Atomistic Simulations of Displacement Cascades in Fused Silica: It is Compared with Different Concentration of H in the
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0981-JJ07-05
Atomistic Simulations of Displacement Cascades in Fused Silica: It is Compared with Different Concentration of H in the Bulk Fernando Mota1,2, Maria Jose Caturla3, Jose Manuel Perlado1, Angel Ibarra4, and Joaquin Molla4 1 Instituto de Fusión Nuclear, Universidad Politécnica de Madrid. E.T.S.I.I., C/José Gutierrez Abascal nº 2, Madrid, 28006, Spain 2 Ciencias, Universidad Europea de Madrid, C/ Tajo S/Nº Urb. El Bosque, Madrid, 28670, Spain 3 Fisica Aplicada, Universidad de Alicante, Alicante, 03690, Spain 4 Materiales para Fusion, CIEMAT, Avda/ Complutense nº 22, Madrid, 28040, Spain ABSTRACT Amorphous Silica is one of candidate materials for both final focusing optics of lasers for NIF and future inertial fusion reactors and diagnostics of the Safety and Control Systems of the ITER machine as well as DEMO magnetic fusion reactors. In operation, these materials will be exposed to high neutron irradiation fluxes and it can result in point defect and vary the optical absorption, that is, degradation of the optical properties. In this paper we present molecular dynamic simulation of displacement cascade due to energetic recoils in amorphous silica without hydrogen atoms and with 1% of hydrogen atoms trying to identify defects formation. We have made a statistics of the different kind of defects at different energy of primary knock-on atoms (PKA). The range of studied PKA energies are from 400 eV to 3.5 keV and it is made to both component of this material Silicon and Oxygen. We have concluded that three kind of identified defects (Si3, O1, and –OH) are in good agreement with experimental data and the rest of the kind of defect can be related with the three first defects. INTRODUCTION Fused silica has a wide range of applications. The interest on the effects of radiation in vitreous silica has increased recently due to its possible application as optical transmission component in fusion reactors. In this case, this material will be exposed to high neutron irradiation during operation [1,2]. As a result point defects will be created that can lead to obscuration of the material; that is, degradation of the optical properties of silica. Among the defects observed under neutron irradiation are the Oxygen Deficient Centre (ODC), which is related to a silicon atom with coordination three instead of four, and the Non-Bridging Oxygen Hole Centre (NBOHC), which is related to an oxygen with coordination one [3]. In this work we study the production of point defects due to atomic displacements, such as those produced by neutron irradiation. We centre this study in characterizing the types of defects produced during irradiation based on the coordination and potential energy of all the atoms in the simulation box after each collision event. In terms of the applications of interest, namely fusion reactor materials, the most important defect that has been identified experimentally is a colour center in the 248 nm wavelength , which appears under neutron irradiation and makes the material opaque [1, 2], the so-called oxyge
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