Effects of porosity on surface chemistry, wetting, and percolation in porous tungsten, liquid lithium hybrid plasma facing component system

Tungsten continues to be the material of choice for plasma facing components (PFC) in the divertor region of future plasma-burning fusion nuclear devices due to favorable properties such as high melting point, high thermal conductivity and low sputtering yield. However, challenges remain for the use of monolithic tungsten under future fusion reactor-relevant conditions including enhanced hydrogen retention, surface cracking and surface morphology evolution that may lead to macro-level impurity emission into the plasma. An alternative approach to conventional monolithic tungsten-based PFC materials is to introduce designs to mitigate known shortcomings of tungsten. This work explores the concept of protecting the plasma from high-Z material emission by integrating a low-Z component that is in the liquid phase. Plasma-surface interaction properties of a porous tungsten-liquid metal hybrid system, having the favorable bulk thermomechanical properties of W while serving as a scaffold for a liquid metal with self-healing and radiative vapor shielding characteristics, is examined. W-substrates with 70% density of bulk W and 1-5m sized pores have been fabricated with 50-nm W powders using spark plasma sintering. Lithium surface chemistry was observed to change in favor of forming Li-O-D as opposed to lithium oxide. Enhanced lithium wettability driven by percolation through the porous tungsten architecture is demonstrated with in-situ liquid lithium drop measurements. Results show complete wetting of liquid Li at 250C in the porous W, 100C lower temperature than what has been observed on traditional tungsten surfaces. Accompanying experiments using in-operando 7.2keV O3+, 8.9keV O4+ ERD in the DIONISOS platform, capable of 1020 m-2s-1, demonstrate Li signals as deep as one micron indicating percolation during exposure to a 250eV/amu D+ plasma. The results presented here demonstrate the feasibility of incorporating, a liquid metal into a porous tungsten substrate, both in wetting and percolation. Furthermore, this integration has shown some favorable PMI characteristics, such as the potentially controllable retention of deuterium Li-O-D.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2019

Author dc:creator

• Kapat, Aveek S.

Contributors dc:contributor

• Allain, Jean Paul
• Andruczyk, Daniel

• Porous tungsten, liquid lithium, wetting, percolation, lithium chemistry

Statement dc:rights

• Copyright 2019 Aveek Kapat

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/105103

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/105103