Tungsten Blister Formation Kinetic as a Function of Fluence, Ion Energy and Grain Orientation Dependence Under Hydrogen Plasma Environment

• Published in: Journal of fusion energy Vol. 37; no. 2-3; pp. 144 - 153
• Main Authors: Ouaras, K., Redolfi, M., Vrel, D., Quirós, C., Lombardi, G., Bonnin, X., Hassouni, K.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2018; Springer; Springer Nature B.V; Springer Verlag
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ATOMIC FORCE MICROSCOPY; Blistering; Blisters; Chemical and Process Engineering; DENSITY; ELECTRON DIFFRACTION; Energy; Energy Systems; Engineering Sciences; Fluence; GRAIN ORIENTATION; HYDROGEN; Hydrogen plasma; Investigations; Materials; Metals; Nuclear Energy; Nuclear Fusion; Original Research; Physics; Physics and Astronomy; PLASMA; Plasma Physics; Plasmas; SCANNING ELECTRON MICROSCOPY; Size distribution; Sustainable Development; TOKAMAK DEVICES; TUNGSTEN; Hydrogen plasma; Tungsten; AFM; Blister; SEM; Grain orientation; EBSD; Fusion tokamak
• ISSN: 0164-0313; 1572-9591; 1572-9591
• DOI: 10.1007/s10894-018-0161-6

This work deals with the formation kinetic of tungsten (W) blisters under smooth plasma conditions, i.e. low hydrogen flux and energy in order to analyze the first stages of their formation. In addition, we focus on determining the W grain orientation where blisters grow preferentially. For this purpose, mirror-polished polycrystalline tungsten samples were exposed to hydrogen plasma under fixed hydrogen flux of 2.2 × 10 20  m −2  s −1 , with a fluence in the range of ~ 10 24  m −2 , ion energy of ~ 20, 120 and 220 eV, and sample surface temperature of ~ 500 K. The formation of blisters at the surface was investigated using SEM, AFM and EBSD to determine the size, the distribution and the orientation of grain where blisters are formed, respectively. The critical fluence for initiating blisters was established around 2.3 × 10 24 m −2 . The evolution of blister size distribution and density is discussed as function of fluence and ion energy. At lower ion energy, i.e. 20 eV, only nanoblisters (less than 150 nm) are observed whatever the fluence value (1.5 and 2.3 × 10 24 m −2 ). At higher ion energy i.e. 120 and 220 eV, micrometric (~ few to tens of µm) blisters are observed and their density highly depends on fluence. We show that blisters can also be formed on (001) oriented grains contrarily to previous results from the literature where the (111) orientation seemed more favorable. Such information is of importance for tungsten based fusion tokamak operation and design.