Evolution of pre-damaged ITER grade plasma facing components under WEST plasma exposure: smoothing and tungsten sources

Nuclear Fusion, vol. 64, pp. 106002

Abstract

Abstract The evaluation of the impact of plasma-facing units (PFUs) damage on subsequent plasma operation is an important issue for ITER. This is one of the topic addressed by the operation of dedicated PFUs in WEST. From the start of WEST in 2017, few ITER grade divertor PFUs were tested in the lower divertor for short plasma exposure (experimental campaigns C1–C5). A PFU is an assembly of tungsten blocks on CuCrZr tube via pure copper interlayer. Since 2022, WEST operates with a lower divertor fully equipped with ITER grade PFUs (experimental campaign C6–C7) with long duration plasma exposure capabilities. To test the ageing of the ITER-grade PFUs on an accelerated basis, well controlled damage was implemented on purpose with electron beam loading on the plasma facing surface of two different PFUs (pre-damage#1 and #2 featuring different level of damage). Damage tackled in this study is induced by the loading with numerous transient heat loading events to mimic the ELM impact on the ITER grade PFU. This paper presents the damage before and after WEST plasma exposure and shows the tungsten sources and temperature of the block measured during the operation. On damaged area, surface roughening is heterogeneous. With WEST campaigns (C3, C4 and C7) respectively ended in (2018, 2019 and 2023) a global smoothing of the pre-damaged surfaces, in particular those located in the high loaded erosion area, is observed. No evolution of the crack is observed in the electron beam loaded area, while new cracking are observed on non pre-damaged area on the tungsten top surfaces in highly loaded areas (outer strike point) after significant plasma duration and cumulated energy (first observation in C4 and tends to be confirmed with preliminary observations after the C7 campaign). Smoothing is less pronounced after the 2018 campaign, which may be due to the related short plasma duration. The surface smoothing of blocks also depends on their poloidal position. For PFU which has no shaping, toroidal positioning within a block has no influence on the surface smoothing. After 2019 and 2023 campaigns, equivalent relative smoothing is obtained (between 19 and 32%). For the explored plasma conditions, damage has no influence on the maximum brightness of W.

Authors 15

1. M. Richou corresponding

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

2. Yann Corre

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

3. Mathilde Diez

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

4. A. Durif

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

5. C. Guillemaut

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

6. Q. Tichit

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

7. Emmanuelle Tsitrone corresponding

   Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Cadarache

   Affiliation as printed

   CEA IRFM, Saint-Paul-Lez-Durance, France

8. Daniel Dorow‐Gerspach

   Forschungszentrum Jülich

   Affiliation as printed

   Forschungszentrum Jülich GmbH, IEK-4, Jülich, Germany

9. Th. Loewenhoff

   Forschungszentrum Jülich

   Affiliation as printed

   Forschungszentrum Jülich GmbH, IEK-4, Jülich, Germany

10. M. Wirtz

    Forschungszentrum Jülich

    Affiliation as printed

    Forschungszentrum Jülich GmbH, IEK-4, Jülich, Germany

11. Alex Grosjean

    University of Tennessee at Knoxville

    Affiliation as printed

    The University of Tennessee Knoxville, Knoxville, TN, United States of America

12. Céline Martin

    Centre National de la Recherche Scientifique · Aix-Marseille Université

    Affiliation as printed

    Aix-Marseille University, CNRS, PIIM, Marseille, France

13. G. Giacometti

    Centre National de la Recherche Scientifique · Aix-Marseille Université

    Affiliation as printed

    Aix-Marseille University, CNRS, PIIM, Marseille, France

14. Anke Aretz Aachen Central Facility for Electron Microscopy

    RWTH Aachen University

    Affiliation as printed

    Central Facility for Electron Microscopy, RWTH, Aachen, Germany

15. J. Gaspar

    Centre National de la Recherche Scientifique · Aix-Marseille Université · Institut Universitaire des Systèmes Thermiques Industriels

    Affiliation as printed

    Aix Marseille University CNRS, IUSTI, Marseille, France