Nuclear Fusion

• Nuclear fusion is the process in which two lighter nuclei are combined to be fused together to from a heavier and stable nucleus.
• The mass of the product nucleus formed is less than the sum of the masses of the nuclei fused.
• The mass difference or the mass defect is converted into energy according to reaction, △E =
  △m x C². A typical fusion reaction is the formation of a Helium nucleus by fusing four hydrogen atom is as follows.

• The technical problem is the method by which 4 hydrogen nuclei can be fused together since all the four hydrogen nuclei are positively charged and there shall be electrostatic propulsion between them.
• Thus for the fusion reaction to take place, the component nuclei must be brought to within a distance of the order of 10 cm.
• In order to approach so closely, they must be imparted high energies such that they may overcome the repulsive forces between them.
• The only practical way of fusing the nuclei together is to raise their temperature to an excessively high value of the order of (10)^{9 o}C. The reactions that take place at such high temperatures are known as thermo-nuclear reactions.

Plasma Technology :

1. Power generated by nuclear fusion processes is called fusion power.
2. In this, two lighter nuclei are combined to be fused together to form a heavier and stable nucleus usually deuterium and tritium.
3. During this, enormous amount of energy is released due to mass defect during fusion process.
4. Such a process of fusion requires very high temperatures of the order of 150 million degree Celsius.
5. Energy from fusion reaction is used to operate a steam turbine for generation of power.
6. Plasma technology relates to commercial production of net usable power from fusion source.
7. During fusion process, at extreme temperatures, electrons are separated from nuclei these are left in a fluid state known as plasma-a hot and electrically charged gas.
8. The leading design for controlled fusion are :

Use of magnetic confinement :

1. In this the flow of current is induced by external magnetic field to generate a magnetic field around plasma.
2. It creates an inward directed force according to Lenz’s law. It causes the plasma to collapse inwards and raises its density.
3. The denser plasma generates denser magnetic field which generates an increased inward force.
4. This way a chain reaction is set up and produces very high temperatures needed for fusion reaction.

1. Laser confinement of plasma involves the use of technique of implosion of a micro capsule irradiated by laser beams.
2. Experimental results have shown that laser wave length in the range of infrared frequencies were not able to compress the fuel since it lost a large amount of energy before compression.
3. Recent development is to save laser beam energy by using a technique called fast ignition for better confinement of plasma.The research on this technique is under experimental stage.