Controlled Thermonuclear Fusion

Fusion is the main source of energy in stars. In stars, extremely high temperature and pressure allow light nuclei to combine and release energy.

Scientists aim to reproduce this process on Earth in a controlled form. This is called controlled thermonuclear fusion.

Controlled thermonuclear fusion is the attempt to produce this fusion process under controlled conditions on Earth so that the released energy can be used safely and continuously.

Light nuclei release energy when they combine because the resulting nucleus is more stable. This is related to nuclear binding energy, where a more tightly bound nucleus has lower mass-energy than the separate lighter nuclei.

In nuclear reactions, a small loss of mass appears as energy according to mass-energy equivalence. This is the basic reason why fusion can produce enormous energy.

For controlled fusion to occur, the following conditions are necessary:

• Very high temperature: about 10⁸ K is required for nuclei to come close enough to fuse.
• Ionised state of matter: at such high temperatures, matter exists as plasma containing free nuclei and electrons.
• Proper confinement: the hot plasma must be contained long enough for fusion to occur.
• Sufficient density and time: fusion is effective only if enough particles interact for long enough.

1. Are nuclear reactions balanced like chemical reactions?

• Yes, but in a different way. Chemical reactions conserve the number of atoms of each element, whereas nuclear reactions conserve the total number of protons and neutrons, even when one element changes into another.

2. How is mass converted into energy if protons and neutrons are conserved?

• The total number of protons and neutrons remains the same, but the binding energy of the nuclei changes. This change causes a mass defect, and the lost mass is converted into energy according to E = mc².

3. Does mass–energy conversion occur only in nuclear reactions?

• No. It also occurs in chemical reactions, but the mass change is extremely small—about a million times smaller than in nuclear reactions—so it is usually impossible to detect.

Conclusion:
Nuclear reactions conserve the numbers of protons and neutrons while converting small amounts of mass into large amounts of energy. Chemical reactions also involve mass–energy conversion, but the effect is negligible.