WEST concludes the C13 campaign with a major milestone: first H-mode plasmas with ELMs

After nearly three months of experiments, the C13 campaign on WEST has successfully concluded, culminating in the first observation of H-mode plasmas with Edge Localized Modes (ELMs) on the tokamak. This achievement represents an important step in the preparation of plasma scenarios relevant to ITER and future fusion power plants.

For almost three months, scientists, engineers, technicians and operators at CEA Cadarache, together with numerous international collaborators, carried out an ambitious experimental program on the WEST tokamak. The C13 campaign addressed several key scientific and technological challenges for magnetic confinement fusion, ranging from plasma-facing component behavior to advanced plasma scenarios.

The campaign explored tungsten plasma-wall interactions, radiofrequency heating, heat fluxes on plasma-facing components, erosion processes, power balance and plasma diagnostics. These experiments generated a rich dataset that will support the development of predictive models and contribute to the preparation of ITER operation.

The campaign concluded with a particularly significant result: for the first time, WEST produced H-mode plasmas with Edge Localized Modes (ELMs). H-mode is the high-confinement operating regime expected to be used by ITER to achieve its fusion performance objectives. While providing improved plasma confinement, this regime is accompanied by ELMs, bursts of energy and particles released at the plasma edge, which can impose severe thermal loads on plasma-facing components.

Obtaining this operating regime on WEST therefore provides a unique opportunity to investigate plasma-wall interactions closer to foreseen ITER conditions. This achievement opens the route to one of the pilar of the WEST scientific program: testing the ITER divertor components against transient heat fluxes during long time periods, in a tungsten environment similar to the one of ITER. During the final experimental sessions, H-mode plasmas were obtained with separatrix powers between 3 and 3.8 MW and line-averaged densities ranging from 5.4 × 10¹⁹ to 7.2 × 10¹⁹ m⁻³. The ELMs were successfully observed and characterized using several complementary diagnostics, including interferometry, Langmuir probes, and fast visible and infrared cameras.

This milestone follows extensive machine conditioning studies carried out throughout the campaign, including the determination of the minimum wall boronisation needed to restart after a venting, the use of ICRH for wall conditioning between pulses and the use of ICRH for boronisation. Together, these efforts enabled WEST to reach a new operational domain and complete its scientific program.

Beyond this final achievement, C13 demonstrated the strength of the WEST program as an international experimental platform bringing together researchers from CEA-IRFM and partner laboratories worldwide. The results obtained during the campaign will now be analyzed in detail and are expected to contribute to future publications, the validation of plasma-facing component performance, and the preparation of ITER operation.