Humans always have curiosity about the sun. We always wonder from where the sun is getting so much energy that it is supplying the whole solar system for billions of years. There must be some continuous process which is going on inside the sun and supplying so much of energy whether in the form of light and heat. So the answer is that there is a reaction which is going on from billions of years inside the sun which is called Thermonuclear fusion.
In this process, two or more atomic nuclei combine or fuse to form two or more than two heavier atomic nuclei and subatomic particles like neutrons or protons under the extreme high temperature.
Now the question remains: how can you say that the combination of two or more nuclei will lead to the liberation of this much energy. So the answer to this is that the subatomic particles like neutrons and protons are attracted toward each other by binding energy called nuclear binding energy. So when the nuclei fuses then the binding energy gets changed before and after thermonuclear fusion. This leads to the difference in mass before and after the fucion and this mass will be responsible for liberation of energy by the formula given as –
$\mathrm{\Rightarrow\: E\:=\: mc^{2}}$
Where E = Energy liberated, m = difference in mass before and after reaction and c = speed of light.
Now this process is continuous inside the sun where the hydrogen gasses are combined to form Helium gas and liberate the energy under the extreme high temperature. So we can use the same process to generate the energy on our earth to produce electricity or for various other work. Is it possible to do so? The answer is yes but in a controlled manner. It means that the thermonuclear fusion occurring inside the sun is not controllable and we cannot do this on earth because it will produce extreme energy and which may cause destruction.
One of the best example of uncontrolled thermonuclear fusion is the Hydrogen bomb which is highly destructive. So the term Controlled Thermonuclear Fusion comes into picture. Under this we will try to use the thermonuclear fusion for constructive usage. Now in this tutorial we will try to understand the basics required for the controlled thermonuclear fusion.
Now as we know that the amount of energy liberated in the thermonuclear fusion is very high so we need to do the process in such a way that it does not affect the outer world. So the main issue is the confinement of hot plasma.
Now what is hot plasma? Since the very high temperature is produced in thermonuclear fusion which causes the ionization of the gasses which is called Plasma. Now this plasma cannot come in direct contact with any material because no material can sustain that much temperature. So it must be located in a vacuum. So at high pressure, the plasma needs some external force which can prevent it from expanding. These forces may be Gravitational force which prevents the expansion of star or sun and magnetic force in magnetic confinement thermonuclear fusion reactors, inertial confinement and Electrostatic confinement which is used for confining the ions.
Let us understand Gravitational and magnetic confinement in detail.
In Gravitational confinement the amount of mass plays a very important role. It can happen in such a body which is so giant like stars. So the stars are fulfilling the criteria of mass. In stars when there is no hydrogen left (Heaviest stars having mass equals to 8-10 times of Solar mass) in the core and all gets converted in Helium then the Helium starts fusing in Carbon. This process will continue and some of these nuclei fuse to iron nuclei which have the highest binding energy.
As we know that the electrically charged particles follow the magnetic field lines for their path of trajectory. Same will apply for the ionized fuel, they will also follow the magnetic field lines and get trapped in that and this form confinement.
Q1. What is Nuclear fusion?
Ans: It is the process of combination of two or more atomic nuclei to form two or more heavier nuclei, subatomic particles and a lot of energy.
Q2. What type of nuclear fusion will undergo in the Sun?
Ans: Uncontrolled Nuclear fusion will undergon inside any star of this universe. So in the sun, it is uncontrolled nuclear fusion which is producing heat and light energy.
Q3. What are the cons of Uncontrolled Thermonuclear fusion?
Ans: The cons of Uncontrolled Thermonuclear fusion are -
a) The amount of energy liberated is so high that it will cause destruction rather than any useful work. For example - Hydrogen Bomb
b) In uncontrolled thermonuclear reactions, the conditions are very unpredictable. So we cannot stop or predict it for any constructive usage.
Q4. What is the major problem for using controlled thermonuclear fusion for constructive use?
Ans: One of the major problems is the confinement of hot plasma in the controlled thermonuclear fusion. Because the temperature is so high in this case that no material can withstand the temperature.
Q5. What is the condition for Gravitational confinement?
Ans: One of the major conditions is that the mass of the object should be very high and it should be approx. 8-10 times the solar mass.
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