WEST — W Environment in Steady-state Tokamak, after tungsten's chemical symbol — is the superconducting 📝Tokamak operated by the CEA's Institute for Magnetic Fusion Research at Cadarache in southern France, rebuilt from Tore Supra to test 📝ITER-grade 📝divertor components under sustained heat load. It took first 📝plasma in December 2016.
Tore Supra, operating from 1988, was already unusual in two respects that made it the right machine to convert: superconducting 📝toroidal field coils and actively cooled 📝plasma-facing components, the combination required for pulses measured in minutes rather than seconds. The WEST conversion added what Tore Supra lacked — an 📝X-point and a real divertor — by installing up-down symmetric, fully 📝tungsten, water-cooled divertor assemblies and reshaping the plasma to an elongated ITER-relevant cross-section. Published parameters are a major radius of 2.5 metres, a minor radius of 0.5, a 📝toroidal field of 3.7 📝tesla and a 📝plasma current between 0.5 and 1 megaampere, with the coils rated for pulses up to 1,000 seconds.
The machine's purpose is duration under load, not fusion gain: it burns no tritium and makes no claim on 📝Q. Its first operating phase, 2017 to 2020, integrated ITER-grade divertor prototypes, coupled up to 8.8 megawatts of 📝RF heating, and reached divertor heat fluxes of 6 megawatts per square metre. On 12 February 2025 WEST held a plasma for 1,337 seconds — about 22 minutes, and the longest tokamak discharge on record, exceeding the previous mark set on 📝EAST by roughly a quarter.