Solar fusion is fairly complex. It starts with hydrogen and requires three different steps to create a helium atom. It also requires higher temperature and pressure than is currently viable in man-made fusion reactors. The deuterium-tritium reaction is the best way to create fusion under laboratory conditions. This reaction is over one million times easier to initiate than the hydrogen-hydrogen reaction that takes place in the sun’s core.
A hydrogen atom consists of a proton and an electron. Deuterium is a hydrogen isotope with an extra neutron, and can be extracted from water. Tritium has two neutrons and is a by-product of nuclear reactions. It can be extracted from fission power plants.
When deuterium and tritium meet at an extremely high temperature and under the right conditions, they fuse to form helium, with one neutron left over. Smaller nuclear forces in deuterium and tritium mean the reaction can take place at much lower temperatures than the hydrogen.
Nuclear force is the strong energy that binds nuclei together.
The reactor design currently favoured is based on the tokamok, a design originally from the former Soviet Union. It is a donut-shaped reactor which has a magnetic field circling the reactor core. The core consists of a leak-tight vacuum chamber with a heat-resistant wall.
For fusion to occur, fuel must be heated to temperatures high enough that the gas becomes fully ionized. At temperatures over 100,000 °C, atoms separate into nuclei and free electrons. This state of matter is called plasma. The plasma can’t remain in this state for long, even at temperatures in excess of 100 million °C. To counter this problem, the reactor is enclosed in a magnetic field, which makes the particles move in tight spirals around the field lines. This field maintains control over the plasma material.
The magnetic force induces an electric field that heats the fuel to the plasma state. Radio waves or high velocity neutral atoms can provide additional heating, which is required in the current reactors. Within this setting, fusion can occur.
As long as small amounts of fuel are injected into the core and the plasma volume remains high enough, the reaction will continue. Thus, it is easy to stop the reaction by cutting off the fuel supply, if needed.
Energy is then carried away outside by a neutron stream outside the ring, and converted into electricity.
Today’s reactor designs have a net loss of energy—more energy is needed to start the reaction than the reaction can provide. With more research and improving designs, such as ITER, however, fusion power is on the verge of becoming a practical reality.
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