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| Hauptseite > Publikationsdatenbank > The Impact of Transient Thermal Loads on Beryllium as Plasma Facing Material |
| Hauptseite > Publikationsdatenbank > The Impact of Transient Thermal Loads on Beryllium as Plasma Facing Material |
| Book/Dissertation / PhD Thesis | FZJ-2017-03396 |
2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-227-6
Please use a persistent id in citations: http://hdl.handle.net/2128/15156
Abstract: The rising global energy consumption requires a broad research and development approach in the field of energy technology. Besides renewables, nuclear fusion promises an efficient, CO$_{2}$ free, no long-term radioactive waste producing, and safe energy source using only deuterium and lithium as primary resources, which are widely abundant. However, several technical challenges have to be overcome before a nuclear fusion power plant can be built. For this purpose, the experimental reactor ITER is currently under construction in France. ITER is intended to demonstrate the scientific and technological feasibility of net energy generation via nuclear fusion. The most heavily loaded components inside a fusion reactor, which are directly facing the fusion plasma, have to be armoured with well suited materials, which need to be able to withstand the high thermal and particle loads for an economically reasonable lifetime. For ITER, beryllium is chosen as plasma facing material for the largest fraction of the inner vacuum vessel, the so called first wall. Tungsten will be applied in the bottom region of the vacuum vessel, the so called divertor, which acts as the exhaust system of the machine. The choice of beryllium as plasma facing material was driven by its outstanding advantages, e.g. the low atomic number assures that eroded wall material does not strongly decrease the fusion plasma performance, while it combines a high thermal conductivity with low chemical sputtering characteristics. However, the relatively low melting temperature of beryllium of 1287 °C comprises the risk of amour damage by melting during transient plasma events, such as edge localized modes or plasma disruptions. Even when mitigated, these events put tremendous power densities in the GW m$^{-2}$ range with durations in the ms scale onto the plasma facing materials. Hence, the performance of the ITER reference beryllium grade S-65 under transient thermal loads was studied within this work. Thereby, the focus was set on the understanding of the different damage mechanisms and melting behaviour of beryllium in order to contribute to more reliable performance and lifetime estimations under ITER operational conditions. The transient thermal loads were experimentally simulated in the electron beam facilities JUDITH 1 and JUDITH 2. In the course of the experiments, the absorbed power density, pulse duration, base temperature, number of pulses, and the surface qualities of beryllium specimens were varied to cover a broad range of relevant loading scenarios. With the generated data, a damage map was created showing the surface damages to be expected originating from transient thermal loads with varying absorbed power densities and base temperatures. Furthermore, the damage, cracking, and melting thresholds of beryllium were determined. These thresholds mark the parameter range, in which ITER can be operated without inducing the respective damage type to the first wall. Furthermore, the performance of dierent surface qualities under transient thermal loading was compared in order to determine the optimal surface treatment for the beryllium armour tiles. As a result, the polished and the as received electric discharge machining cut surface qualities exhibited the best performance, while all ground surfaces were severely damaged after 1000 pulses. Hence, grinding of the [...]
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