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Nuclear Fusion- Energy from the Stars

11/16/2010

Every day, space shows us that nuclear fusion can produce considerable amounts of energy. The only problem is that this phenomenon takes place a long way from Earth, in conditions that are not found on our planet. Science is endeavoring to reproduce the conditions required for fusion.

A Natural Phenomenon inside the Sun...

Nuclear fusion^1-2 consists of combining two light atomic nuclei to form a heavier nucleus. This releases a huge amount of energy. The Sun converts 600 million tons of hydrogen into helium every second³, releasing considerable amounts of energy.

The Sun converts 600 million tons of hydrogen into helium every second.

During fusion, hydrogen forms a plasma (the state of matter when heated to a very high temperature). The atomic nuclei in the plasma shed their electrons and the forces of repulsion between these are very high. However, some fuse and change into helium, releasing large amounts of energy. On the Sun, the probability that two hydrogen nuclei will fuse is extremely low but this is offset by the huge numbers of nuclei present.

...Difficult to Reproduce on Earth

Nuclear fusion can be reproduced on Earth as long as an extremely high temperature can be reached - up to 200 million degrees⁴. The problem is that no material can withstand this temperature.

To reproduce nuclear fusion on Earth⁵, researchers are mainly working on magnetic confinement, which involves controlling a plasma confined in an annular vacuum by means of highly intense magnetic fields at a very high temperature.

Nuclear fusion can be reproduced on earth as long as an extremely high temperature can be reached - up to 200 million degrees.

To increase the probability of fusion, hydrogen isotopes are used - these are atoms with the same number of protons but a different number of neutrons. They are deuterium (²H) and tritium (³H).

• Deuterium is extracted from seawater.

• Tritium is not found on Earth or in the lower layers of the atmosphere. It is produced in minute quantities by fission inside conventional nuclear reactors. It can also be generated by irradiating lithium, an element that is found in abundance on Earth. Finally, contrary to deuterium, tritium has a short half-life (the time it takes radioactivity to decrease by half) of just 12 years⁶.

Nuclear fusion was discovered by a woman.

True. A few decades after the work of Nobel Prize winner Marie Curie on radioactivity, another woman played an active role in the discovery of nuclear fusion. Austrian physicist Lise Meitner worked alongside German chemists Otto Hahn and Fritz Strassmann on studies culminating in its description in 1938.

At the Core of Magnetic Confinement

The process of producing energy from nuclear fusion is as follows:

• Plasma is placed inside a vacuum vessel (a hermetically sealed stainless steel container forming an initial safety barrier), then ionized (the number of its atoms is changed), and heated by a very intense electrical discharge.

• High-energy deuterium is added regularly and the emission of radio waves towards the plasma and production of high-energy helium nuclei help maintain the extremely high temperature required for a fusion reaction.

• Electric currents circulating in the plasma and in coils outside the vacuum vessel create the intense magnetic field required for plasma confinement (50,000 times the earth's magnetic field).

• Fusion releases neutrons released to provide energy that is then captured. These neutrons are not sensitive to the magnetic field because their electrical charge is neutral, so they escape outside the confinement vessel and bounce off the walls of the reactor, heating the vessel until it is white-hot.

• A heat-transfer fluid recovers this heat on the outside, which transmits it to a secondary circuit. As in nuclear fission power plants, this circuit generates water vapor used to produce electricity.