[en] Today, air pollution is monitored using static stations and modelling, which provides valuable information to document air pollutant levels. Nevertheless, there is still a lack of knowledge about personal exposure, especially regarding indoor air quality. Therefore, the ANR-Polluscope project (2016-2020) aims to track air pollution all day long (indoor and outdoor) by equipping volunteers with small air quality sensors in order to monitor the air we actually breathe. Target pollutants are black carbon, particulate matter (PM), NOx , ozone and VOCs. The first step of the project is to select and assess the sensors to be used, before to launch real measurements campaigns with volunteers. The results of these tests are presented here and include three testing stages. First, static measurements tests were performed to compare small sensors results with reference instruments. Then the sensors were tested into a controlled chamber in order to test their performance when environmental conditions (for instance humidity) vary suddenly. Finally, mobility tests were carried out, people wore the sensors all day long to measure the ability of the micro units to be efficient in real campaign conditions.

[en] Collective (or coherent) Thomson scattering has recently emerged as an important tool for identifying and characterizing certain instabilities in Hall thrusters. Plasma instabilities in electric thrusters are implicated in diverse phenomena, including reduced efficiency, lifetime and anomalous particle transport. This work discusses the main features of the collective scattering diagnostic PRAXIS, and recent applications of the diagnostic to study the nature of microturbulence at different thruster operating regimes. Early measurements show the presence of a small-scale azimuthal instability may be linked with regimes of unstable thruster operation

[en] Microwave beam backscattering near the cut-off layer appears to be the most interesting diagnostic to observe density fluctuation time evolution for a given localization in the plasma and at a defined wave vector. It also provides perpendicular plasma velocity. Scattering only occurs when the Bragg selection rule is fulfilled, i.e. when the scattering wave vector is almost perpendicular to the magnetic field. In order to evaluate these scattering conditions, ray tracing is required. 3D geometry is necessary to evaluate the angle between the magnetic field and the wave vector at the reflection. The ripple effect on the iso-index layer curve cannot be neglected. Scattering localization and wave vector resolution can be approached if single ray tracing is replaced with quasi-optical beam tracing. Optical propagation is still considered in the WKB approximation but the beam is described as multiple connected rays. The beam radial expansion due to diffraction is well described. This approach allows one to compute beam parameters for all data acquisitions (50 triggers per shot) and all shots (40 shots per day) during the following night on a recent personal computer with MatLab (copyright)

[en] The effect of the ergodic divertor on the plasma edge in Tore Supra is to enhance the perpendicular transport through ergodization of the magnetic field lines [Ph. Ghendrih et al., Contrib. Plasma Phys. 32 (3 and 4) (1992) 179]. Nevertheless, the hot spots observed on the divertor plates during ergodic divertor operation indicate that the cross-field transport driven by the fluctuations is still playing an important role, although measurements by CO₂ laser scattering and reflectometry show a decrease of the turbulence level [J. Payan, X. Garbet, J.H. Chatenet et al., Nucl. Fusion 35 (1995) 1357; P. Beyer, X. Garbet, P. Ghendrih, Phys. Plasmas 5 (12) (1998) 4271]. In order to gain more understanding, fluctuation level and poloidal velocity have been measured with a reciprocating Langmuir probe biased to collect the ion saturation current (j_sat) and with a CO₂ laser scattering diagnostic. Though the relative fluctuation level behaves as previously observed at low density, a new interesting result is that this picture is gradually modified when the density is increased. Both diagnostics observe an increase of δn/n with density in the ergodic region, which is not the usual behavior observed in limiter configuration. This increase is detected on both sides of the E_r inversion radius and is therefore also affecting the plasma bulk. Finally, the confinement time is found to follow an L-mode law at all densities indicating that the ergodic divertor does not change the global confinement properties of the plasma

[en] Collective scattering measurements have been conducted on the plasma of a Hall thruster, in which the electron density fluctuations are fully characterized by the dynamic form factor. The dynamic form factor amplitude distribution has been measured depending on the k-vector spatial and frequency components at different locations. Fluctuations are seen as propagating waves. The largest amplitude mode propagates nearly along the cross-field direction but at a phase velocity that is much smaller than the ExB drift velocity. Refined directional analysis of this largest amplitude mode shows a thin angular emission diagram with a mean direction that is not strictly along the ExB direction but at small angles near it. The deviation is oriented toward the anode in the (E,ExB) plane and toward the exterior of the thruster channel in the (B,ExB) plane. The density fluctuation rate is on the order of 1%. These experimentally determined directional fluctuation characteristics are discussed with regard to the linear kinetic theory model and particle-in-cell simulation results.

