The
thermonuclear reaction is a fusion reaction in which two lighter nuclei combine to form a single heavier
nucleus by a collision of the two interacting particles with high temperature. During the process large amount of energy is released.
The source of stellar energy is fusion reaction. Fusion reaction is not easy one because positively charged nuclei have repulsion. we want to overcome these electrostatic repulsive force. The reaction is possible when KE of each of the nuclei is large enough to overcome the repulsion. It is possible only at very high temperatures (107 to 109 K).
Controlled thermonuclear fusion reaction occurs stars inner core because of
its strong self gravity. Energy released from hot core is carried outward to cooler surface. The star is stabilised by inward force of gravity and outward force of pressure (pressure-temperature thermostat is maintained).
A.S.Eddington (1926) was formed the equation for stellar structure. It relates the gravitation force in the star (inwards) to progressive change in pressure from its centre (outwards). From his discovery, we can understand that inward gravitational pressure of a star must maintain the outward radiation and gas pressure to remain in equilibrium. The key
role is played by the control of gravity. The large mass of an
astronomical system makes gravity the most important factor in determining its
behaviour.
Controlled thermonuclear reactions
There are two types of thermonuclear fusion.
(i) In an uncontrolled thermonuclear reaction, Energy is released in uncontrolled manner. This kind of reactions give rise to destructive forces. Energy released from this reaction can’t be tapped for any use. Example: Hydrogen bomb
(ii) In controlled thermonuclear reaction, reaction could be controlled to take place more slowly, the
energy released can be used for constructive purposes.
The main problem is to produce a high temperature and a container in which very hot plasma can be contained under
high pressure to initiate a fusion reaction. Any container can melt in the presence of a plasma. Plasma tends to expand at high pressure. We need Gravitational force in stars or magnetic forces in magnetic confinement fusion reactors to act against it.
Fusion power is safe, clean and renewable power. Harnessing fusion power in a controlled way has not yet been achieved. Nowadays, Fusion energy scientists believe that two types of toroidal geometries like tokamaks and stellarators are the leading plasma confinement for future fusion process.
A tokamak is a machine that confines a plasma in donut shape (sometimes called torus) by applying magnetic fields. Stellarators uses very strong electromagnets to generate twisting magnetic fields around the donut shape. Stellarators have advantages over tokamaks. Stellarators need less injected power to sustain the plasma. And also have greater design flexibility. At the same time, these advantages come at the cost of increased complexity particularly for the magnetic field coils.
