The presence of materials with a relative large difference in permeability has a harmful influence on the convergence of Krylov subspace iterative solvers. Some slow converging components are not cured by preconditioning and correspond to eigenvectors reflecting the domains with relatively low permeable material. Approximations for those eigenvectors are determined using physical knowledge of the problem. The iterative solution process is split up in a small problem counting for the separated eigenmodes and a full-size problem out of which the slow converging modes are removed. This deflated preconditioned solver is faster converging compared to more common approaches, such as the incomplete Cholesky conjugate gradient method.

The magnetic circuit of power transformers is built with magnetic oriented grain sheet. These modern sheets present a more and more narrow static hysteresis cycle, as well as an important remanent flux density, generally larger than 1 tesla. Although such a magnetic circuit necessarily includes joint air gaps, the experiment shows that these don't lead to an appreciable weakening of remanent fluxes. In order to explain the “paradox” of the existence of an important remanent fluxes in the magnetic circuits including air gaps, we propose a new model of joint called "pseudo-variable air gap" allowing to account for the nature of the type of joint: butt or overlap. It is shown that the new model fully explains the existence of an important remanent when the overlap joint has been used (which corresponds to the power transformer case), as well as the nearly total disappearance of the remanent fluxes in case of butt type joint. In addition, this model could be easily implemented in a global transformer model; which contributes to the improvement of the transformer models deriving from the circuit theory.

One of the main research issues in the thermonuclear fusion area is the identification of plasma contour starting from external magnetic measurements. Possible approaches to this inverse problem make use of equivalent currents to represent the plasma internal current density, regularizing in this way the magnetic field reconstruction. Of course, the choice of the representation basis for such equivalent currents is critical. The paper aims at analyzing the effect of the number and position of base currents on the performance of the identification algorithm.

In this paper we have studied the contribution of electrostatic and magnetic turbulence on particles anomalous transport in the tokamak. The diffusion coeffficient is evaluated. Comparison between diffusion magnetic field lines and particles is carried out. We also treat the effects of the reversed shear barrier in reducing the particles anomalous transport in the tokamak.

The study of forces exerted by an arc on silver-based electrical contacts is important in order to understand the dynamic phenomena concerning the opening or closing phases of contacts in a variety of switching applications. For that, an experimental device was built. It allows us to measure accurately the force on the static electrode and the displacement of the mobile electrode (and hence the force on it) when the two contacts, crossed by a current pulse (from 0 to 4 kA) separate. The measured forces are the sum of Lorentz magnetic forces (constriction force and loop effect force) and blow open forces due to the arc plasma (evaporation and (or) decomposition of contact materials). A simple method allowed us to asses the value of the blow open forces. We have also studied the influence on the measured forces of the contact material, the amplitude of the current pulse, the polarity of the electrodes. For the electrode materials tested in this study (Ag-SnO2, Ag-CdO and Ag-CW), it appeared that forces exerted on cathode and anode are of the same order and that AgSnO2 use allows to have higher forces (and longer opening phase) than for the two other materials and then may decrease the contact welding.

We have designed and built a liquid helium immersion insert which is magnetically shielded from the ambient magnetic field fluctuations by the use of a superconducting lead can. The insert has a variable temperature stage made of sapphire which is optically heated by the light guided from an external lamp via a glass rod. The temperature regulation is achieved by the use of a commercial PID controller: the temperature of the sapphire ranges from 50 K to 100 K with peak to peak fluctuations less than 20 mK over a 3 minutes observation period. The magnetic noise inside the insert has been measured with a low Tc dc-SQUID and the white noise level above 200 Hz is less than 4 fT/$\sqrt{\rm Hz}$. Furthermore, the magnetic attenuation factor due to the superconducting lead can is greater than 26 500 for frequencies above 15 Hz. This cryogenic insert is used for studying low frequency vortex noise in high Tc superconducting thin films at different temperatures and the field penetration in the films as a function of the applied magnetic field during its transition state.

This paper presents a model taking into account moving bodies. An electrodynamic device which consists of a magnet over a superconductor shall be examined. In order to determine the mechanical behaviour of the device a coupled solution of the electromagnetic and the mechanical problem is used.

A systematic parameters study is performed in a DC pulsed glow discharge in nitrogen in order to improve the wettability of thin polystyrene layers. The experimental parameters considered are the pressure P, the interelectrode voltage V, the frequency ν of the pulsed power supply and the treatment time tt. The wettability is characterized by the contact angle technic. The $(\Theta_{\rm i} - \Theta_{\rm f})/\Theta_{\rm i} = \Delta \Theta / \Theta_{\rm i}$ ratio is measured, where $\Theta_{\rm i}$ and $\Theta_{\rm f}$ are respectively the initial and final contact angles. In the first part of the paper, the variations of $\Delta \Theta / \Theta_{\rm i}$ as a function of the electrical energy E are investigated, the variations of E being obtained by modifying the parameters V, ν and/or tt. In the second part, the specific energy ε and the economical criterion γ are introduced to deduce the best running conditions through a chemical engineering approach. Taking into account the weak duty factor of the power supply (1% ), it is shown that the polymer surface is treated with a minimum of energy.

When performing the analysis of electromechanical transient problems with movement, it is needed to take into account the air gap deformation with time. A new remeshing procedure is proposed. It is based on node displacements coupled to a Delaunay algorithm. The node movement is described using bubbles in association with a physical model. The procedure generates high-quality meshes.

Optically pumped magnetometers are scalar magnetometers which are particularly suitable for mobile applications for which it is necessary to use an isotropic sensor. Our group has recently designed a new helium magnetometer with reduced sensor orientation effects. In this paper, we present the results about frequency spatial isotropy and show frequency effects smaller a 240 pT.

Continuum-mechanic derivations of the entrainment of rarefied gases induced by a surface acoustic wave (SAW) along the wall in a confined microtube are conducted by the perturbation method. Both no-slip and slip flow results are presented with the former ones matched with the previous approach by Yin and Fung. The critical reflux pressure-gradient values decrease as the Knudsen number increases from zero. Meanwhile, the (perturbed) mean flow induced by SAW along the wall of a microtube is proportional to the square of the wave-amplitude ratio which has been confirmed by previous experiments.