What is the meaning of Fusion ?

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Nuclear fusion is the process by which two light atomic nuclei combine to form one heavier atomic nucleus. ... Unlike fission reactions, fusion based energy technology would not produce long-lived radioactive waste.

With its high energy yields, low nuclear waste production, and lack of air pollution, fusion, the same source that powers stars, could provide an alternative to conventional energy sources. But what drives this process?

Fusion occurs when two light atoms bond together, or fuse, to make a heavier one. The total mass of the new atom is less than that of the two that formed it; the "missing" mass is given off as energy, as described by Albert Einstein's famous "E=mc2" equation.

Fusion is the dominant source of energy for stars in the universe. It is also a potential energy source on Earth. When set off in an intentionally uncontrolled chain reaction, it drives the hydrogen bomb. Fusion is also being considered as a possibility to power crafts through space.

Fusion differs from fission, which splits atoms and results in substantial radioactive waste, which is hazardous.

There are several "recipes" for cooking up fusion, which rely on different atomic combinations.

Deuterium-deuterium fusion: Theoretically more promising than deuterium-tritium because of the ease of obtaining the two deuterium atoms, this method is also more challenging because it requires temperatures too high to be feasible at present. However, the process yields more energy than deuterium-tritium fusion.

Proton-proton fusion: The dominant driver for stars like the sun with core temperatures under 27 million degrees F (15 million degrees C), proton-proton fusion begins with two protons and ultimately yields high energy particles such as positrons, neutrinos, and gamma rays.

Nuclear fusion is the process by which two light atomic nuclei combine to form one heavier atomic nucleus. As an example, a proton (the nucleus of a hydrogen atom) and a neutron will, under the proper circumstances, combine to form a deuteron (the nucleus of an atom of "heavy" hydrogen).

In general, the mass of the heavier product nucleus is less than the total mass of the two lighter nuclei. Nuclear fusion is the initial driving process of nucelosynthesis.

The practical problems of building a fusion power plant are formidable, and the technology to construct a suitable containment vessel or field in which controlled fusion reactions could take place does not yet exist. Currently the only fusion reactions that take place on Earth are uncontrolled fusion reaction in nuclear weapons (e.g., H-bombs).

In April, 2003, Sandia scientists reported that they had achieved controlled thermonuclear fusion in a pulsed power source. If ultimately reproduced and verified, the process, and other competing approaches to controlled fusion, holds the promise of nearly unlimited clean power generation. Unlike fission reactions, fusion based energy technology would not produce long-lived radioactive waste.

Instead of using magnetic containment to compress hydrogen and thereby achieve temperatures hot enough for fusion to occur, Sandia scientists used pulsed releases of current to achieve a rapid series of limited micro fusion reactions. Using an improved and more powerful Z accelerator, high current is induced in a tungsten wire cage surrounding a 2 mm plastic capsule containing deuterium (an heavier isotope of hydrogen).

The tungsten cage is vaporized, but the short-lived current impulse generated in the wires creates a powerful magnetic pulse and shock-wave of superheated tungsten that creates an intense x-ray source that, along with the shockwave compresses and heats the hydrogen to more than 20 million degrees Fahrenheit (more than 11 million degrees Celsius) to induce fusion.

The Sandia reaction process contrasts with another promising approach undertaken at the Lawrence Livermore National Laboratory (LLNL) that seeks to initiate fusion reactions by shining high energy lasers on hydrogen globules. The LLNL approach will be further explored at the National Ignition Facility.

Scientists who worked on the first fission (atomic) bomb during World War II were aware of the potential for building an even more powerful bomb that operated on fusion principles.

A fusion bomb uses a fission bomb as a trigger (a source of heat and pressure to create a fusion chain reaction. In the microseconds following a fission explosion fusion begins to occur within the casing surrounding the fission bomb.

Protons, deuterons, and tritons begin fusing with each other, releasing more energy, and initiating other fusion reactions among other hydrogen isotopes.

The fusion sequence. When a proton and neutron combine, the mass of the resulting deuteron is 0.00239 atomic mass units (amu) less than the total mass of the proton and neutron combined. This "loss" of mass is expressed in the form of 2.23 MeV (million electron volts) of kinetic energy of the deuteron and other particles and as other forms of energy produced during the reaction.

Nuclear fusion reactions are like nuclear fission reactions, therefore, in that some quantity of mass is transformed into energy. This is the reason stars "shine" .

The particles most commonly involved in nuclear fusion reactions include the proton, neutron, deuteron, a triton (a proton combined with two neutrons), a helium-3 nucleus (two protons combined with a neutron), and a helium-4 nucleus (two protons combined with two neutrons).

Except for the neutron, all of these particles carry at least one positive electrical charge. That means that fusion reactions always require very large amounts of energy in order to overcome the force of repulsion between two like-charged particles. For example, in order to fuse two protons, enough energy must be provided to overcome the force of repulsion between the two positively charged particles.

As early as the 1930s, a number of physicists considered the possibility that nuclear fusion reactions might be the mechanism by which energy is generated in the stars. No familiar type of chemical reaction, such as combustion or oxidation, could possibly explain the vast amounts of energy released by even the smallest star.

In 1939, the German-American physicist Hans Bethe worked out the mathematics of energy generation in which a proton first fuses with a carbon atom to form a nitrogen atom. The reaction then continues through a series of five more steps, the net result of which is that four protons are consumed in the generation of one helium atom.