Plasma and its Applications

Textbooks at the high school level often refer to Plasma as the fourth state of matter after solid, liquid and gas; but not many are aware that it is the most abundant form of matter in the universe. It might seem to be scarcely available on Earth, but the truth is that the forms of matter we are familiar with were formed from plasma. Therefore, one can say that plasma is our ancestor.

Plasma is a collection of electrical particles viz. electrons and protons/ions. When a gas is heated to sufficient temperatures, the electrons become free and thus result in a collection of free electrons and protons/ions. One can say that plasma is an ionized gas (Note- plasma is not gas, it is just an analogy). Plasma is electrically neutral since no extra charge is introduced to or taken out from the collection. Due to the presence of charged particles, electric and magnetic forces influence the behaviour of plasma. Thus, it exists as a conducting fluid (imagine a soup, not of tomato or corn, but of ions!). Its not easy to make plasma, because very high energy (and correspondingly a high temperature) is required to rip the electrons out of the nucleus. Another way of doing this is by internally heating the gas, i.e. applying high voltage across the gas so that all electrons are accelerated and so are removed. But here as well, the temperature is raised to very high levels. And we, on Earth, do not have containers that can withstand such high temperatures. Therefore, production and confinement of plasma is a huge problem.

Over the years, scientists who worked on magnetohydrodynamics (recall that plasma acts like a fluid) proposed simple models of magnetic confinement of plasma (refer slide 14). Around the same time, with the help of Einstein’s mass-energy equivalence principle, nuclear fission reactors were developed. Einstein’s equation also explained the mechanism of energy production in the Sun- nuclear fusion reaction. The energy obtained from fusion reaction is estimated to be tremendous compared to that of fission reaction. In order for the reaction to happen, a large amount of energy is required to overcome the repulsion of the positively charged nuclei. The sun’s temperature is very high; therefore, the hydrogen nuclei have sufficient energy to fuse. On earth, however, due to container constraints, it is not possible to confine the high energy particles. In order to make fusion energy possible, scientists have come up with plasma confinement chamber, the toroidal magnetic confinement chamber, TOKAMAK. It has toroidal chamber, and magnetic field is applied to the nuclear fuel. Due to the magnetic field, the fusion reactants do not come in contact with the walls of the chamber, and the forces keep it contained inside the chamber (refer slides). The fuel used is a mixture of deuterium and tritium, which undergo fusion to produce energetic neutron, alpha particle and a lot of energy. The energy is further used for other purposes. The waste consists of ashes (small quantity) of helium nuclei. Occasionally, energetic neutrons are also injected so that the reactants are activated. A small quantity of fusion fuel can thus produce a large amount of energy. Its is more eco friendly as compared to fission as the wastes are usually in the form of ash. If we can make this in a controlled way, our energy requirements would be easily taken care of, since we have a lot of fuel (deuterium and tritium) stores in our seas!

Apart from nuclear energy, plasma also plays a major role in other walks of life such as medicinal, environmental as well as in industrial fields. Medicinal uses utilize cold plasma. Plasma which is hot enough to kill pathogens but cold enough to not harm the animal tissue is termed as cold plasma. Its temperature ranges from few tens to hundreds of kelvins. Now you may ask- how come at such low temperatures can we make plasma? The cold plasma is formed at high pressures, therefore at relatively lower temperatures, we can make use of plasma. Also, plasma treatment can affect the texture of surface by interaction of ions with the surface. This is used to manipulate the surface of interest and make better use of it. Even fabrication of chips uses plasma. It is observed that plasma treatment on plant tissues enhances their life. Therefore, plasma covers a wide range of fields. If we realise its invaluable applications and use it in a wise manner, we can be sure of making the world, a better place to live.

by Sai Kaarthik

REFERENCES:

1. www.plasmacoalation.org

2. www.wikipedia.com

• Magnetic confinement of plasma

• ITER

• Cold plasma

3. Concepts of modern physics by Arthur Beiser

4. Encyclopaedia Britannica: Articles on plasma physics