The Tore Supra tokamak at CEA is famous for its long pulses. In 2003, it set the world record with a plasma lasting for six minutes. Now, 25 years after the first plasma lit up in Tore Supra, the experimental machine starts a new life. It will transform into a test bed dedicated to ITER divertor issues: WEST – Tungsten (W) Environment in Steady-state Tokamak.

WEST fills a gap in the tungsten R&D in Europe as it investigates actively cooled tungsten divertor components in a fusion device. It rounds off the strong R&D programme on tungsten plasma facing components that has been implemented in Europe for more than ten years. Designed for long pulse operation, Tore Supra is the only European tokamak combining superconducting toroidal magnetic field coils, actively water-cooled plasma facing components and adequate additional heating systems. It holds the world record of injected/extracted energy in a one mega-amp class tokamak at a multi-megawatt (MW) level: During a 400 second
plasma pulse, into which three MW of heating power were injected, its plasma facing components removed one gigajoule of energy from the plasma. Tokamak operation with active cooling lies at the heart of the expertise of the Institute for Magnetic Fusion Research (CEA/IRFM). WEST will bring key insights into steady
state operation of a tungsten divertor and its impact on plasma performance. Critical issues are optimisation of the active cooling design, component monitoring during operation, and impact of off-normal events on component ageing.

Modifying Tore Supra

celebrating 25th anniversary of first plasma

In May 2013, CEA celebrated the 25th anniversary of first plasma in Tore Supra. Since its inception, this experimental machine has never ceased to evolve in order to adapt to new scientific and technical challenges and to optimise the performance of the plasmas studied. (From left: Alain Becoulet, Head of the CEA/IRFM, Bruno Ely, curator of the Musée Granet, Michel Chatelier, former Head of the CEA/IRFM). (Picture: CEA)

The WEST project is based on a modification of Tore Supra, transforming it into an X-point divertor device. Thus it will be capable of testing the technologies used for the ITER high heat flux components in relevant plasma conditions. The divertor is a crucial component which must handle the highest thermal and particle loads in the vessel. The ITER full tungsten divertor brings new challenges both in terms of industrial series production of actively-cooled tungsten components and in operation. The WEST project addresses both aspects and is targeted at minimising the associated risks.

The tungsten components to be tested with the WEST platform will be fully representative of the high heat flux flat parts of the ITER divertor plasma facing units. The same technology will be implemented and operated in similar thermal hydraulic conditions as foreseen for ITER (Water pressure and temperature during operation/conditioning: 35/60 bars and 100/200 °C). In addition the modular design of the WEST divertor sectors will offer the possibility to test variants (e.g. detailed design shaping or tungsten grades). The overall number of tungsten elements to be manufactured for WEST represents roughly 15 percent of the amount needed for ITER, which makes the WEST procurement a relevant industrial pre-series, contributing to the optimisation of the series manufacturing process for ITER. The WEST configuration will provide the capability to run long pulses in the high confinement regime (H mode), a plasma operational mode also foreseen for ITER, and test plasma facing components under realistic plasma conditions in terms of pulse duration, heat and particle load.

Works to transform Tore Supra into WEST has begun. CEA has already met one-third of the funding required and is confident that these early successes will bring about the support of other partners and will allow lead to the necessary budget being raised. The internal elements of the Tore Supra tokamak will be modified significantly. A supporting structure for the divertor coils and plasma facing components will replace the Toroidal Pumped Limiter. New components like ICRH antennas, new power supplies for the divertor coils, new diagnostics will be implemented. WEST, which is scheduled to enter into operation in 2016, will provide a key facility to prepare and be prepared for ITER, and is already fully open to international partnerships.

Sylvie Gibert, CEA