Development and Performance of Tungsten-Coated Graphitic Foam for Plasma-Facing Components

Abstract

High-density graphitic foam is an ideal low-Z plasma-facing material for deuterium-deuterium plasma experiments where tritium codeposition is not an issue. However, like all carbon, graphitic foam suffers from a precipitous drop in thermal conductivity at high temperatures, >600°C. To mitigate these problems, functionally graded layers of tungsten can be deposited to a thickness of 2 to 4 mm onto the plasma side of the foam using chemical vapor deposition. The graphitic foam then acts as a high-conductivity heat sink at temperatures below 600°C for the thin high-Z armor coating. The overall component weighs 18 times less than a comparable volume of tungsten and lacks the coefficient of thermal expansion joining issues between the CuCrZr tubing and the tungsten. This paper discusses the coating development and characterization and presents the results of recent plasma exposures in W7-X. It also reports on computational fluid dynamics heat transfer modeling and preparations for high heat flux testing of mock-ups. This hybrid plasma-facing component (PFC) consisting of innovative engineered materials may be a cost-effective, actively cooled solution for the divertors and other PFCs in long-pulse machines like W7-X and WEST.

Keywords:

• Graphitic foam
• tungsten
• coating
• divertor
• plasma-facing component

Acknowledgments

We gratefully acknowledge the contribution of C. Parish at ORNL for pre-exposure SEM characterization. We also wish to thank D. Wolfe, T. Medill, and G. Showers at ARL for HHF testing. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under contract number DE-AC05-00OR22725. Work in the European Union has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training program 2014–2018 and 2019–2020 under grant agreement number 633053. This manuscript has been authored by UT-Battelle, LLC under contract number DE-AC05-00OR22725 with the U.S. Department of Energy.