Abstract
Gross and net erosion of tungsten (W) and other plasma-facing materials in the divertor region have been investigated in deuterium (D) and helium (He) plasmas during dedicated experiments in L- and H-mode on ASDEX Upgrade and after full-length experimental campaigns on the WEST tokamak. Net erosion was determined via post-exposure analyses of plasma-exposed samples and full-size wall components, and we conclude that the same approach is applicable to gross erosion if marker structures with sub-millimeter dimensions are used to eliminate the contribution of prompt re-deposition. In H-mode plasmas, gross erosion during ELMs may exceed the situation in inter-ELM conditions by 1–2 orders of magnitude while net erosion is typically higher by a factor of 2–3. The largest impact on net erosion is attributed to the electron temperature while the role of the impurity mixtures is weaker, even though both on ASDEX Upgrade and WEST significant amounts of impurities are present in the edge plasmas. Impurities, on the other hand, will lead to the formation of thick co-deposited layers. We have also noted that with increasing surface roughness, net erosion is strongly suppressed and the growth of co-deposited layers is enhanced. In He plasmas, gross erosion is increased compared to D due to the higher mass and charge states of the plasma particles, resulting from larger energies due to sheath acceleration, but strong impurity fluxes can result in apparent net deposition in the divertor. Our results from ASDEX Upgrade and WEST are comparable and indicate typical net-erosion rates of 0.1–0.4 nm s−1, excluding the immediate vicinity of the strike-point regions.
Highlights
Tungsten (W) and tungsten-based alloys are promising candidate materials for plasma-facing components (PFCs) in future fusion reactors [1,2,3], largely due to their small erosion yields by physical sputtering, high melting point and large thermal conductivity, as well as low retention of radioactive tritium (T) and other hydrogen isotopes of the plasma fuel in W
Gross and net erosion of tungsten (W) and other plasma-facing materials in the divertor region have been investigated in deuterium (D) and helium (He) plasmas during dedicated experiments in L- and H-mode on ASDEX Upgrade and after full-length experimental campaigns on the WEST tokamak
The largest impact on net erosion is attributed to the electron temperature while the role of the impurity mixtures is weaker, even though both on ASDEX Upgrade and WEST significant amounts of impurities are present in the edge plasmas
Summary
Tungsten (W) and tungsten-based alloys are promising candidate materials for plasma-facing components (PFCs) in future fusion reactors [1,2,3], largely due to their small erosion yields by physical sputtering, high melting point and large thermal conductivity, as well as low retention of radioactive tritium (T) and other hydrogen isotopes of the plasma fuel in W. Understanding the physics mechanisms influencing erosion and retention behaviour of tungsten PFCs has been high in the priority list of the European fusion research programme under the EUROfusion Consortium, both with the help of dedicated experiments and using interpretative numerical simulations [4] In this contribution, we report on recent experimental activities related to distinguishing the balance between the gross and net erosion of W in a tokamak, i.e. how material is primarily released into the edge plasma via sputtering and how it is subsequently migrating and re-depositing in the reactor vessel.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
