The heat exchange reduction of tungsten “fuzz” surface irradiated with helium plasma in the PLM device

Abstract

In this work, we measured thermal conductivity of tungsten surface layers grown under helium plasma irradiation in the PLM device at NRU “MPEI”. A stochastic nanostructured fuzz-type surface with fibers of less than 50 nm has grown on the irradiated samples. The duration of discharges in the PLM reached 200 minutes, the thermal load on the surface of the test plates during plasma irradiation was more than 1 MW / m2 and more. Scanning electron microscopy (SEM) analysis revealed the nanostructured fuzz layer of the depth of approximately 1.6 µm on the tungsten exposed to plasma at 950 °C. The density of fuzz layer was observed to depend on the plasma load. We adopted the well-established laser flashing method in order to measure the heat transfer characteristics of tungsten nanostructured surface. Results from measurements show that heat exchange was reduced in the fuzz layers compared to that of pristine tungsten. This reduction can be attributed to the fuzz fibers on the surface.