The WEST Research Plan was updated in 2022 with the start of phase 2 and the installation of the full ITER-grade divertor. The mission of WEST phase 2 is described in the followong executive summary :
Finding a reliable scheme for power exhaust in magnetic fusion devices has been identified as one of the main challenge towards a future fusion reactor, where the cumulated particle fluence and energy on the plasma facing components will reach unprecedented levels. The divertor is a crucial component for power exhaust in tokamaks, handling the highest heat and particle loads in the vessel, and allowing access to high plasma confinement regimes (H mode).
ITER plans to operate with an actively cooled tungsten divertor over the first ~15 years of its scientific exploitation, for both the Pre Fusion Power Operation (PFPO) phases and the Fusion Power Operation (FPO) phase. The issue of divertor lifetime appropriateness to allow operation until well into the FPO phase with the first tungsten divertor is set as a high priority research area for ITER, given its impact on the ITER Research Plan.
The programme of the WEST tokamak (Tungsten (W) Environment in Steady State Tokamak) is targeted at addressing this issue, minimizing risks for the ITER divertor procurement and gaining experience for its operation. It consists of testing an ITER like actively cooled tungsten divertor under tokamak conditions, taking full benefit of the long pulse capability of WEST, a mega-ampere class superconducting tokamak capable of achieving long plasma discharge (up to 1000s) in a full tungsten environment.
WEST also opens new possibilities to demonstrate the sustainability of plasma scenarios over relevant plasma wall equilibrium timescale (~minutes), as required for steady state operation. Indeed, extending plasma operation to long pulse brings additional constraints (high current drive efficiency, control of MHD at vanishing loop voltage …) and can evidence new issues which do not appear on short pulses, in particular in the field of particle control. WEST provides an opportunity to anticipate current unknowns on the way to long pulse operation in a metallic environment before they are encountered in ITER, and identify solutions.
Finally, WEST features a full tungsten environment, as presently foreseen as a reference option for future fusion reactors, and can therefore handle a number of reactor relevant issues.
The main mission of WEST is twofold and is summarized as follows :
- Paving the way towards the ITER actively cooled tungsten divertor procurement and operation
- Mastering integrated plasma scenario over relevant plasma wall equilibrium time scale in a metallic environment
The high level deliverables expected from WEST include:
- The optimization of industrial scale production processes ahead of ITER divertor procurement
- The assessment of power handling capabilities / lifetime of ITER high heat flux tungsten divertor components in tokamak environment
- A validated scheme for actively cooled metallic plasma facing component protection
- The demonstration of integrated long pulse H mode scenario, including the optimization of RF heating, the control of tungsten contamination and plasma density over plasma wall equilibrium time scale
- The investigation of reactor relevant scenario regimes (such as fully non inductive H mode operation or highly radiating scenario in preparation for DEMO).
For phase 2, the WEST programme retains its integrated structure and is organized around two headlines, aligned with the missions of the European Fusion Roadmap :
- Headline 1 : Plasma regimes of operation
- Headline 2 : Heat exhaust systems
The main blocks of programme have been identified for the two headlines, with associated deliverables, as well as a proposal for priorities and phasing.
After giving feedback on the large scale industrial production of ITER grade plasma facing units (PFU) ahead of the ITER divertor procurement, the scientific programme of WEST for phase 2 will retain its strong focus on preparing for the ITER divertor operation, assessing both how the PFU evolve under plasma exposure in tokamak conditions, and how in turn plasma performance is affected by PFU ageing. A significant effort will be devoted to the development of long pulse operation, integrating issues such as impurity, plasma density or MHD control over time scales relevant for plasma wall interactions (~minutes). In addition, WEST will start exploring alternative scenarios in a full tungsten environment, supporting DEMO conceptual studies. The final phase of WEST exploitation remains open at that stage, in particular to accommodate a number of options for testing innovative reactor oriented technologies, in the field of PFC, diagnostics or heating systems