When electron beams are directed against solid targets (unsupported thin film, bulk or surface film) some particles come back and emerge from the surface. These particles are not reflected without dissipation of energy because of their penetration below the surface and the resulting loss of small amounts of energy by ionizations, electrons excitations, plasmon emissions and so on. In this paper the fractions of electrons backscattered from surface films with various thicknesses deposited on different substrates, calculated by using both an analytical approximation (Multiple Reflection Method) and a numerical approach (Monte Carlo) are presented. The results of the two approaches are compared. The analytical method results are also compared with experimental data concerning surface films and good agreement is found between theory and experiment. The comparison allows us to conclude that the proposed analytical method, keeping in mind the underlying approximations, represents a useful and informative approach.

Nowadays, the switched reluctance machine are widely used. To determine their performances and to elaborate control strategy, we generally use the linear analytical model. Unhappily, this last is not very accurate. To yield accurate modelling results, we use then numerical models based on either 2D or 3D Finite Element Method. However, this approach is very expensive in terms of computation time and remains suitable to study the behaviour of eventually a whole device. However, it is not, a priori, adapted to elaborate control strategy for electrical machines. This paper deals with a non linear analytical model in terms of variable inductances. The theoretical development of the proposed model is introduced. Then, the model is applied to study the behaviour of a whole controlled switched reluctance machine. The parameters of the structure are identified from a 2D numerical model. They can also be determined from an experimental bench. Then, the results given by the proposed model are compared to those issue from the 2D-FEM approach and from the classical linear analytical model.

This paper presents some results from experiments carried out on a flyback converter whose transformer has been built with a new stress-annealed nanocrystalline (iron-based) material developed by our laboratory team. This original process has provided a low value of relative permeability (around 200) at a high induction level, thereby making it possible to store large amounts of energy. A flyback transformer without air-gap was thus tested in order to evaluate the performance of this material, with highly satisfactory results being obtained. Because of the material's low magnetic losses at a high induction level and high-frequency switching (up to 25 kHz), low transformer losses along with a low temperature rise were observed. A figure of merit is proposed in order to situate our material performances among others.

In this paper a method is proposed in order to obtain an interval of possible values for the surface power density brought to the electrodes by an electric arc of short duration and short electrode gap. Two examples of results (for a copper anode and a copper cathode) are presented in the case of an electric arc in air at atmospheric pressure.

The spatiotemporal relaxation of electrons in spatially one-dimensional plasmas acted upon by electric fields is investigated on the basis of the space- and time-dependent electron Boltzmann equation. The relaxation process is treated using the two-term approximation of an expansion of the electron velocity distribution function in Legendre polynomials. To verify the complex Boltzmann equation approach by a completely independent kinetic method, results for inhomogeneous column-anode plasmas of glow discharges between plane electrodes are compared with corresponding ones obtained by Monte Carlo simulations. The spatiotemporal electron relaxation in argon plasmas, subjected to a space-independent electric field and maintained by a time-independent inflow of electrons at the cathode side of the plasma region, is considered. Starting from steady state at a given electric field, the relaxation process is initiated by a pulse-like change of the electric field strength and is traced until the spatially structured, time-independent state associated to the changed field is reached. The behaviour of the velocity distribution function and macroscopic quantities of the electrons in space and time is analyzed for enlarged and reduced electric field strengths typical of the column region of glow discharges. In particular, the spatiotemporal reformation of plasma structures has been found to progress in two phases, i.e., existing structures in the distribution are driven to merge in wide plasma region first, followed by a formation phase of new spatial structures which are induced by the cathode-sided inflow of electrons. The results for the macroscopic quantities and the isotropic distribution functions obtained by Boltzmann and Monte Carlo calculations agree very well during the spatiotemporal transient process as well as in the new steady state finally reached.

An experimental study of Marangoni flows in horizontal layers of tin based metallic alloys heated from the side is carried out, based on the observation of the motion of tracer particles at the surface associated with a direct measurement of temperatures in the melt. A key feature of the procedure is that the experiments are performed in a high vacuum environment to limit as much as possible the pollution of the liquid vapour interface. In pure tin, depending on the intensity of the driving force measured by the Reynolds-Marangoni number, either viscous or boundary layer flow regimes are found. In addition, the onset of temperature oscillations is found to be consistent with the hydrothermal wave instability mechanism proposed by Smith and Davis. In tin-bismuth alloys, the observed flow directions and velocities are interpreted in terms of a non linear dependence of the surface tension on temperature, and successfully compared with the dependence predicted by interpolating the available experimental surface tension data with the help of a simple thermodynamic model. During the directional solidification of the layer, the concentration gradient in the solute rich boundary layer ahead of the growth front is found to locally modify the flow pattern. For instance, when thermal and solutal driving forces act in the same direction, temperature oscillations are observed at low values of the Reynolds-Marangoni number. As for opposing driving forces, the situation is that a local reversal of the flow direction is observed in correlation with the morphological instability of the growth front.

A monochromatic Fe beam is generated by heated supersonic expansion of argon seeded with Fe vapor. At a nozzle temperature of 1930 K and 800 torr argon inlet pressure the Fe beam has an axial velocity spread of 8% and intensity of 3 × 1015 s−1 sr−1, corresponding to a deposition rate of 10 nm/h at 150 mm from the nozzle. The two-chamber alumina crucibles are chemically stable for liquid Fe. With 400 mm3 Fe we have operated for more than 200 hours without reloading. The power consumption at 1930 K is 750 W. Temperature stability at constant power (without feedback) is better than 30 K. The source is intended for deposition of nanostructures by laser focusing of the Fe beam. The small axial velocity spread virtually eliminates the increase in focal spot size due to chromatic aberration.