How is Plasma Formed?
In principle, plasma can be formed by providing energy to the substance (e.g., heating). With energy, the phase of the substance will change from solid to gas. If sufficient energy is further added to the gas, a molecular gas will gradually dissociate into an atomic gas due to the thermal kinetic energy of the particles exceeding the molecular binding energy (Figure 1). As a result, ionized gas or plasma is formed. Other energy forms such as the application of electric field to gases, chemical reactions such as in flames, fusion reactions in stars, adiabatic gas compression, etc. can also form plasma.
Types of Plasma
Plasmas are usually classified as non-equilibrium and equilibrium plasma. In equilibrium plasma, the neutral and heavy species (atoms, molecules) are at a lower temperature closer to the surrounding temperatures (atmosphere, furnace, etc.). However, the lighter electrons are at a much higher temperature of ~10,000 K to 40,000 K. This means that the electrons have a higher average speed (energies) than if they were at surrounding temperatures. Non-equilibrium plasmas are usually achieved by the application of electric fields that accelerate the electrons to high energies. Figure 2 shows a non-equilibrium plasma reactor sustained by AC electrical discharge at ACT. In equilibrium plasmas, the temperatures of the neutral species and electrons are closer to each other. These types of plasmas are observed in stars, high current intense arc welding etc.
Figure 2. A plasma Reactor at ACT.
What is Plasma Used For?
- Chemical synthesis using renewable energy
- Plasma-assisted combustion
- Greenhouse gas mitigation
- Semiconductor manufacturing
- Surface treatment
- Biological applications
- Food engineering
- Toxic air treatment
- Nanomaterial synthesis
- Electrochemistry etc. and the applications will continue to grow in the coming years.
Plasma-related technology development
ACT has been heavily involved in two plasma-related technology developments:
J.A. Bittencourt, Fundamentals of Plasma Physics, 3rd Edition, Springer (2004).
F. Chen, Introduction to Plasma Physics and Controlled Fusion, 2nd Edition, Vol. 1, Plenum Press, New York and London (1984).