Fusion
Fusion is a process by which two light nuclei join together (fuse) to form a heavier nucleus, and in doing so release considerable energy. Achieving this requires high temperatures such as those that drive the fusion processes which power the sun and stars. The aim of fusion research and development is to create conditions on earth which are sufficient to generate many fusion reactions which may be harnessed to produce large amounts of thermal and/or electrical power. As there are no long-lived hazardus by-products and a plentiful supply of almost universally accessible fuel, fusion power has the potential to produce virtually limitless amounts of power in an environmentally friendly and economically viable way.
life on earth, derives its power
from fusion
Deuterium-Tritium Fusion
A particularly favourable fusion reaction for use on earth is that involving deuterium (D) and tritium (T). Deuterium is an isotope of hydrogen, so-called “heavy hydrogen”, and is found in seawater (about 33g per tonne). Tritium is an isotope of hydrogen, and is readily made from lithium, which is widely available, both from ore from the earth (4% in Australia) and also from seawater. In each D-T fusion reaction 17.6 MeV of stored energy is released, along with a Helium nucleus (He) and a neutron (n). This is about one million times the amount of energy released from a chemical reaction, e.g. the burning of fossil fuels. This is how so little fuel can produce so much energy when fusion is employed.
The deuterium-tritium fusion reaction. No radioactive ‘ash’ is produced
Plasmas and Magnetic Confinement
In order for the D-T nuclei to fuse as a result of their thermal motion, the temperature of the D-T mixture must be high. The temperature fo the solar core is about 15 million degrees C, but to release net energy on earth from D-T fusion reactions, the temperature of the D-T fuel must be higher, typically 100 million degrees C. At these temperatures matter exists in what is known as the plasma state, in which atoms are fully ionised into the electrically-charged electrons and ions. In this ionized plasma state magnetic fields may be used to confine the motion of the nuclei (magnetic confinement)..
Confining such a plasma is not trivial, at present the optimal method employs strong magnetic fields in the shape of a torus (doughnut). Experiments on present day experimental machines have already exceeded the temperatures required in a reactor, and produced short pulses of significant fusion power (up to 16 MW peak). The physics understanding of a toroidally confined plasma is not yet complete and substantial efforts are being made to do this because it will possibly lead to ways of improving the magnetic confinement scheme and making it a practical reactor (easy to operate, maintainable and cheaper). Plasma confinement studies are carried out in Australia on the National Plasma Research Facility H-1 (a type of magnetic configuration known as a heliac) at the Australian National University (ANU).
Growing World Energy Demand ? Fusion to the rescue
The world’s population is expected to exceed 20 billion by 2050. This increase will place huge demands on global energy supplies. It is widely accepted that the economically viable reserves of fossil fuels, currently our primary source of energy, are rapidly diminishing and environmental concerns of their use are increasing.
The rising population brings with it an increased demand for energy. In addition, the growth of energy demand. These facts combine to lead to a prediction of doubling of the world’s energy demand from 2000 to 2050.
Fusion offers a sustainable, safe, environmentally-friendly, and economically competitive energy source. With fusion fuel in great abundance it appears to be the only truly long-term, environmentally-friendly solution to meet the world’s bulk energy demands.
A typical modern electric power plant will produce ~1000MW. The table below shows the fuel consumption over one year at this rate. The high energy density of the fusion fuel and its abundance are compelling arguments to realise this source of energy.
|
METHOD |
FUEL |
|
Coal |
2,700,000 tonnes |
|
Oil |
1,900,000 tonnes |
|
Fission |
28 tonnes of Uranium Oxide |
|
Fusion |
100kg D & 150kg T |
Fusion is a source of large amounts of high temperature, thermal power which can be used directly in industrial processes (e.g. hydrogen production and desalination) or in the generation of electrical power. This makes it a versatile source of energy. The other sources of sustainable energy, the so-called “renewables” e.g. hydro-electric, wind, wave, geothermal, and solar power are not yet able to provide base-load electrical power on a sufficient scale, but certainly play their roles in appropriate situations.