Irradiation e ects in tungsten under fusion-reactor-relevant conditions

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Title: Irradiation e ects in tungsten under fusion-reactor-relevant conditions
Author: Zitting, Aleksi
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2019
Language: eng
Thesis level: master's thesis
Discipline: Fysiikka
Abstract: Due to increasing energy demand and environmental concerns, developing cleaner and more efficient methods of energy production is becoming more and more important. One such method proposed is a fusion reactor. The plasma facing materials of the reactor must be able to withstand the harsh conditions inside. One such material proposed to be used in constructing the plasma facing components in the reactor is tungsten. In this work I examine the the durability of tungsten under fusion-grade conditions using molecular dynamics simulations. First the impact of neutron irradiation of simulated by simulating 150 keV tungsten irradiation of a 65nm thick tungsten thin film. This was done at 800K and 1900K. After simulating the irradiation event, damage was determined by calculating Wigner-Seitz defects. Larger defect clusters where then analyzed to determine their type. For interstitial type defect clusters loops with the Burger's vector <100> and 1⁄2<111> formed with 1⁄2<111> loops being 4 times as common. For vacancy-type clusters craters, spherical voids and <100> loops formed, however no 1⁄2<111> loops formed even though they are seen in experiments. Temperature didn't seem to have an effect on the amount of defects formed, however the defects that formed were larger at 1900K than at 800K. Secondly the co-bombardment of a tungsten surface with deuterium and a noble gas impurity was simulated. This process was done by randomly selecting either a deuterium ion or a noble gas ion, placing it above the surface and giving it a kinetic energy towards the surface. Several different cases were studied where the following variables were varied: noble gas species (neon or argon), impact energy (10,30,50,80,100 eV), noble gas concentration (5,10,20%) and temperature (500, 800 K). Damage was the determined by looking at the deuterium retention and reflection of the surface, the sputtered tungsten and change of surface morphology. Argon caused more damage than neon. Increasing irradiation energy increased the damage done to the surface, with tungsten sputtering being possible at 80 eV and above. Increased gas concentration also increased the damage. Temperature differences were only significant for deuterium reflection at low energies.

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