This paper presents the latest results on confinement studies in the TJ-II stellarator. The inherently strong plasma–wall interaction of TJ-II has been successfully reduced after lithium coating by vacuum evaporation. Besides H retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving special relevance to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 × 1019 m−3 and T e ≈ 250–300 eV, with peaked density, rather flat T e profiles and higher ion temperatures. Due to the achieved density control, a second type of transition has been added to the low density ones previously observed in ECRH plasmas: higher density transitions characterized by the fall in Hα emission, the onset of steep density gradient and the reduction in the turbulence; which are characteristics of transition to the H mode. Confinement studies in ECH plasmas indicate that lowest order magnetic resonances, even in a low shear environment, locally reduce the effective electron heat diffusivities, while Alfven eigenmodes destabilized in NBI plasmas can influence fast ion confinement.

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This paper presents the last results on confinement studies in the TJ-II stellarator. The research of the dependence of spatially resolved transport coefficients on plasma parameters for ECH plasmas with Boronised wall shows that the heat confinement increases linearly with density while particle confinement increases sharply a factor four above a certain density threshold associated with the positive electric field. Remarkably, lowest order magnetic resonances, even in a low shear environment, reduce locally the effective diffusivities. The inherently strong plasma wall interaction of TJ-II has been successfully reduced after Lithium coating by vacuum evaporation. Besides H-retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving especial interest to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 x 10 19 m-3 and Te≈250-300 eV, with peaked density, rather flat Te profiles and increased ion temperatures. Alfvén modes are destabilised and their influence on fast ion confinement is studied in NBI discharges. Due to the achieved density control, a second type of transitions has been added to the low density ones previously observed in boronised wall. The high density transitions, under NBI with Li-coated walls are characterised by the fall of Hα emission, the onset of steep density gradient, and the reduction of the turbulence, which are characteristics of transition to H mode. TJ-II is therefore a unique device where first and second order phase transitions can be investigated.

Water tree length measurementsDuring the growth of water trees in the insulation of a cable the distribution of the electric field is modified because of the local change of the dielectric properties of the material. It results a local enhancement of the electric field which could increase the risk of breakdown. The key factor is the permittivity of the water tree and the aim of the work is to determine its possible values and, particularly, the law of its increase with time during the of the trees. The paper presents permittivity measurements in uniform field in MV and powerThe study was performed using laboratory models made of crosslinked polyethylene and ' we chose the uniform field configurations for several reasons:-a wide deteriorated zone can be generated if

Conductivity () in XLPE insulation of power cables annealed at 90 ºC at temperatures between 50 and 97 ºC has been measured. In all cases there is an initial increase in conductivity that develops a maximum and finally decreases for long annealing times. This maximum appears in the sample annealed 20 days when conductivity is measured at 50 ºC and shifts gradually to higher annealing times up to 40 days when the measurement is performed at 97 ºC. A linear behavior of ln() versus T -1/4 is observed, which implies that the transport mechanism is basically via thermally assisted hopping conduction. Infrared spectroscopy indicates that, during annealing, some chemical species diffuse from the semiconducting shields (SC) into the XLPE. Thermally stimulated depolarization currents technique (TSDC) and intensity-current measurements (I-V) point out as well the presence of this diffusion process that becomes less significant after long annealing times. The initial increase in  is explained in terms of the increase in traps density due to the diffusion process from the SC shields. Long term decrease in  is justified by the observed decrease of diffusion rate for long annealing times.