Fusion reactors

  • Fusion reactors is increasingly seen as the future of energy security due to following factors
    • Abundance of fuel (Hydrogen in the form of water in oceans)
    • Clean source of energy as it involves no release of carbon dioxide
    • Elimination of risk from nuclear waste
  • 2 main factors to achieve fusion reaction are fuel and conditions for fusion.
  • A typical fusion reactor uses hydrogen as a fuel that is abundant in the water of the oceans.
  • However the main problem in fusion is that the hydrogen nuclei repel each other.
  • The electric repulsion of 2 hydrogen nuclei can be overcome by heating the hydrogen to temperatures of millions of degrees C. This is what happens in a typical hydrogen bomb
  • However the challenge for building a fusion reactor is that such high temperatures leads to high pressure posing the problem of explosion.
  • This problem of explosion is currently being addressed in 3 ways.
    • The first is to make the hydrogen work at a very low density, so the pressure will not get high. This is the approach used in Tokamak approach.
    • The second method is to let the hydrogen explode, but to keep the explosions small. This is done in laser method.
    • The third way to achieve fusion is by keeping the hydrogen cold. This is called cold fusion.



  • ITER is a fusion reactor that works on the basis of Tokamak approach.
  • At such high temperatures, hydrogen gas is in plasma state (electron and nucleus are not bound) and thus difficult for ordinary containers to hold the hydrogen.
  • Thus under Tokamak approach magnets are used to which confines the hydrogen as long as the nuclei are in motion.
  • As a result this method is sometimes called ‘magnetic confinement”.


  • ITER is a fusion reactor launched in 1985.
  • It is located in Saint-Paul-les-Durance in southern France.
  • It is a joint collaboration of 35 countries with the following members China, the European Union, India, Japan, Korea, Russia and the United States.
  • ITER is designed to produce 500 MW of fusion power from 50 MW of input heating power.
  • ITER project is about 65% complete and is expected to be completed by 2025.


  • One way to get fusion without requiring high temperatures is to cancel its electric charge (remember high temperature is required only to overcome the electric repulsion). This is done by making a particle with negative charge stick to the hydrogen nucleus.
  • In this case muon is used. (remember muon is a fermion similar to electron).
  • When a negatively charged muon sticks to a hydrogen (or heavy hydrogen) nucleus, it cancels the proton charge.
  • This electrically neutral nucleus can then get close to another hydrogen nucleus. Then the nuclear force brings the two nuclei together in fusion.

Net Gain at National Ignition Facility: Historic Development in Fusion

  • The main issue with nuclear fusion experiments so far is that the amount of energy required to produce conditions for fusion is much larger than the amount of energy that can be derived from the fusion process.
  • Recently scientists at National Ignition Facility, California have for the 1st time demonstrated net gain function which simply means they have derived more energy from fusion than the energy used to drive fusion.
  • 2.1 megajoules of energy was used to power the experiment. However, the fusion resulted in the production of 2.5 megajoules of energy.(numbers are not important)
  • The experiment was based on the laser method. (world’s largest laser was used for the purpose)
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