When creating the sun on earth is just a metaphor


Richard Pitt, leading plasma scientist at ITER project. With his fusion goggles. Like Dr Octopus.

Some reflexions about a recent study trip Cadarache (south of France), on the ITER building site. Where the largest international scientific and industrial consortium (European countries, including Switzerland, USA, Russia, Chine, South Korea, Japan and India) is patiently constructing what will be the first tokamak-genre nuclear fusion reactor. It should give up ten times more energy than what will be needed to trigger the burning reaction: from 50 to 500 MW. In 2022, according to the latest schedules.

During one and a half day, thanks to EUSJA, the directors of the ITER project (meaning the way in latin) and some of its chief scientists, plus its media service, have assaulted us with a torrent of datas and infos. According to which, ITER is bloody complicated. A reasonable explanation of its immense costs – around 15 bilion euros. The complex logistics of buildings parts of the reactor in different countries and assembling them afterwards onsite with strict tolerances – of the mm order – in particular was emphasized many times to us. For those who read french, i include a copy of the article I published for my swiss newspaper (24 heures, based in Lausanne).

But one point I’d like to come to is the use of metaphors for describing complex science to a wide audience. Metaphors given by the scientists themselves and which we tend to reproduce. Fusion between atoms is invariably connected with what happens in the stars, eg our sun. And thus, a fusion reactor must reproduce that, ending to be a sun on earth. Which is nice when you have to find a short and striking title for your article.

But as physicist Richard Pitt, from ITER, explained to us, fusion on earth doesn’t work like that. In the sun, and in the stars in general, fusion happens between hydrogen atoms, because of the work of gravity. And because, the ambient being a plasma, there is such an awful lot of neutrons around. “I you want to do that on Earth, first of all, you don’t have a mass the equivalent of the sun, which is fortunate, says same Richard Pitt. And second, without that mass, it would take ages. Many of them.” No sun on earth, then, no sir. We have many other examples of these approximative metaphors, in medicine or robotics.

He’s right, of course. So we have to use two isotopes og Hydrogen, Deuterium and Tritium. With temperature (or velocity, which is the same) much higher than in the sun’s heart. Mind you, as the plasmas used in a tokamak are very undense, would you consider to put one of your arms into it – according to Richard Pitt, who has a british sense of humour – it would only vaporize that arm. Not your entire body nor the whole french Provence region.

But then, why such stringent security measures on the ITER site? with armed guards, and so on? Very easy. Tritium, a fairly radioactive element, plays a key role in what we know as H bombs. Not dangerously radioactive for a long period, with a half-life of 12.6 years. But the combination of “H bomb” and “radioactive” tells you why any visit on the ITER site is very closely monitored. And why the ITER organization had to comply with very strict Tritium handling and stocking guidelines, given by the french nuclear authority, itself among the strictest on earth, we were told. A small but significant part of ITER’s huge budgets.

Thank you for reading along, and enjoy life and fusion! And don’t miss the fusion scene in the film Spiderman II. Mr Pitt tried to imitate Dr Octopus with his goggles.


About Jérôme Ducret

Swiss journalist writing in french for two dailies: 24 heures and La Tribune de Genève. Ties with the EPFL and UNIL in Lausanne.