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The ionization effect on both the evolution and internal structure of a blast wave (BW) is determined in laboratory conditions. In a first step, the Rankine–Hugoniot equations describing the structure of the shock front together with the Saha equation modeling ionization are solved analytically in a consistent way for the conditions of a cold initial atomic hydrogen gas. In a second step, a simplified approach is used by introducing an effective adiabatic index γ * that takes into account ionization arising at the shock front. Finally, γ * is used as input data in the self-similar model derived formerly by Barenblatt to describe the structure and the dynamics of the ionizing BW. For the typical laboratory conditions of blast wave experiments, ionization achieves a hydrogen gas compression up to about 11 times at the shock front of the blast wave where a thin and dense shell forms. For such a compression, the value of the effective adiabatic index is γ * ≃ 1.2 leading to a self-similar evolution of the BW where its radius R(t) varies according to R ( t ) ∝ t α * with α * ≃ 0.33. This value of α * is lower than the adiabatic expansion stage α = 2 / 5, where the total energy of the BW is conserved. Thus, ionization is found to act as a cooling effect at the shock front where a fraction of kinetic energy is absorbed to ionize the gas.

The self-similar study of cooling blast waves (BWs) is performed for the case of a homogeneous self-similar cooling of the gas. This analysis is crucial to better understand its internal structure and global evolution when the BW loses a significant amount of energy due to cooling processes. The evolution of the shock front radius Rsh follows the law Rsh(t) ∝ tα where the decelerating parameter α covers the range 1/4 ≤ α ≤ 2/5 depending on the magnitude of the cooling rate. When the cooling is negligible, α = 2/5, and we recover the analytical solution of Sedov-Taylor (ST) where the total BW energy is conserved. For the internal structure of the cooling BW, we demonstrate that there exist two types of solutions. The first type is the ST-type solution, which is smooth until the center of the BW and only exists for 1/4 < α′ ≤ α ≤ 2/5, where α′ is a specific value of α. This special solution is determined through an eigenvalue problem. The second type is a shell-type solution where a thin cooled shell is bounded by a contact discontinuity separating the shell from a hot rarefied interior bubble where the pressure is homogeneous. The shell becomes thinner and denser when the cooling rate increases. For a strong enough cooling rate, the density inside the shell can diverge at the contact discontinuity while the temperature goes to zero.

Partial modeling of the hydrodynamic evolution of the supernovae is one of the prominent applications of laboratory astrophysics. In particular the role of Rayleigh–Taylor instability (RTI) in supernova evolution needs to be explained. In this paper we analyze the compressibility effects on the RTI in the linear regime. We compare the compressible isothermal and stratified incompressible RTI growth rates and analyze the vorticity generation at the interface. We show that for several configurations the effect of compressibility can be significant in supernovae remnants.

The interaction of the mixing zone between two gases of different densities with compression waves and shock waves has been investigated. The characteristics of the mixing zone in which the Rayleigh–Taylor instability is developing have been analyzed. The evolution of the mixing zone volume and mass during the accelerated motion has been defined. A qualitative distinction in the evolution of the mixing zone under the influence of a continuous deceleration resulting from the interaction with the reflected compression wave—shockless deceleration—is revealed as compared to deceleration that is accompanied by appearance of a shock wave moving through the mixing zone—shock-induced deceleration.

We use analytic self-similar solutions of both the linear and non-linear diffusion equation to determine the behavior of a heat conducting system experiencing a time-dependent energy production. Supposing a power law evolution of the system parameters, we calculate the corresponding exponents to describe the temporal behavior of the system. In the non-linear case, we are able to introduce a variation of both the coefficient of diffusion and the amplitude of the heat source. The analytic solutions are checked numerically. These results can be considered, for example, as the basis for further developments on the non-linear behavior of supercritical fluids in a microgravity environment, e.g. the “Piston Effect” (M. Bonetti et al., Phys. Rev. E 49 (1994) 4779) or the “Jet Instability” (D. Beysens et al., Near-critical Fluids in Space, in: Lectures on Thermodynamics and Statistical Mechanics, M. Costas et al., eds. (World Scientific, Singapore, 1994) p. 88).

International audience; In this paper, experimental results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Two sets of experiments have been performed at the Laser pour l'Utilisation des Lasers Intenses (LULI) laboratory. Several shock parameters were simultaneously measured: shock temperature and velocities, the precursor two-dimensional (2D) time evolution, its electron density, density gradient, and temperature. Data were obtained varying initial conditions for different laser intensities and gas pressures. Comparisons with 1D and 2D radiative hydrodynamic simulations are shown for all measured parameters (shock velocity, shape, radial expansion, and temperature as well as precursor velocity and electron density).

This paper studies the effect of a nonstationary shell acceleration on the development of the Rayleigh-Taylor instability (RTI) in supernovae remnants (SNRs). Two groups of solutions describing acceleration and deceleration phase of the SNR shell are obtained. Using a special transformation (co-moving coordinate frame), an exact dispersion relation for nonstationary RTI is derived. It is shown that compressible and incompressible branches are separated for the spherically symmetric flow and only the former is unstable. The exact analytic solution is compared to a simpler WKB-like analysis and a good agreement is shown, which proves that this analysis can be useful and easily extended to further applications.

