Speaker
Description
Ion beam study of plasma interactions with materials in fusion reactors
N. Catarino1, M. Dias1, R. Mateus1, J. Likonen2, A. Widdowson3, E. Alves1
1IPFN, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal
2VTT Technical Research Centre of Finland, PO Box 1000, FIN-02044 VTT, Finlan
3UK Atomic Energy Authority, Culham Science Centre, Abingdon, OX14 3DB Oxfordshire, UK
Accelerator based analytical techniques play a fundamental role on the study of plasma wall interactions in fusion tokamaks. Constant fluxes of energetic neutrals and charged particles lead to erosion and re-deposition processes as well as radiation damage on the walls. In addition, plasma disruptions could cause large thermal shocks melting or vaporizing the material in the chamber walls. In combination with all these effects fuel retention is a process always present which must be fully understood.
In the present contribution, we explore the capabilities of ion beam techniques to study retention and erosion effects of deuterium plasmas in the wall materials of JET tokamak. Samples from different areas of the chamber were analyzed with Rutherford and elastic backscattering spectrometry, nuclear reaction analysis as well as electron microscopy.
Results indicate a major deposition region on the top of divertor tiles (0, 1) with a large retention of 2H. The position of the plasma strike point influences the distribution and deposition in the divertor walls. In the chamber walls the central part of the limiter tiles show an enhanced erosion without no deuterium retention. Retention is mostly observed in the tile gaps and deposition occurs at the ends of the tiles.
Additional studies were performed to get more insight on the effect of the presence of 4He, a fusion product present in the plasma, on the retention properties: With that in mind, we have produced and co-implanted a W-Ta alloy with 4He and 2H. The implantations were done at room temperature with 10 keV of He+ at a constant fluence of 5x 1021 at/m2 and 5 keV of D+ with fluences in the range 1020-1021 at/m2. The results show that the alloys implanted with He+ evidence surface blistering and nuclear reaction analysis shows that D retention is higher after sequential He+ and D+ implantation than for single D+ implantation.
The results will be discussed and a picture of the plasma effects on the chamber walls presented.
