Signing of a Cooperation Agreement between the IAEA and ITER Organization. In the photo, Yury Sokolov, Deputy Director General of the IAEA (left), and Kaname Ikeda, Director General of the ITER Organization (right). (22nd IAEA Fusion Energy Conference, Geneva, Switzerland, 13 October 2008). 
Fusion, a form of nuclear energy generated when light-weight atoms fuse, is the process at work in every star's core, releasing an enormous amount of energy. Researchers have been trying to harness fusion and reproduce it on earth in a controlled manner. If they succeed, they will provide the world a safe, sustainable, environmentally responsible and abundant source of energy.
For decades, the scientific community has been pursuing nuclear fusion, yet now research has reached a critical stage, as scientists are building an experimental reactor that one day may demonstrate that fusion can be used commercially to create electrical power.
What is Fusion?
For more than 50 years, energy has been generated in nuclear power plants through fission, a process in which heavy elements such as uranium are bombarded by neutrons releasing heat in the process.
Nuclear fusion, on the other hand, is based on the opposite principle. In fusion reactors, light atomic nuclei are compressed under intense pressure and heat to form heavier ones and release energy in the process. The process must be optimized to generate more energy than it consumes. With a sufficiently large and sustainable energy 'profit', fusion could be utilized to generate electricity commercially.
The main fuels used in nuclear fusion are deuterium and tritium, both heavy isotopes of hydrogen. Deuterium constitutes a tiny fraction of natural hydrogen, only 0,0153%, and can be extracted inexpensively from seawater. Tritium can be made from lithium, which is also abundant in nature.
The amount of deuterium present in one litre of water can in theory produce as much energy as the combustion of 300 litres of oil. This means that there is enough deuterium in the oceans to meet human energy needs for millions of years.
Ways to Fusion
Building a fusion power plant that can withstand the immense temperature and pressures this process produces is one of the century's greatest engineering challenges. The fuel, made up of the hydrogen isotopes deuterium and tritium, must be heated to about 100 million degrees centigrade. At that hotter-than-the-sun temperature, a fully ionized gas-plasma is formed. The plasma will then be ignited to create fusion. At present, scientists are pursuing two methods for achieving nuclear fusion: inertial and magnetic confinement.
In inertial confinement systems, ion beams or laser beams are used to compress a pea-sized deuterium-tritium fuel pellet to extremely high densities. When a critical point is reached, the pellet is ignited through shock wave heating.
Fusion power plants using this technique would ignite fuel pellets several times per second. The resulting heat is then used to generate steam that powers electricity-generating turbines.
In magnetic confinement systems, electromagnets are used to contain the plasma fuel. One of the most promising options, the tokamak device, contains the plasma in a doughnut-shaped chamber. A powerful electric current is induced in the plasma, resulting in an increase in temperature. The plasma is also heated by auxiliary systems such as microwaves, radiowaves or accelerated particles. In the process, temperatures of several hundred million degrees centigrade are achieved.
Benefits for Mankind
The potential advantages of nuclear fusion energy are manifold, as it represents a long-term, sustainable, economic and safe energy source for electricity generation.
Fuel is inexpensive and abundant in nature, while the amount of long-lived radioactive waste and greenhouse gases produced through fusion are minimal.
While research on nuclear fusion continues, many spin-offs relating to plasma physics and fusion technology are already benefiting society. These include improvements in materials research, such as ceramic, metals and coatings, and industrial processes such as welding and waste removal.
By Giovanni Verlini, IAEA Division of Public Information.
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