On the other side of the CEA fence, in Cadarache, sits a large tokamak which played an important role in the definition of ITER.
Tore Supra, a CEA-Euratom device which began operating in 1988, was the first tokamak to successfully implement superconducting magnets and actively-cooled plasma-facing components.
Over the past twenty-four years, Tore Supra has explored the physics of long-duration plasma pulses, reaching a record of 6.5 minutes in December 2003.
In 2000-2002, Tore Supra was equipped with a new carbon-carbon fibre (CFC) "limiter"—the equivalent of the divertor in ITER—capable of withstanding an ITER-relevant heat load of 10 MW per square metre.
This project, named CIEL for Composants Internes Et Limiteurs, demonstrated that, while CFC performs very well in terms of power handling and compatibility with the plasma, its use results in substantial erosion caused by the physico-chemical reactions between the carbon of the limiter and the hydrogen (deuterium) in the plasma. Further experiments in JET have confirmed these observations.
Now, there are not many options when it comes to choosing the material of a divertor. Fifty years of experience in tokamak technology have narrowed the choice to two: it's either CFC or tungsten. Their respective advantages or disadvantages depend on the plasma regimes they are exposed to (more
here).
In ITER, it was originally planned to begin operations with a CFC divertor and replace it with a tungsten one before the start of nuclear operation (deuterium + tritium) in 2027. After years of discussions, panels and reviews, a new plan was established and ITER is now considering doing without the first-phase CFC divertor.
Indeed, substantial cost reductions would be achieved by installing a tungsten divertor right from the start and operating it well into the nuclear phase. This solution would also provide for an early training, during the non-nuclear phase of ITER operation, on how to operate with a tungsten divertor.
The ITER Members, however, have not yet reached a unanimous position on this issue.