Yesterday, dignitaries attended a components handover ceremony at the construction site of the International Thermonuclear Experimental Reactor in southern France. The ITER project is an experiment aimed at reaching the next stage in the evolution of nuclear energy as a means of generating emissions-free electricity.
The section recently installed—the cryostat base and lower cylinder—paves the way for the installation of the tokamak, the technology design chosen to house the powerful magnetic field that will encase the ultra-hot plasma fusion core.
“Manufactured by India, the ITER cryostat is 16,000 cubic meters,” ITER officials said in a release. “Its diameter and height are both almost 30 meters and it weighs 3,850 tons. Because of its bulk, it is being fabricated in four main sections: the base, lower cylinder, upper cylinder, and top lid.”
The entire project is now 65% complete, the officials said. The world’s first commercial-scale fusion reactor project is on track to officially launch operations at the end of 2025, said spokeswoman Sabina Griffith, but it will take at least a decade to fully power up the facility.
“The date for First Plasma is set; we will push the button in December 2025,” Griffith said. “It will take another 10 years until we reach full deuterium-tritium operations.” Thirty-five nations are cooperating on the project to bring fusion power to the masses.
Achieving controlled fusion reactions that net more power than they take to generate, and at commercial scale, is seen as a potential answer to climate change. Fusion energy would eliminate the need for fossil fuels and solve the intermittency and reliability concerns inherent with renewable energy sources. The energy would be generated without the dangerous amounts of radiation that raises concerns about fission nuclear energy.
Officials say the ITER nuclear fusion reactor is poised to be the most complicated piece of machinery ever built. It will contain the world’s largest superconducting magnets, needed to generate a magnetic field powerful enough to contain a plasma that will reach temperatures of 150 million degrees Celsius, about 10 times hotter than the center of the sun.
Griffith said more milestones will be cleared as soon as construction continues. “We will see the arrival of the first major Tokamak components like the first PF Coil from China (a European contribution), a Vacuum Vessel sector from Korea and first TF coils (from Europe and Japan) this autumn,” Griffith said in an email. “This will lead us to the official start of assembly in spring next year.”
Fusion is the energy source of the Universe, occuring in the core of the Sun and stars. Without fusion, there would be no life on Earth.
What we see as light and feel as warmth is the result of a fusion reaction in the core of our Sun: hydrogen nuclei collide, fuse into heavier helium atoms and release tremendous amounts of energy in the process.
Over billions of years, the gravitational forces at play in the Universe have caused the hydrogen clouds of the early Universe to gather into massive stellar bodies. In the extreme density and temperature of the stars, including our Sun, fusion occurs.
HOW DOES FUSION PRODUCE ENERGY?
The most efficient fusion reaction in the laboratory setting is the reaction between two hydrogen isotopes deuterium (D) and tritium (T). The fusion of these light hydrogen atoms produces a heavier element, helium, and one neutron.
Atoms never rest: the hotter they are, the faster they move. In the Sun's core, where temperatures reach 15,000,000 °C, hydrogen atoms are in a constant state of agitation. As they collide at very high speeds, the natural electrostatic repulsion that exists between the positive charges of their nuclei is overcome and the atoms fuse. The fusion of light hydrogen atoms produces a heavier element, helium.
Every second, our Sun turns 600 million tonnes of hydrogen into helium, releasing an enormous amount of energy. But without the benefit of gravitational forces at work in our Universe, achieving fusion on Earth has required a different approach.
Twentieth-century fusion science identified the most efficient fusion reaction in the laboratory setting to be the reaction between two hydrogen (H) isotopes deuterium (D) and tritium (T). The DT fusion reaction produces the highest energy gain at the "lowest" temperatures. It requires nonetheless temperatures of 150,000,000 degrees Celsius—ten times higher than the hydrogen reaction occurring in the Sun.