[en] Collective light scattering (CLS) has been applied for the study of density fluctuations in diverse plasmas. In tokamaks, it has been used to obtain correlations between microturbulence and the quality of energy confinement in thermonuclear fusion plasmas. It has also been used in the study of the ionosphere. Apart from plasma studies, CLS has also been exploited for several years in the study of aerodynamic turbulence. CLS has been recently extended to the observation of Hall effect thruster plasmas. The origins of thruster phenomena such as anomalous electron transport are still to be determined. A CLS diagnostic has been developed for measuring electron density fluctuations in the thruster, at millimeter length scales and MHz frequencies. Fluctuations at these length and time scales have been predicted to play a role in anomalous transport. Collective scattering experiments have provided information on dispersion relations and the directionality of different types of fluctuation modes at the predicted scales. Such information has allowed confirmation of certain aspects of linear kinetic theory and provided new information on the modes which will enable their role in transport to be more carefully evaluated. This document is composed of the slides of the presentation

[en] Full text: There are two prevailing approaches to confinement prediction for future devices such as ITER. The first, whose accuracy is rather limited, is to extrapolate global empirical scaling laws to these devices. The second approach, which is in principle more sound, is to use first principle models such as gyrokinetic simulations in integrated modelling. In this latter approach, validation of physics ingredients of these codes against experimental measurements is of critical importance. With this motivation in mind, dedicated dimensionless scan experiments have recently been performed on Tore Supra to investigate the impact of rhostar and nustar on transport and general turbulence characteristics. The present paper focuses on the impact of changing nustar on wavenumber spectrum and on phase velocity of density fluctuations measured using Doppler backscattering system. High resolution measurements exhibit perpendicular wavenumber spectra following a power law with a spectral index equals to -3 at low k and starting to decrease much faster for higher k. At basic level, the form of the k-spectrum appears to be robust and all spectra measured on Tore Supra are well represented by an exponential function or by a function derived from a simple drift wave turbulence model with disparate scale interactions. However, we show that the collisionality affects the shape of the spectra: parameters of both functions depend significantly on nustar pointing to the possibility of a transition in the turbulence regime. In addition to the wavenumber spectrum, Doppler backscattering system grants access to mean perpendicular velocity of density fluctuations which is the sum of the phase velocity of density fluctuations and of the mean ExB rotation. The dependence of mean perpendicular velocity of density fluctuations with the perpendicular wavenumber gives an indication about the dispersion relation since the mean E x B velocity is independent of the wavenumber. It is found that in the high nustar discharges, the mean perpendicular velocity of density fluctuations decreases with increasing k while there is no clear dependence on k for the low nustar discharges. The existence of these two different forms may correspond to a transition between two modes with different dispersion relations as well as between a pure and a mixed mode. (author)

[en] Comb reflectometers offer the advantage of measuring several radial positions in plasma simultaneously. This allows for the investigation of fast timescales during L-H transitions, I-phases, I-mode bursts, transients during heat wave propagation, etc. A drawback of many present-day systems is that they use a fixed frequency difference between the probing frequencies. Hence, although the central probing frequency can be varied, the probing frequency difference is usually fixed. The new design presented in this work uses an advanced microwave generation and detection scheme, which allows for arbitrary probing frequencies and probing frequency separations. (paper)

[en] The effect of the collective light scattering diagnostic transfer function is considered in the context of the dispersion relation of the unstable E×B mode previously reported. This transfer function is found to have a contribution to the measured frequencies and mode amplitudes which is more or less significant depending on the measurement wavenumbers and angles. After deconvolution, the experimental data are found to be possibly compatible with the idea that the mode frequency in the jet frame (after subtraction of the Doppler effect due to the plasma motion along the thruster axis) is independent of the orientation of the wave vector in the plane orthogonal to the local magnetic field.

[en] On Tore Supra, the frequency spectra of the turbulent fluctuations often have two peaks centred on some positive and negative values. These two peaks correspond to a poloidal motion of the electrons in opposite directions. In this paper, a criterion is elaborated which allows us to distinguish, in time, the density fluctuations convected in the parallel direction from those in the anti-parallel direction with respect to the analysing wavevector. Two signals are thus extracted out of one. The validity of our model is experimentally checked by comparing the auto-correlation coefficients and the frequency spectra computed for the whole and the separated signals. Consequently, the frequency spectrum is studied in detail as a function of the analysing wavenumber leading to an accurate determination of some plasma properties. (author)