Two different methods giving non destructive depth information in Auger Electron Spectroscopy (AES) are described, (i) The first one is based on the Auger ratio PB (ratio of the Auger peak to the background at the same energy). In the case of a binary alloy XY, and as soon as the Auger electron mean free paths of the two elements are sufficiently different, it is possible to obtain a depth information by plotting (PB)x versus (PB)y (ii) The second one is more general and uses the ratio of the Auger tail height (T) to the Auger peak height (P). This ratio (TP) is independent of the concentration of the element. It is only dependent on its depth distribution. Both methods are applied to the experimental example of a silver deposit on a Si(111) surface.

Through rescaling and obtaining invariant equations, we study the expansion of charged particles immersed in a time-varying magnetic field B(t) = B0(1+Ωt)–β. We develop the theory for a configuration of point particles confined in a plane with an initial cylindrical symmetric configuration. It is found that the system expands according to (1+Ωt)2β/3 for β ≤ 1 and it is conjectured that in a properly rescaled space and time, it reaches asymptotically an inhomogeneous (in space) Brillouin flow with rigid rotation at half the cyclotron frequency (ω = ½ωc). Particular attention is given to the ‘pivot’ case β = 1. It is shown then that the radius of the rescaled configuration is now dependent on the ratio Ω/ωc, and grows indefinitely with time for Ω/> 3.2–3/2;. Numerical experiments are presented which confirm these theoretical predictions and conjectures. Finally, the properties of this system are compared with those of single-particle and ‘rod’ electrostatic models.

During heating, a TiAl alloy becomes covered by elemental sulphur and chlorine which remain segregated at the surface after cooling. Auger electron spectroscopy has shown that the chlorine disappears progressively with time at room temperature, while the sulphur is not removed. Experiments have been performed which show that the disappearance of chlorine is due to electron bombardment and that chlorine is expelled only locally from a zone around, and considerably larger than, the area of beam impact. We suggest that chlorine escapes from the impact area by superficial diffusion and not by electron-stimulated desorption. The influence of various parameters, such as the properties of the electron beam and the temperature of the sample, have been studied in an attempt to explain the observed electron beam effect.

We seek a generalization of the derivation by Lewis and Leach for invariants quadratic in p. Since the general equations for invariants cubic and quartic in p cannot be solved, we specialize to self-similar solutions of the equations. Consequently, we can recover only a part of their solutions for quadratic invariants, but new pairs of potentials and invariants are obtained, where the leading term in the invariants is p3 or p4. More precisely, all the potentials are of the form V(q, t) = At2λ-2(q/tλ)ν + B(λ)q2/t2, where ν is prescribed and A is arbitrary. Different functional forms for B lead to different families of solutions where, for each family, the parameter λ is allowed to go from −∞ to +∞. Finally, a generalization to potentials with three terms is given.

The Auger signal is defined as being the ratio, in the direct mode, of the height of the Auger peak to the background at the same energy. This Auger signal is shown to be an intrinsic measurement, proportional to the volume fraction of a given element in the sample. It is in a very large degree independent of the instrumental parameters adjustment, except for the primary beam energy. Provided the respective mean free paths of the Auger electrons are sufficiently different, it is even possible to acquire a precise information on the depth distribution of the elements.

If the Auger ratio is defined as being the ratio of the Auger peak to the background at the same energy, this Auger ratio can be considered as an intrinsic measurement, characteristic of the sample, and in a very large degree independent of the instrumental parameters adjustment: intensity of the primary electron beam, modulation voltage, Wehnelt voltage, focusing, deflection, sample positioning, electron multiplier gain and further amplification. However, this Auger ratio depends on the primary electron energy. In a specimen homogeneous in depth, the Auger ratio of an element X normalized to that obtained on a pure X sample yields a direct measurement of the volume fraction occupied by that element in the sample. It is no longer necessary to normalize an Auger peak to the sum of all the other peaks, or to resort to the ratio of the peaks on a given spectrum. Providing that the respective mean free paths of the Auger electrons are sufficiently different, it is even possible to acquire a valuable information on the depth distribution of the elements.

Small quantities of silicon improve the intergranular corrosion resistance of nickel in sulphuric acid, except for diluted alloys (0 to 2 at% Si) where the increasing corrosion is attributed to silicon segregation [1,2]. We have used Auger electron spectroscopy (AES) in the En(E) mode for segregation studies and described the utilization of the peak-to-background ratio (PB) for quantitative analysis [3]. First we report the silicon behaviour at free surfaces of alloys and the influence of cosegregated impurities (mainly sulphur) on equilibrium coverage. After some annealing treatments, samples were broken in high vacuum and AES analyses of grain boundaries were performed and compared to free surface results.