Stellarator vs. Tokamak

Two types of experimental nuclear fusion reactor. Both use magnets to try to keep hydrogen isotopes deuterium and tritium under enough temperature and pressure to fuse their nuclei into helium, but, said the Frankfurter Allgemeine, the tokamak system can only work in pulsed operation while the less common stellarator can do continuous operation, making it useful for research into electricity-generating applications.

Physicists say the bigger a pulsing tokamak is, the better it works. The world’s largest tokamak experimental fusion reactor is under construction in southern France. The “Iter” reactor in Cadarache is a joint project of Europe, Japan, Russia, China, South Korea, India and the U.S., originally budgeted at 4.6 billion euros with completion in 2020 but now expected to cost ~15 billion and be at least two years late. A project manager said the extra costs are because the original estimates were only for construction costs and did not include e.g. insurance, manufacturers’ profit and administration costs. Because each of the seven partners wants to acquire all knowledge related to this reactor so they can build copies at home, many of the parts have been manufactured in factories in multiple countries instead of by one contractor, with the added risks this entails.

The world’s largest stellarator experimental fusion reactor officially completed construction this month in Greifswald, Germany. The Max Planck Institute said since 1995 construction of the “Wendelstein 7-X” has been financed by approx. 201 million euros from the E.U.’s Euratom program, 672 million from Germany and 131 million from the state of Mecklenburg-Vorpommern; it was originally budgeted at 500 million euros but ended up costing >1 billion.

The stellarator in Greifswald is not intended to fuse hydrogen atoms but is intended to research electricity generation via fusion. The tokamak in Cadarache intends to use 50 megawatts to produce 500 megawatts via fusion, getting more energy out than was put in for the first time said a representative; researchers there are interested in pure physics research but also developing technologies that will be used in the next generation of fusion reactors, probably not available before 2050.

The world’s previous largest tokamak experimental fusion reactor was at Culham, U.K., and only managed to produce 60% of the energy that it fed into the reaction.

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