E×B probe measurements in the plasma plume of a 100 W-class Hall thruster

International audienceThe ion far-field plume of the 100 W-class ISCT100-v2 Hall Thruster (HT) has been characterized by means of an E×B probe. The influence of operating parameters on both velocities and fraction of different ion species was investigated over a 40 • circular arc. E×B spectra were thus recorded for different background gas pressures, discharge voltages, angular positions and propellants (namely xenon and krytpon). The probe alignment is also discussed in this contribution, since measurements were recorded for the probe aligned with both the thruster centerline and the thruster mid-channel

Effects of the α-ε phase transition on wave propagation and spallation in laser shock-loaded iron

International audienc

Response of iron to two symmetric laser shocks

–Laser-driven shocks provide a means of studying the dynamic behaviour of solid materials at very high strain rates. Here, we investigate the effects of a new pulsed load, generated by the crossing of two symmetric laser shocks. Both surfaces of thin iron foils are irradiated simultaneously by two high-power laser beams, producing two compressive pulses of duration about 3 ns and amplitude about 10 to 60 GPa. When they cross each other in the central region of the sample, considerable increases of the pressure and the temperature are induced, leading to twin formation and phase transition. Then, the interactions of all the incident and reflected release waves which propagate inside the sample result in various types of spall damage, depending strongly on the sample thickness and on the shock pressure. All those effects have been observed in the recovered targets, and explained by a phenomenological analysis of wave propagation. The influences of various experimental parameters have been investigated. Finally, one-dimensional computations have been performed to test the ability of a simple constitutive model, including twin formation, phase transformation and spallation, to predict the observed results. A rough agreement between computations and experiments, better at lower shock pressure, bas been obtained

Laser shock techniques to investigate shock-induced phase transitions in quartz

The very short duration of laser shocks and their low-destructive character provide new means of studying the kinetics of phase transitions. Here, we investigate the phase transformation behavior of quartz under dynamic compression of short duration (nanosecond order) generated by various laser shock techniques. VISAR measurements have been performed to characterize the stress history induced in the targets. Recovered samples have been analyzed by micro-Raman spectroscopy. The influences of several experimental parameters (pulse duration, tensile and shear stresses...) have been investigated. The results, which differ notably from observations reported under quasi-static compression or longer pulsed loads (microsecond order), suggest a partial amorphization of the shocked samples, as well as the formation of a new structure that can be compared to known orthorhombic high pressure phases

Laser-driven shocks to study phase transformations in materials of geophysical interest

International audienc

Multi-criteria decision analysis and ecosystem services:Knowledge gaps and challenges for policy and decision-making

The identification of ecosystem services (ES) and their valuation for potential use in environmental, social and political decision making is a fast growing research area. The ES literature is growing exponentially from less than 200 papers per year at the beginning of the Millennium to over 1600 per annum at the moment. While the ability to identify, classify and quantify ecosystem services has greatly improved and there is some movement towards unification of techniques, the hoped-for increased use in practical decision making has lagged severely behind. One reason for this is a slower integration of the resulting (ES) information with the type of multi-criteria decision support (MCDA) methods appropriate for issues with large numbers of criteria, both qualitative and quantitative, and large number of alternative options to be considered. The required techniques exist, (e.g. AHP, concordance, etc.) and are well known in the MCDA domain, but cross-fertilisation between the two scientific domains has been slow. This paper first summarises the established systems for classifying ecosystem services and then explores the issues relating to incorporating ES into a MCDA framework. When controversy arises and decisions are likely to be challenged, politically and legally, their underpinning by an accepted, rigorous and scientific methodology is important.</p