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- Characterization of a single electrode focusing lens for ion beam decelerationPublication . Lopes, Jose; Rocha, J.; Catarino, Norberto; Redondo, LuisAn ion beam deceleration system was studied for the highcurrent ion implanter at the Laboratório de Aceleradores e Tecnologias de Radiação at the Campus Tecnológico e Nuclear, of Instituto Superior Técnico. The installed system consists of a target plate and one electrostatic focusing lens with one electrode. This article describes the results of the evaluation of the new system. With this upgrade, the ion implanter provides enhanced versatility for decelerating to 5 keV a high current ion beam at the µA level. This implantation provides a wide area and allows for a continuous magnetic beam scanning, extending the energy range to lower values, opening up a wider set of applications.
- 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.
- Very high fluence nitrogen implantations in metals studied by Rutherford Backscattering SpectrometryPublication . Cruz, João; Silva, Hugo; Lopes, Jose; Rocha, J.; Pedro De Jesus, AdelaideThis paper reports a study of 14N+ implanted Ti and Zr films analysed by Rutherford Backscattering Spectrometry (RBS). The fluences ranged from 4.0–10.0 × 1017 atoms·cm−2 and energies of 15–20 keV. Here, the nitrogen depth distributions were obtained simultaneously and independently for each RBS spectrum from the direct nitrogen signal and from the reduction of the backscattered yield from Ti and Zr (deficiency method). Fits to the RBS spectra show that the deficiency method clearly underestimates the 14N yield by 32% for Ti (and 45% for Zr) when compared to the direct nitrogen signal. This discrepancy reduces to 23% for Ti (and 43% for Zr) when the presence of nitrogen bubbles are simulated in the fits.
- Conversion system for grid-to-vehicle and vehicle-to-grid applicationsPublication . Marinho, Diogo; Chaves, Miguel; Gamboa, Paulo; Lopes, JoseThe increasing use of electrical vehicles aroused the problem of batteries charging and the consequent interface with the power grid. Commercial charging solutions are mostly based on unidirectional power flow converters; however, bidirectional power flow converters are an interesting solution when considering smart microgrid applications, with benefits in efficient energy use. In this context, the paper presents a bidirectional power flow converter for grid-to-vehicle (G2V) or vehicle-to-grid (V2G) applications. The conversion system is based on a three-phase voltage source inverter (VSI), which assures the grid connection with a unitary power factor. The direct current (DC) bus of the voltage source inverter is connected to a DC/DC converter that controls the battery power flow. This conversion system can operate in G2V mode when charging the battery or in V2G mode when working as an energy storage system and the power flow is from the battery to the power grid. The conversion system model is presented as well as the control strategy proposed. Simulation and experimental results showing voltages and currents in the circuit are also presented.