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ITER: International Thermonuclear Experimental Reactor


ITER (“The Way” in Latin) is one of the most ambitious energy projects in the world today.

ITER, under construction.

In southern France, 35 nations* are collaborating to build the world’s largest tokamak, a magnetic fusion device that has been designed to prove the feasibility of fusion as a large-scale and carbon-free source of energy based on the same principle that powers our Sun and stars.
The experimental campaign that will be carried out at ITER is crucial to advancing fusion science and preparing the way for the fusion power plants of tomorrow.
The primary objective of ITER is the investigation and demonstration of burning plasmas—plasmas in which the energy of the helium nuclei produced by the fusion reactions is enough to maintain the temperature of the plasma, thereby reducing or eliminating the need for external heating. ITER will also test the availability and integration of technologies essential for a fusion reactor (such as superconducting magnets, remote maintenance, and systems to exhaust power from the plasma) and the validity of tritium breeding module concepts that would lead in a future reactor to tritium self-sufficiency.

Thousands of engineers and scientists have contributed to the design of ITER since the idea for an international joint experiment in fusion was first launched in 1985. The ITER Members—China, the European Union, India, Japan, Korea, Russia and the United States—are now engaged in a 35-year collaboration to build and operate the ITER experimental device, and together bring fusion to the point where a demonstration fusion reactor can be designed.

What will ITER do?

The amount of fusion energy a tokamak is capable of producing is a direct result of the number of fusion reactions taking place in its core. Scientists know that the larger the vessel, the larger the volume of the plasma … and therefore the greater the potential for fusion energy.

With ten times the plasma volume of the largest machine operating today, the ITER Tokamak will be a unique experimental tool, capable of longer plasmas and better confinement. The machine has been designed specifically to:

1) Achieve a deuterium-tritium plasma in which the fusion conditions are sustained mostly by internal fusion heating
Fusion research today is at the threshold of exploring a “burning plasma”—one in which the heat from the fusion reaction is confined within the plasma efficiently enough for the self-heating effect to dominate any other form of heating. Scientists are confident that the plasmas in ITER will not only produce much more fusion energy, but will remain stable for longer periods of time.

2) Generate 500 MW of fusion power in its plasma
The world record for fusion power is held by the European tokamak JET. In 1997, JET produced 16 MW of fusion power from a total input heating power of 24 MW (Q=0.67). ITER is designed to yield in its plasma a ten-fold return on power (Q=10), or 500 MW of fusion power from 50 MW of input heating power. ITER will not convert the heating power it produces as electricity, but—as the first of all fusion experiments in history to produce net energy gain across the plasma—it will prepare the way for the machines that can.

3) Contribute to the demonstration of the integrated operation of technologies for a fusion power plant
ITER will bridge the gap between today’s smaller-scale experimental fusion devices and the demonstration fusion power plants of the future. Scientists will be able to study plasmas under conditions similar to those expected in a future power plant and test technologies such as heating, control, diagnostics, cryogenics and remote maintenance.

4) Test tritium breeding
One of the missions for the later stages of ITER operation is to demonstrate the feasibility of producing tritium within the vacuum vessel. The world supply of tritium (used with deuterium to fuel the fusion reaction) is not sufficient to cover the needs of future power plants. ITER will provide a unique opportunity to test mockup in-vessel tritium breeding blankets in a real fusion environment.

5) Demonstrate the safety characteristics of a fusion device
ITER achieved an important landmark in fusion history when, in 2012, the ITER Organization was licensed as a nuclear operator in France based on the rigorous and impartial examination of its safety files. One of the primary goals of ITER operation is to demonstrate the control of the plasma and the fusion reactions with negligible consequences to the environment.

When will experiments begin?

ITER’s First Plasma is scheduled for December 2025*.   First Plasma will be the first time the machine is powered on, and the first act of ITER’s multi-decade operational program.   On a cleared, 42-hectare site in the south of France, building has been underway since 2010. The central Tokamak Building was handed over to the ITER Organization in March 2020 for the start of machine assembly. The first major event of this new phase was the installation of the 1,250-tonne cryostat base in May 2020. In the ITER offices around the world, the exact sequence of assembly events has been carefully orchestrated and coordinated.   The successful integration and assembly of over one million components (ten million parts), built in the ITER Members’ factories around the world and delivered to the ITER site constitutes a tremendous logistics and engineering challenge. The ITER Organization will be carrying out the work supported by a number of assembly contractors (nine contracts in all).   In November 2017, the project passed the halfway mark to First Plasma. (More here.) In July 2020, the project officially launched the machine assembly phase. (More here.) 

About ITER

ITER photo gallery

The energy source of the stars–what a marvelous ambition to harness nuclear fusion in a reactor on Earth. I encourage you to take a look through the photos of the construction of the project. The one below caught my attention:

The complexity of this construction project demands comprehensive planning and rigorous adherence to precise, pre-engineered assembly plans. The sequence of steps in assembling ITER’s million-plus components is crucial, since physical constraints on space and the interdependence of each system means that if something is left out, it may be impossible to add it in later. As complicated as this designed system is, it’s complexity pales in comparison to what we see in living organisms. Imagine building ITER with the additional engineering demand that it not only function to produce fusion energy, but that it contain the machinery to be able to reproduce itself multiple times over!


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