Scitech  Harnessing the sun to power the future

The potential, and limitations, of fusion power

Any vision of how we will meet our energy needs in the distant future is difficult to imagine without harnessing the power of nuclear fusion. Fusion represents the ability to generate essentially unlimited energy from seawater, creating virtually no waste or CO2. Physicists working on making that vision a reality have predicted that fusion power may be just thirty years away, though they have been making that prediction for a very long time.

The basic physics behind fusion are simple. Take an atom of heavy hydrogen (known as deuterium) and smash it together with another atom of heavier hydrogen (called tritium). The collision results in an atom of helium, which weighs less than either of the other two elements. We know that that a change in mass results in a massive release of energy to balance the conservation of energy. The real trick with fusion physics is providing the necessary energy to get the deuterium and tritium close enough so that they stick together, because these atoms are normally electromagnetically repelled by each other.

The sun is a perfect example of a working fusion reaction, and it has been steadily burning for the last 4.6 billion years. It gets around the issue of providing energy by virtue of the titanic force of gravity at its core – some 330,000 times the mass of the Earth all bearing down on the same spot. This causes about  4 million tonnes of mass to be converted into pure energy every second, which generates all the heat and light from the sun.

Obviously, we do not have the luxury of having 330,000 Earths worth of stuff to make our own sun, so more ingenious methods must be employed to get the required energy for fusion. The crudest working example of fusion on Earth is found in the hydrogen bomb, using the force of an atomic blast to provide the necessary energy. The resulting reaction is uncontrolled, which is fine if you are bent on causing a global apocalypse, but unfortunate if you wish to use the incredible energy created for more constructive means.

Modern research into fusion is broadly divided into two different methods for achieving the required energy: using powerful magnetic fields to heat and compress the atoms until they fuse together, or shooting a tiny amount of matter with colossal laser beams. A demonstration reactor using the first approach is currently being built in France. It is known as the International Thermonuclear Experimental Reactor (ITER) and when it is completed in 2018, its doughnut-shaped magnetic chamber will compress hydrogen gas to the millions of degrees necessary to ignite the reaction, hopefully resulting in up to five times the input energy. The research resulting from ITER will be used in the next generation fusion reactor, tentatively titled DEMO, which will be designed to be a working electrical power plant and should be online by 2040.

The laser approach is best observed at the National Ignition Facility in California. Their strategy is to use 192 of the most powerful laser beams ever created to focus the energy equivalent of 500 lightning bolts (500 terrawatts, or 500 trillion watts) on a deuterium and tritium target a couple of millimeters across for a billionth of a second. The resulting heat will cause the target to compress, resulting in fusion. It is unclear, however, how this laser approach will result in the sustained power generation necessary for a commercial power plant, since the “cool off” time required by the system is a matter of hours, if not days.

Regardless of the method we use to achieve fusion, when it is successfully achieved, it will represent a massive increase in the potential energy generation of humanity. Deuterium is easily obtained from seawater, literally allowing for the conversion of water into energy. With a supply of essentially unlimited and free energy, solutions to the problems that we will be facing will be much easier to access. And all of this may be possible in just thirty years.