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EEE4.07 - Characterisation of Helium-Implantation-Induced Changes in Tungsten for Fusion Applications 
April 23, 2014   10:45am - 11:00am

Fusion energy has the potential to provide a sustainable, environmentally friendly and almost inexhaustible long-term energy source. One of the main obstacles on the path to commercial magnetic confinement fusion reactors is the availability of sufficiently resilient materials. Plasma facing components will be exposed to high operating temperatures (>1300 K), bombardment with energetic particles (up to 20 MWm-2) and intense irradiation with 14.1 MeV fusion neutrons up to total doses of tens of displacements per atom (dpa). Some of the harshest conditions will be experiences by the divertor, which functions as the exhaust for helium produced in the fusion reaction. Currently the main candidate materials for the divertor plates in ITER are tungsten and its alloys due to their high melting point, good resistance to sputtering, high thermal conductivity, low tritium retention rate, and stability under irradiation. During operation of the divertor, large amounts of helium are deposited near the material surface, whilst in the bulk helium is generated by transmutation. As such it is vital to understand the modifications that occur in tungsten due to the presence of helium.We have used synchrotron X-ray micro-beam Laue diffraction to quantify the lattice swelling associated with helium-implantation in a tungsten, 1% rhenium alloy. Using density functional theory (DFT) calculations we estimate the volume of formation of different helium-associated defects in tungsten. By comparing simulations and experimental measurements we estimate that approximately one third of the implanted helium is located at interstitial sites, whilst the remainder is confined in substitutional helium defects. Based on this we predict the anticipated changes in elastic modulus associated with the retained helium.

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Panel Discussion - Different Approaches to Commercializing Materials Research
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Fred Kavli Distinguished Lectureship in Nanoscience
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