Electrochemical noise (EN) measurements were carried out to study the effect of turbulent flow conditions on corrosion kinetic of API X60 pipeline steel weld immersed in synthetic seawater. In order to control the hydrodynamic conditions, two rotating cylinder electrodes were used. The EN data were analysed by three different statistical methods: currents transients, noise resistance and localisation index (LI). On the other hand, the spectral method was used in order to get the noise impedance. The superficial analysis using a scanning electron microscopy was carried out. According to EN analyses, the current transients indicate that the aggressiveness of the corrosion increased as the rotation speed also increased. The highest corrosion rate values were obtained at turbulent flow conditions. In the superficial analysis, a localised corrosion form was found in all corrosion processes; these results are agreed with the results obtained by LI.

The insulating materials for radio frequency (RF) windows and different antenna supports for heating systems and some diagnostics are still an unresolved issue in future fusion machines such as DEMO. Alumina ceramic (Al 2 O 3 ) is one of the main candidate materials for these systems. The dielectric properties, such as electrical permittivity (ε) and loss tangent (tanδ), determine its power losses. Therefore, tanδ values need to be low, between 10 -6 and 10 -3 depending on the application. However, due to the crucial role of the manufacturing process in determining its final dielectric properties, there is the need to undertake a joint effort with the industry in order to validate a standard manufacturing route that ensures a supply of ceramic material with homogeneous and standardized dielectric properties for future fusion machines.In DEMO, these ceramic materials will be operated under extreme conditions. They will be exposed to considerable levels of neutron irradiation. Radiation Induced Conductivity (RIC) and Radiation Induced Electrical Degradation (RIED) are phenomena that influence notoriously on the dielectric performance of these materials. Therefore, their optimum properties must be tested under relevant irradiation conditions. Hence, it is important to accurately characterize their dielectric properties before irradiation to be able to compare them with the future post neutron irradiation results. Furthermore, other types of radiation such as beta and gamma are also used in the irradiation scheme to provide more information on the variation of dielectric properties of ceramics due to radiation effects.In this work, loss tangent and permittivity values of some pre-irradiated candidate materials will be presented as well as the measuring techniques used at CIEMAT. These techniques have the advantage of covering a very broad range of frequencies required for alumina applications in fusion (from kHz to GHz) and giving the best accuracy for very low losses.Keywords: fusion, DEMO, ceramics, dielectric properties, Rafael Vila, INTRODUCTIONThere are several material issues that need to be addressed before the construction of future fusion reactors such a DEMO. In particular, materials chosen for radio frequency (RF) windows and different antenna and diagnostics supports, as well as insulators for the heating systems are not still fully defined. The systems in which the materials are going to be used operate in three main frequency ranges related to the main heating systems: 40-80 MHz for Ion Cyclotron Heating, 1-15 GHz for Lower Hybrid Current Drive, and 100-250 GHz for Electron Cyclotron Heating. Some of the diagnostics will also require insulators that work at lower frequencies. The dielectric properties, such as electrical permittivity (ε) and loss tangent (tanδ), determine the power losses in the materials. The losses would produce high temperature gradients that could cause material fracture due to mechanical stress. Mechanical and thermal properties need to be studied as well; however, in this case, ...

The electrochemical studies of the corrosion can provide indirect techniques that they can determinate the corrosion rate of metals or alloys immersed in a corrosive medium. For many years, most studies about the cathodic and anodic polarization behaviour of metals have been confined to traditional steady-state techniques, such as potentiodynamic sweep measurements. However, steady-state techniques are limited because they give information only on the ratedetermining step. Moreover, during the measuring process, technique such as potentiodynamic sweep polarize the electrode surface to such a great extent, in order to uncover corrosion mechanism, that the validity of the results can be questioned particularly in the cases when protective films. Transient electrochemical techniques such as Electrochemical Noise (EN), are less intrusive because they can provide information about the processes without disturbing the reactions with the voltage application.