ISEL - Eng. Electrotécn. - Artigos
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Browsing ISEL - Eng. Electrotécn. - Artigos by Author "Alves, E."
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- Helium and deuterium irradiation effects in tungsten-based materials with titaniumPublication . Catarino, Norberto; Dias, Marta; Lopes, Jose; Jepu, Ionut; Alves, E.Pure Tungsten (W) will be used as plasma facing component in fusion devices due to its high melting point, good thermal conductivity and low sputtering yield. However, its structural application as plasma facing component (PFC) is still restricted by its low fracture toughness associated with the high ductile to brittle transition temperature (DBTT). In the present study tungsten titanium (W-Ti) samples were produced by Ti implantation at room temperature and 500 °C with a constant fluence of 2 × 1021 at/m2 and an energy of 100 keV. In order to understand the fundamental mechanisms which govern the behavior of defect dynamics in tungsten under reactor conditions, W-Ti materials were implanted at room temperature with 10 keV of He+ with a constant fluence of 5 × 1021 at/m2 and 5 keV of D+ with fluences in the range of 0.1 × 1021–5 × 1021 at/m2. Surface structure and morphology changes were investigated by scanning electron microscopy and X-ray diffraction. Rutherford backscattering spectrometry, nuclear reaction analysis and thermal desorption spectroscopy methods were used to provide information about the distribution of Ti, He and D on W. No changes in the microstructure were observed after Ti implantation in the W plates. NRA analysis showed that D retention in the W-Ti samples is higher after sequential He and D implantation when compared with single D implantation. The diffractogram of W-Ti samples implanted with He evidence a broadening of the W peaks. This effect is believed to be associated with the high volume fraction of the bubbles that may cause internal stress fields inducing extended defects like dislocations which distort the crystal lattice.
- Mass spectrometry improvement on an high current ion implanterPublication . Lopes, J. Gabriel; Alegria, F. C.; Luis Redondo; Rocha, J.; Alves, E.The development of accurate mass spectrometry, enabling the identification of all the ions extracted from the ion source in a high current implanter is described. The spectrometry system uses two signals (x-y graphic), one proportional to the magnetic field (x-axes), taken from the high-voltage potential with an optic fiber system, and the other proportional to the beam current intensity (y-axes), taken from a beam-stop. The ion beam mass register in a mass spectrum of all the elements magnetically analyzed with the same radius and defined by a pair of analyzing slits as a function of their beam intensity is presented. The developed system uses a PC to control the displaying of the extracted beam mass spectrum, and also recording of all data acquired for posterior analysis. The operator uses a LabView code that enables the interfacing between an I/O board and the ion implanter. The experimental results from an ion implantation experiment are shown. (C) 2011 Elsevier B.V. All rights reserved.