In ITER, it was originally planned to begin operations with a primarily CFC divertor and replace it with a full tungsten divertor before the start of nuclear operation (deuterium + tritium) in 2026 (now 2027). After years of discussions, panels and reviews, a new plan was proposed 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 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.

Beginning with a carbon material was considered to have several advantages for the start of ITER operations, given its proven range of compatibility with a number of plasma conditions in present devices, particularly at low densities with significant additional heating. Its use would considerably ease the development of techniques for the control and mitigation of plasma instabilities (Edge Localized Modes and disruptions) which, even in the lower power conditions characteristic of the non-active phases of ITER operation, can generate heavy heat pulse transients. Unlike carbon, which sublimes, tungsten melts and there was a real concern that the very short duration, high heat fluxes that can be deposited during these transients could yield deformations of the precise material surfaces, compromising subsequent operation. Largely due to the high level of tritium retention expected as a consequence of fuel co-deposition with carbon eroded from divertor target surfaces, ITER intended to replace the first carbon/ tungsten divertor with an all-tungsten variant before the start of the deuterium and deuterium-tritium plasma operation phases. However, the required high heat flux tungsten technology had never been tested in the demanding environment of a tokamak under the steady state plasma heat fluxes (~10-20 MW m-2) expected on divertor surfaces during ITER fusion plasma operation. Moreover, the fabrication of the ITER divertor with full-tungsten armor in the high heat flux strike point regions, represented an unprecedented technological challenge.

For the past two years the Joint European Torus (JET) facility has been strongly focussed on the issues associated with ITER design choices and the preparation of ITER operation, as have other tokamaks around the world. To this end, the materials of the plasma facing components (PFCs) in JET were replaced with the same combination foreseen in ITER, namely a combination of Be for the main wall and the possible use of tungsten for the divertor. The installation of the "ITER-like wall" required more than 3000 tiles to be fitted by remote handling manipulators and interfaces. In addition to the new wall, JET installed several upgrades to active protection systems and diagnostics, vertical stability control and heating capability with an increase of the routinely-available neutral beam power up from 20 MW to 30 MW. The on-going studies and results obtained so far are providing important data to the ITER design team and have demonstrated agreement with hoped-for expectations.

The French superconducting tokamak, Tore Supra, which has been operating on a site adjoining the ITER site since 1988, is also focused on providing data for ITER materials choices. It 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 composite (CFC) "limiter" - the equivalent of the planned first phase 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 confirmed these observations.

A feasibility study named 'WEST' (acronym derived from W Environment in Steady-state Tokamak, where W is the chemical symbol for tungsten), was launched on 25th February 2010, aimed at getting answers in a timely manner for the then-planned second phase divertor for the (nuclear) phase of ITER. Alain Bécoulet, the Head of CEA-IRFM (Institut de Recherche sur la Fusion Magnétique) which operates Tore Supra, says, "By installing an ITER-like full tungsten divertor in Tore Supra, we can turn our platform into a test-bench on ITER critical path. We can thus contribute to reducing the risk and to saving time and money for ITER." Adapting Tore Supra to accommodate a full tungsten divertor - 500 components with a total of 15,000 tungsten tiles - is a challenge the Institute is ready to take on, says Bécoulet, (All carbon will have to be taken out of the device; in-vacuum vessel magnetic coils will need to be installed in order to modify the plasma shape from circular to "D-shaped" and heating systems will have to be adapted to the new configuration.)

The formal decision to proceed with the WEST project on Tore Supra is due to be taken at the end of 2012.