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STAR POWER

Star Power

For more than 60 years, scientists have been looking for a way to safely produce a commercial energy source using thermonuclear fusion. Since fusion requires temperatures and pressures similar to those found in the core of the sun, developing such technology has obviously been extraordinarily difficult. But an international effort undertaken by seven countries, known as ITER, looks poised to make fusion power a reality.

The Quest for Fusion Power
All stars, including our sun, generate energy through fusion reactions deep in their cores. Because the extremely high temperatures needed for such reactions would instantly vaporize any solid materials from which a reactor might be constructed, a large part of the challenge has been creating a system that can effectively contain these reactions. While nothing on Earth could possibly withstand these intense conditions, in 1968 Russian scientists discovered that “nothing” is exactly what was needed, when they successfully developed a special vacuum vessel known as a tokamak to house the reaction. Another crucial milestone was reached in 1991, when the Joint European Torus (JET) used the tokamak design to achieve the first controlled release of fusion power. Today the race is on to replicate such a reaction on a much larger scale, and ITER, which is Latin for “the way,” aims to achieve this goal.

As JET’s successor, ITER is an international research and engineering project funded by the United States, the European Union (EU), India, Japan, China, Russia, and South Korea. The project is based in Cadarache, France, where the ITER team is currently constructing an experimental tokomak reactor twice the size of any previous design. Over the next several years, the ITER team will test the viability of the reactor to produce sufficient fusion for generating a commercial source of electricity. According to the project’s timeline, the reactor should be operational by 2020, which would set the stage for the large-scale production of electrical power from fusion as early as 2040.

If successful, ITER’s work could usher us into a new era when the world will obtain much of its energy needs from an inexhaustible, environmentally safe, and universally available resource.

Why Fusion
With the growing scarcity of fossil fuels and the mounting effects of climate change, there is an urgent demand for new, sustainable sources of energy. Fusion power has the potential to not only meet global energy needs, but also to provide a renewable energy source that’s far more ecofriendly than both carbon-based energy production and conventional nuclear reactors.

Unlike fission reactions in traditional nuclear power plants, where a single atom is split into two smaller ones, fusion involves fusing two or more small atoms into a larger one. In the case of ITER, the reactor will fuse deuterium and tritium, as the pairing of these two hydrogen isotopes produces the highest energy gain at the lowest temperatures. These fuel sources are also quite sustainable: Deuterium is widely available in nature, and can be distilled from seawater, making it nearly inexhaustible. And while tritium occurs in trace quantities in nature, the isotope could be produced by the fusion reaction itself in a process known as “tritium breeding.” Initially, ITER will draw upon a limited supply of tritium to achieve fusion, but once the reactor becomes operational, the new tritium that’s bred by fusion can be sustained indefinitely.

As for environmental impact, fusion produces virtually no carbon dioxide or other atmospheric pollutants. Its major byproduct is helium, which is inert and non-toxic. Fusion’s other waste products have very short half-lives compared to those from conventional nuclear reactors. Moreover, compared to other sustainable power sources like wind, solar and hydroelectric, which all have a relatively low power output, a successful fusion reactor would produce an energy density that exceeds even large fission power plants.

ITER

The Process Despite its efficiency, fusing deuterium and tritium still requires temperatures of 150 million-degrees Celsius—10-times hotter than the sun’s core. At such high temperatures, the electrostatic repulsion that exists between the positively charged nuclei of the deuterium and tritium will be overcome, whereby the two atoms will smash into one another and fuse. This process turns the fuel into plasma—a hot, electrically charged gas—and ultimately produces helium atoms as well as highenergy neutrons.

7 ITER1Large

A cut-away of the ITER Tokamak. Note the vacuum chamber at the machine’s midsection in yellow. With a height of 29 metres and a diameter of 28 metres, ITER will be the world's largest tokamak. ©ITER Organization

While fusion is a simple concept, it’s extremely difficult to achieve—at least here on Earth. For one, these tremendous temperatures make using any type of solid material to contain the plasma impossible. However, the tokamak vacuum vessel has proven to be a reliable container for such hellish conditions. The vacuum not only provides a sterile environment for plasma to populate, but it also keeps the hot plasma away from the reactor’s inner walls. Unfortunately, the high temperatures aren’t the only challenge. Left alone, the plasma would expand and eventually come in contact with the walls, which would instantly stop the reaction, so the tokamak also employs powerful magnetic fields to trap the plasma. Because plasma consists of charged particles, it can be shaped by magnetic forces. By surrounding the tokamak with huge magnets, the charged particles in the plasma will follow the magnetic field lines, just like iron filings placed next to a magnet. This allows the plasma to be held in place and shaped into a doughnutlike form, called a torus. Isolated by the magnetic field, the plasma is trapped in this spiraling torus, where it’s heated using a combination of three methods: high-intensity electrical current (ohmic heating), particle accelerators that shoot high-energy particles into the plasma (neutral beam injection), and “microwaving” the plasma with highfrequency electromagnetic waves.

Fusion power has the potential to not only meet global energy needs, but also to provide a renewable energy source that’s far more eco-friendly than both carbon-based energy production and conventional nuclear reactors.

7 ITER4To capture the fusion energy and eventually use it to produce electricity, the tokamak’s outer walls will be lined with special “blanket modules” made from 440 steel blocks nearly a half-meter thick. The inside surface of the walls directly facing the plasma will be lined with tiles made of beryllium, which can withstand much higher temperatures than steel. The outer blanket wall is designed to capture the neutrons produced by the reaction and turn them into energy.

Since the helium produced by fusion carries an electric charge, it will respond to the magnetic fields and be locked in the plasma. However, the neutrons have no electric charge, so they will not be affected by the magnets and will escape the plasma and get absorbed by the blanket. The heat energy generated by the neutrons will then be extracted from the blanket through a cooling system, which will eventually be used to power a steam turbine to produce electricity in future power plants. Furthermore, some of the blanket modules will contain lithium, which will react with the neutrons to produce both tritium and helium. The Vacuum Pumps and Systems tritium that’s bred by the blanket can then be removed and recycled to use as fuel for future reactions, thereby making the process self-sustaining. Overall, the ITER reactor is designed to produce 500 megawatts of power from 50 megawatts of input energy.

Energy of the Future
As an experimental project, ITER is merely designed to prove the scientific and technological feasibility of a fusion reactor. Once this has been achieved, a successor device to ITER, known as the demonstration fusion reactor (DEMO), will take the final step in the long journey toward commercial fusion power. DEMO will use the technologies tested by ITER to develop the first fully functioning fusion power plant. From there, it is quite possible that similar reactors will be constructed around the world to provide a significant portion of the world’s future energy needs. As the Latin name for the project implies, this would mean that ITER is truly “the way” to new energy.

Cut-away of the ITER Vacuum Vessel showing part of the Blanket modules attached to the inner wall. ©ITER Organization

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