In-situ LIBSi rakendamine ITERisse sobilike materjalide uurimiseks

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Üheks lahenduseks inimkonda ohustavale energiakriisile on tuumasüntees, millel on klassikaliste energiatootmise viisidega võrreldes mitmeid eeliseid. Praegu ehitatakse Prantsusmaale esimest tuumasünteesireaktorit ITER (ing k International Thermonuclear Experimental Reactor). Esimene plasma plaanitakse reaktoris tekitada juba 2020. aastal, kuid üheks lahendamist vajavaks küsimuseks on reaktori seinte seiramine. Paratamatult puutub ülikuum (100000000 oC) plasma reaktori seintega kokku. Selle käigus toimuvad muutused seinte struktuuris ning reaktori kütus (vesiniku isotoobid deuteerium ja triitium) salvestub seintesse. Reaktori järjepideva ning ohutu toimimise tagamiseks on tarvis pidevalt jälgida seinte seisukorda ning määrata ka seintesse salvestunud radioaktiivse triitiumi hulk. Üheks perspektiivikaks meetodiks on laser-indutseeritud plasma spektroskoopia (LIBS): uuritava objekti pinnale fokusseeritakse lühike intensiivne laservälge. Tekib plasma, mille kiirguse põhjal määratakse objekti koostis. Meetodil on mitmeid eelised: see on kiire, proove pole tarvis ette valmistada, neile pole vaja isegi füüsiliselt ligi pääseda. Doktoritöös uuriti LIBSi rakendatavust ITERis kasutatavate materjalide analüüsiks. Uuritavad materjalid olid volfram ja alumiinium. Neist viimast rakendati ITERis reaalselt kasutatava berülliumi aseainena. Töös uuriti LIBS plasma dünaamikat ning valiti välja analüüsiks sobivad volframi spektrijooned. Vaadeldi ka volframi pinnastruktuuride mõju salvestatavale spektrile. Töö käigus seati LIBS seade üles lineaarsetele plasmaseadmetele Hollandis DIFFER instituudis. Need seadmed võimaldavad mõjutada proove plasmaga, mis sarnaneb ITERis seina tabava osakestevooga. Sellega demonstreeriti, et LIBS on sobilik ekspressmõõtmistes madalatel rõhkudel. LIBSi abil mõõdeti nii volframkihtide paksuse vähenemist kui ka proovidesse salvestunud deuteeriumi hulka. Meetodi rakendamiseks ITERis on vaja teha veel täiendavat uurimistööd, kuid näidati, et LIBS on sobilik diagnostikameetod plasmaseadmetes.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 Experimental Reactor) 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