I recently gave a talk to the student branch of AIAA on my research and plasma applications. I always thought plasmas were cool and useful. Putting together the presentation only reinforced by belief. There are two broad types of plasmas, high-temperature thermal plasmas, and low-temperature non-thermal plasmas. Examples of the former include lighting, arc welding, fusion, the sun. So not very useful for most things. The latter type, non-thermal plasmas however has lot of uses. But first lets talk about what makes up a plasma and why they can be useful.
Plasma is basically a gas with a large fraction of charged particles, usually positive ions and negative electrons. For example an argon plasma may have 80% of the total number of particles as ions, and a corresponding number of electrons. An ion is simply a neutral atom that has been stripped of one or more electrons. So for every ion, a free electron is also created. For the most part the ion has similar properties as the original atom, however because it has a positive charge, the ion, and electrons, will respond to electric and magnetic fields. Thus we can control the behavior of a plasma with externally applied fields, for example to accelerate the charged particles.
This can be used to give the charged particles more energy, so that when they collide with other particles, they can cause reactions. That is one of the primary use of plasmas: to promote or cause chemical reactions. This is the basis of plasma processing and etching that is used to create semiconductors which go into all electronics. It is also used to create high temperature coatings for engines, and water shedding coatings for clothing. The collision of energetic ions can also release light. This is the basis for much of our lighting technology today such as florescence lights in buildings and HID lamps in stadium lights and car headlights.
On the less common end, plasma is also used for space satellite propulsion, to create fusion here on Earth, control air flow on airplane wings, or used to remove plaque on teeth. In fact plasma is the most common form of matter in the universe. It makes up about 99% of the visible matter in the universe, most of it in the form of ions and electrons in the space between planets, stars, and galaxies. Our Sun, and stars in general, exist through inertial fusion of hydrogen and helium ions, i.e. plasmas. So plasmas are ever present, allow life to exist on Earth, and make civilization better.