ITER Collaboration

ITER Participants

Fig. 1: ITER participants. (Source: Wikipedia Commons)

The ITER collaboration is an international nuclear fusion project designed to prove feasibility of fusion as a large-scale source of energy. It involves 35 nations (see Fig. 1) collaborating towards building the world's largest tokamak. The idea of an international joint experiment in fusion was first proposed in 1985. Now, 37 years after that initial step, the ITER Members include China, the European Union, India, Japan, Korea, Russia and the United States.

ITER's Design

The project consists of building a tokamak. A tokamak is a device designed to confine plasma in the shape of a torus using a powerful magnetic field. It was invented in 1968 in the USSR and since then it has been replicated in other countries, for example the DIII-D tokamak in San Diego, CA and JET in the UK. Fig. 2 shows a schematic of ITER tokamak. It must be said that there are other toroidal machines like Z-pinch and Stellarators with their own pros and cons. The choice of the tokamak design is chiefly that tokamaks suppress instabilities that stellarators and Z-pinch devices cannot. There is also more data about the behavior of plasma inside tokamaks, and scaling is easier in terms of design and construction versus stellarators with very complicated geometries.

Fig. 2: ITER tokamak and Plant Systems. (Courtesy of Oak Ridge National Laboratory. Source: Wikimedia Commons)

The success of the European tokamak JET is also a factor to consider. JET holds the world record for fusion power. It produced 16 MW from a total input heating power of 24 MW (Q=0.67) in 1997. [1,2] ITER has been designed to produce burning plasma with a ten-fold return on energy (Q=10). This translates to achieving 500 MW of fusion power from 50 MW of input heating power and a steady-state plasma with at least Q=5. [2,3] It should be noted that ITER's goal is not to capture this energy and produce electricity from it but to produce net energy gain. How to build a power plant based on fusion is still an unresolved engineering problem. If successful, this will allow scientists to study and test plasma, heating systems, control, diagnostics, cryogenics, among others, under steady-state conditions of Q > 1.

ITER's Goals

Fig. 3: The deuterium-tritium fusion reaction. (Source: Wikipedia Commons)

One key scientific goal of ITER is achieving a deuterium-tritium plasma and being able to sustain it through internal heating. [4] Internal heating means to have a burning plasma i.e., a plasma efficiently confined such that the fusion reactions themselves are the primary source of heating in the plasma. This is necessary to sustain and propagate the burn, which enables high energy gain. [5] Now, achieving a burning plasma for a long duration is challenging. For example, burning plasmas can be achieved in nuclear weapons during explosion, so the challenge here is to have a controlled self-sustained burning plasma. By increasing the size of the tokamak, one increases the chances for nuclear fusion reactions to occur which justifies the size of ITER. It remains to be proven that burn with the necessary energy gain canbe achieved.

Having a deuterium-tritium plasma refers to the hydrogen isotopes used to generate the fusion reaction. Fig. 3 shows a cartoon of a deuterium-tritium fusion reaction. Twentieth-century fusion science identified this reaction as the most efficient in the laboratory setting, meaning that this fusion reaction produces the highest energy gain at the lowest temperature. [1,2] Deuterium is widely available, harmless and can be distilled from ordinary water. On the other hand, Tritium is a radioactive element with a half-life of 12.3 years. [6] Tritium is not abundant but can be produced (bred) when neutrons escaping the plasma interact with the lithium contained in the blanket wall of the tokamak. [7]

The ITER project has scheduled the first plasma for December 2025 and plans to start the Deuterium-Tritium operation in 2036.

© Claudia Parisuana-Barranca. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] J. Mlynár, "Focus on JET," European Centre of Fusion Research, EFD-R(07)91, March 2007.

[2] J. Kates-Harbeck, "The ITER Project, Physics 241, Stanford University, Winter 2011.

[3] "Summary of the ITER Final Design Report," International Atomic Energy Agency, IAEA/ITER EDA/DS/22, July 2001.

[4] "ITER Final Design Report, Cost Review and Safety Analysis (FDR) and Relevant Documents," International Atomic Energy Agency, IAEA-ITER EDA/DS/14, page 8, March 1999

[5] A. B. Zylstra et al., "Burning Plasma Achieved in Inertial Fusion," Nature 601, 542 (2022).

[6] B. D. Lemeshko et al., "Lifetime and Shelf Life of Sealed Tritium-Filled Plasma Focus Chambers with Gas Generator," Matter Radiat. Extrem. 2, 303 (2017).

[7] M. Rubel, "Tritium Breeding and Impact on Wall Materials and Components of Diagnostic Systems," J. Fusion Energy 38, 315 (2019).