Powering A Star Machine


Progress on the development of ITER, the world’s widest collaborative nuclear fusion reactor and research centre, recently entered a new phase with the commencement of work on creating the infrastructure that will provide the vast amounts of electrical power needed to fuel the device.

The International Thermonuclear Experimental Reactor, or ITER, is a project involving countries representing over half of the world’s population working together to find a viable and efficient alternative energy source to fossil fuels; China, India, Russia, Japan, South Korea, the US and the EU are all contributors. The site itself is situated in the South of France, where preparations began in 2007 with the clearing and leveling of 42 hectares of land. The building of the on-site headquarters was completed in 2012. January this year saw the first component of the tokamak fusion device arrive on site, and in April works began on the development of the electrical infrastructure.

A tokamak is the name for a toroidal (doughnut-shaped) device that uses magnetic fields to confine a plasma (an ionized gas, meaning the electrons have been stripped from their nuclei), and is the favoured design for fusion reactors. In nuclear fusion, nuclei are forced together under extremely high pressures and temperatures to create new, bigger nuclei, releasing vast amounts of energy in the process. This is a constantly ongoing process in stars, where the temperatures and pressures are created by the star’s own gravity. Hydrogen fuses to form helium, and in very massive stars, even heavier elements, including carbon, nitrogen and oxygen, all the way up to iron in the cores of the most massive stars. Elements heavier than iron can only be created in the most energetic explosions in the universe, supernovae. On Earth, most experiments so far have only successfully been able to fuse up to helium, and at an efficiency of close to 0, meaning it takes as much energy to heat the plasma as is given out in fusion energy. There are different candidates for possible reactor fuels, the generally favoured combination, and the one that will be used by ITER being a deuterium-tritium reaction. Deuterium and tritium are both isotopes of hydrogen, respectively consisting of one proton and one neutron, and one proton and two neutrons. Deuterium and tritium fuse to form helium, with two protons and two neutrons, leaving one neutron spare. The energy production comes from the fact that a helium nucleus and one neutron actually have a mass very slightly lower than that of a deuterium nucleus and a tritium nucleus. Thanks to Einstein’s most famous equation, we know that this apparent destruction of mass does not in fact defy the laws of nature, but is converted to kinetic energy with a conversion factor of the speed of light squared, 9×10¹⁶. It is the spare neutron that carries away most of this energy, which is then absorbed by a surrounding blanket of lithium which slows the neutron through collisions, converting its energy to heat to then power a generator.

The trick is in managing to create a plasma that can be sustained for significant periods of time. At the moment, it takes as much power to create the fusion reaction as is given back out in energy. In most cases, a plasma only lasts for fractions of a second before collapse. If it were able to be held for longer periods of time, it would be self-sustaining and only need the initial burst of energy to heat it in order to create vast amounts of energy.  This is why ITER is such an important project for the entire scientific community. Completion of the assembly of the tokamak is projected to occur in 2019, with hopes for creating the first plasma in ITER in 2020 and the beginning of deuterium-tritium operations in 2027.

Feature image by Bethany Westall. 


Physics student and regular freelance science communicator, shooting for the stars. I'm your Science Editor and with the help of a team of talented writers, strive to bring you the most interesting and relevant science stories.

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