WEST tungsten contamination issues and proposed solutions in support to ITER

WEST (tungsten –W– Environment in Steady-state Tokamak) is a device specialized for long pulse operation in a tungsten environment. It is mainly electron heated with strong current drive capabilities. One of the main purposes of WEST is to support ITER operation and to address relevant physics issues, especially plasma-wall interactions in a metallic environment. In the first part of this contribution, we describe the WEST plasma reconstruction workflow based on IMAS (Integrated Modelling and Analysis Suite). This workflow runs after each plasma discharge and allows dependency management of around 50 diagnostics. WEST pioneers the use of IMAS for its data management, a unique opportunity to test IMAS and give feedback to ITER.

In a second part, we discuss the main issues related to tungsten contamination during WEST phase 1 and 2. The main novelty of phase 2 is the use of actively cooled ITER-grade mono-blocks for the divertor. During both WEST phases, core tungsten profiles are rather flat, nonetheless burning through tungsten is challenging in the power ramp-up phase. In this contribution, we propose a strategy to efficiently burn through tungsten and increase plasma robustness. In parallel, we show encouraging results about the development of non-inductive scenarios; more than 100 second plasmas have been achieved. Finally, we report on the recent development of the X-point radiator scenario. This scenario provides at the same time low divertor heat fluxes and improved plasma confinement. WEST confirms the good properties of this scenario, making it a clear candidate for ITER high power operation.