The properties of the tungsten coating on fine grain graphite using pulsed laser deposition

Abstract

The advantages of using a high-Z material as a plasma facing component (PFC) in fusion devices is now admitted, consequently, the International Thermonuclear Experimental Reactor (ITER) will have a solid tungsten divertor. In this article, we present the properties of tungsten coating on fine grain graphite using the pulsed laser deposition (PLD) technique. We successfully achieve a uniform coating without cracks nor gaps while maintaining a low level of oxygen impurities in the deposited layer of about 1%. The coating shows tensile stresses as the body centered cubic (BCC) crystal structure of tungsten adapts to the graphite hexagonal structure. We use the Williamson-Hall method to distinguish the contributions of crystallite size and strain on the broadening of the X-ray diffraction peaks; The former increases from 30 to 50 nm while the latter saturates around 2.5 × 10−3 with increasing PLD laser energy. The Rutherford backscattering spectrometry (RBS) analyses show that the coating thickness is about 120 nm for PLD laser energy below 500 mJ. Around this value, the thickness increases abruptly to 300 nm and remains almost unchanged up to 600 mJ. © 2019 Elsevier B.V.