Recent research and development of thick CVD tungsten coatings for fusion application

Abstract

As the interface closest to the edge plasma of a fusion reactor reacting deuterium (D) and tritium (T), plasma-facing material (PFM) need to withstand extreme service conditions with the high particle flux, high heat load, and neutrons with energy up to 14.1 MeV. Tungsten (W) is the primary candidate of PFMs in future fusion reactors due to its high melting point, good thermal conductivity, excellent irradiation resistance, and low hydrogen/helium retention. So far, powder metallurgy is a leading route for the preparation of W-based PFM. An alternative approach could be the coating technique, which has advantages on fabricating W PFMs and plasma-facing component (PFC) simultaneously. In the past several years, inspiring results were achieved in the preparation process and performance evaluation of the W coating with high purity, excellent thermal conductivity, and thickness at the millimeter level by atmospheric pressure chemical vapor deposition (APCVD). No obvious grain growth and hardness decrease were observed when the annealing temperature was lower than 1500 °C, indicating its good thermal stability. The as-deposited coating exhibited a comparable thermal shock resistance with the conventional W bulk. While the polished sample showed a high crack threshold (0.33–0.44 GW·m−2) when exposed to edge localized mode like transient at room temperature, compared to the unpolished counterpart. Irradiation performance of the chemical vapor deposition (CVD)-W exposed to deuterium (D) plasma and fission neutron were also evaluated. Additionally, the practicality of preparation of large-scale W-based PFM by this technique is also demonstrated. This paper gives a short overview on the recent research and development status of the thick W coating prepared by APCVD at Xiamen Tungsten Co., Ltd and Southwestern Institute of Physics for using as PFM and PFC in fusion devices.