Power plants everywhere generate electricity by converting mechanical power such as the rotation of a turbine into electrical power. In a coal-fired steam station, the combustion of coal turns water into steam and the steam in turn drives turbine generators to produce electricity. Power plants today rely either on fossil fuels, nuclear fission, or renewable sources like hydro.
The tokamak is an experimental machine designed to harness the energy of fusion. Inside a tokamak, the energy produced through the fusion of atoms is absorbed as heat in the walls of the vessel. Just like a conventional power plant, a fusion power plant will use this heat to produce steam and then electricity by way of turbines and generators.
We're not there yet, however. The operation of ITER will allow the ITER Members to test long-pulse operation and the many required technologies at reactor scale, but the machine won't be equipped to produce electricity. More here.
HOW DOES IT WORK?
The heart of a tokamak is its doughnut-shaped vacuum chamber. Inside, under the influence of extreme heat and pressure, gaseous hydrogen fuel becomes a plasma—a hot, electrically charged gas. In a star as in a fusion device, plasmas provide the environment in which light elements can fuse and yield energy.
The charged particles of the plasma can be shaped and controlled by the massive magnetic coils placed around the vessel; physicists use this important property to confine the hot plasma away from the vessel walls. The term "tokamak" comes to us from a Russian acronym that stands for "toroidal chamber with magnetic coils" (тороидальная камера с магнитными катушками).
To start the process, air and impurities are first evacuated from the vacuum chamber. Next, the magnet systems that will help to confine and control the plasma are charged up and the gaseous fuel is introduced. As a powerful electrical current is run through the vessel, the gas breaks down electrically, becomes ionized (electrons are stripped from the nuclei) and forms a plasma.
As the plasma particles become energized and collide they also begin to heat up. Auxiliary heating methods help to bring the plasma to fusion temperatures (between 150 and 300 million °C). Particles "energized" to such a degree can overcome their natural electromagnetic repulsion on collision to fuse, releasing huge amounts of energy.
First developed by Soviet research in the late 1960s, the tokamak has been adopted around the world as the most promising configuration of magnetic fusion device. ITER will be the world's largest tokamak—twice the size of the largest machine currently in operation, with ten times the plasma chamber volume.
In 1955 a young engineer working on nuclear fusion decided to work out exactly how enormous the task of achieving fusion is. Although his colleagues were optimistic about their prospects, he wanted to prove it to himself. His name was John Lawson, and his findings—that the conditions for fusion power relied on three vital quantities—became the landmark Lawson Criteria.
The genesis of Lawson's Criteria is simple enough—he calculated the requirements for more energy to be created than is put in, and came up with a dependence on three quantities: temperature (T), density (n) and confinement time (τ)*. With only small evolution thanks to some subtle changes of definition, this is basically the same figure of merit used by today's fusion scientists, the triple product, nτT.
The amount of energy created relies on particles colliding and fusing—the number of collisions is related to the number of particles in a certain region—thus n, the number density (not mass density) is Lawson's first criterion. This would seem encouraging for the prospective experiment, as creating high pressure is relatively easy. However there is a catch.
At higher densities a process known as bremsstrahlung rears its ugly head, in which collisions between nuclei and electrons generate radiation. Bremsstrahlung can become so dominant that all the power in the plasma is radiated away; the optimum density conditions are surprisingly low, around a million times less dense than air.
Nonetheless the fusion collisions—between the nuclei—have to be at high speed. This allows the nuclei to overcome their electrostatic repulsion, and get close enough for the strong force that governs fusion to take over and stick the particles together. The speed of a gas or plasma particle is equivalent to its temperature: the second of Lawson's criteria.
Again there is a limit—if the two particles are moving really fast then the time they are in close enough proximity for fusion to occur decreases. The bremsstrahlung also increases at higher temperatures, due to faster moving electrons. The Goldilocks temperature turns out to be in the vicinity of 100—200 million degrees, a seemingly huge task in the fifties that has become a standard condition today.
