Nuclear Fusion

The European Union, the USA, Russia, and Japan are just a few of the countries that take part and continue to take part in fusion research all around the world. Fusion was first linked to the development of atomic weapons when first researched by USA and USSR. This research and information was kept top secret until 1958, where it was released in Geneva. In the 1970s, there was a huge breakthrough in fusion research thanks to the Soviet tokamak and fusion research started to become big science. The JET project was then launced in the UK in 1978. This fusion project came to produce its first plasma in 1983. Success came when they tried a D-T fuel mix in 1991. A plasma temperature was produced at Princeton in the USA in 1978.

All of the stars, including the sun, are powered by fusion. Helium is formed by hydrogen atoms that fuse together with one another, and from there the matter that is formed is converted into energy. When heated to very high temperatures, hydrogen changes from the form of a gas into plasma. During this transformation, negatively charged electrons are separated from the atomic nuclei which are positively charged. It is hard for fusion to exist since positively charged nuclei deter each other. The ions move around faster as the temperature increases, and this causes the ions to collide with each other and hit each other at a much faster rate which limits the repulsion. When this occurs, nuclei fuse together and cause energy to be released.

Fusion is more likely to occur on the sun because of the mass amount of gravitational forces which help create the ideal conditions for fusion to occur. This is much harder to pull off on Earth because we do not have the same gravitational pull that the sun does. Fusion fuels, which are different isotopes of hydrogen, must be heated to enormous amounts of temperatures of up to 100 million degrees Celsius to activate the release of energy. What also must occur is that the fusion fuel must be kept comfortably dense, along with being restricted long enough (which is usually at least one second). There are now fusion research programs which are committed to accomplishing the task of “ignition” which occurs when fusion reactions occur so much that the process can be self-sustaining, the process would then be continued with the addition of fresh fuel.

There are some advantages that fusion holds that makes them different from other reactions. Fusion is an immense new source of energy. The fuels for fusion are plentiful and can be found easily. Fusion is safe because the reaction shuts down if there is any sort of malfunction or sign of danger. Also, fusion is atmospherically safe, there are no cases where it has led to any acid rain or caused the “greenhouse” effect. The radioactivity that takes place during nuclear fusion reactions can be minimized greatly with the selection of materials that are very scarce when it comes to reacting.

Two heavy forms of hydrogen produce the most feasible reaction. The two heavy forms of hydrogen are deuterium (D) and tritium (T). When D-T combine to create fusion, it releases 17.6 MeV (2.8 x 10-12 joule, compared with 200 MeV for a U-235 fission). Sea water is where deuterium naturally occurs, which makes the isotope very popular. Tritium is radioactive and does not occur in sea water, it is some what harder to find. Tritium has a half-life of about 12 years. To produce tritium, you need to make it in a conventional nuclear reactor, or in other terms, bred in a fusion system which is designed for lithium. Lithium is very abundant and can be found in quantities of up to 30 parts per million. These parts are found in the earth’s crust and in weak concentrations in the sea. The D-T reaction is the most common reaction to occur. When physicists discuss fusion reactions the D-T reaction is almost always mentioned. With much higher temperatures, there can actually be a D-D reaction which can occur.

In a fusion reactor, the goal is to absorb the neutrons into a blanket which contains lithium which surrounds the core. This then causes the lithium to be transformed into tritium and helium. The neutrons must be slowed down because they are moving so fast, in order for this to occur the blanket must be about 1 meter thick. The blanket is then heated because of this occurrence and from here; the blanket cools down again and can eventually produce steam. Conventionally this steam can be used to generate electricity. It has been difficult to design a device that can heat the D-T fuel to a high enough temperature and keep it confined long enough to release more energy through fusion.

In MFE, hundreds of cubic meters of D-T plasma at a density of less than a milligram per cubic meter are confined by a magnetic field at a few atmospheres pressure and heated to fusion temperature. Magnetic