Kaarel Piip will defend his doctoral thesis titled „Development of LIBS for in-situ study of ITER relevant materials” on 16 June 2016 at 14.15 at W. Ostwaldi 1, room B103.
Matti Laan, Institute of Physics, University of Tartu
Peeter Paris, Institute of Physics, University of Tartu
Pavel Veis, Comeniuse University, Slovakia
Summary: Nowadays the need for new energy sources is one of the most crucial problems. Compared with traditional ways of energy production, the using of nuclear fusion has several advantages. The first fusion reactor ITER (International Thermonuclear ExperimentalReactor) is under construction in France. The first plasma is planned in 2020. One problem which still needs a proper solution is the online monitoring of the reactor walls. Due to the instabilities, the extremely hot plasma hits the reactor walls. During this interaction the material of the walls is eroded and its structure may change and the fuel (hydrogen isotopes deuterium and tritium) are retained in the walls. For the sustainable and safe operation of ITER, the walls have to be monitored and the amount of radioactive tritium in the walls has to be measured. One strong candidate for these measurements is laser-induced breakdown spectroscopy (LIBS). A short and intensive laser pulse hits the studied surface and plasma is formed. The plasma radiation is recorded to determine the composition of the object. LIBS has a number of benefits: it is fast, there is no need for sample preparation and only optical access to the sample is needed.
In the PhD thesis the applicability of LIBS for analyzing ITER-relevant materials was studied. Tungsten and aluminum containing samples were tested. Aluminum was used as a proxy for the beryllium. LIBS plasma dynamics was studied and a set of suitable tungsten spectral lines was selected. The relation between sample surface structures and the recorded LIBS spectra was also described.
LIBS setup was installed for the linear plasma devices in FOM Institute DIFFER (The Netherlands). These devices enable to expose the samples with plasma fluxes that are comparable to the ones will occur in ITER. The decrease in the thickness of tungsten layers and the amount of deuterium retained in the samples was successfully measured. Although further research is needed to apply LIBS in ITER, this work demonstrated that LIBS is a suitable monitoring method in plasma devices.