusty plasmas

Complex plasma represents a general term for plasmas that have been enriched with small nano or micro sized particles; the presence of these particles, one hundred billion times larger than the charged ions that make up the plasma, leads to complex plasmas having a different and more diverse series of properties and uses than ordinary plasmas. Dusty plasmas are a type of complex plasma containing dust particles, common throughout space, in such areas as the rings of Saturn and parts of the Eagle nebullar as well as many more.

A dusty plasma consists of two types of particle, the first are the sub atomic charge carrying ions and electrons that are present in normal plasma, the second are the larger (macroscopic) grains that initially have no particular charge. However over time, due to the mobility of the plasmas electrons, negative charge collects on the surface of the larger grains, and they become in effect charge carriers. Due to this, the spread of grains in the plasma has a huge effect on the spread of charge, with parts of the plasma that have a high density of grains becoming mostly negative and parts with a low density of grains being mostly positive.

Dusty plasmas are a more suitable model for plasma research for a number of reasons; firstly theirmacroscopic component can be visualized easily, allowing research at the most fundamental (kinetic) level for the first time ever.   Secondly the plasma movement is slowed down, and therefore the physics is observable in ‘slow motion’; and thirdly liquid and crystalline plasma states can be investigated.

The basics of dusty plasma dynamics and the way in which these unique states of matter form has massive implications in the sense that a better understanding of plasmas could lead to advancements in almost all fields of science, with huge benefits in everything from drug design to cleaner cheaper energy. Additionally the part played by dusty plasmas in the birth of stars and entire universes is some thing that could help us understand the birth of the earth and possibly even life itself; if a substa nce is believed to make up over 99% of the universe it seems pretty important that we underst and it.

Research is currently being carried out all over the world to help us understand dusty plasmas, however this research is hindered by gravity. Over time gravity causes sedimentation with the larger ‘grains’ settling towards the bottom of any plasma, additionally gravity creates convecti on currents that affect the movement of the plasma. On earth there is no way we can switch off gravity, and until we can do this our ability to study plasmas is severely restricted; for this reas on the future of plasma research seems to be in space, where the problem of gravity is removed

Due to the need for a microgravity plasma research facility, the European Space Agency (ESA) set-up the International Microgravity Plasma Facility (IMPF), which its hoped will bring together the best minds from around the world and provide them with the facilities required to develop a better understanding of plasma dynamics. Eventually it is hoped the IMPF will become a permanent and important research tool aboard the International Space Station and will lead to developments in plasma technology and understanding that would not have been possible on earth.