Characterization of diamagnetism inside an ECR thruster with a diamagnetic loop

The plasma-induced magnetic field in an electron cyclotron resonance plasma thruster is measured non-intrusively by means of a diamagnetic loop that encloses the plasma flow. The calibration process is described, and parasitic currents in the thruster walls and plasma oscillations are identified as the dominant sources of uncertainty. The integrated magnetic flux is seen to depend on the applied power and less significantly on the mass flow rate. The effect of the diamagnetic loop radius is also studied by testing two loops of different diameters. To estimate the perpendicular electron pressure in the plasma from the loop measurements, two plasma beam models, 1D and 2D, are used. While both models give similar results for the small loop, they differ significantly for the large loop, showing the relevance of 2D effects when a large diamagnetic loop is used.This work was made in the framework of project MINOTOR that has received funding from the European Union's Horizon 2020 research and innovation program under Grant agreement No 730028. Additional funding came from the Spanish R&D National Plan (Grant No. PN ESP2016-75887)

Meteors: A Delivery Mechanism of Organic Matter to the Early Earth

All potential exogenous pre-biotic matter arrived to Earth by ways of our atmosphere, where much material was ablated during a luminous phase called "meteors" in rarefied flows of high (up to 270) Mach number. The recent Leonid showers offered a first glimpse into the clusive physical conditions of the ablation process and atmospheric chemistry associated with high-speed meteors. Molecular emissions were detected that trace a meteor's brilliant light to a 4,300 K warm wake rather than to the meteor's head. A new theoretical approach using the direct simulation by Monte Carlo technique identified the source-region and demonstrated that the ablation process is critical in the heating of the meteor's wake. In the head of the meteor, organic carbon appears to survive flash heating and rapid cooling. The temperatures in the wake of the meteor are just right for dissociation of CO and the formation of more complex organic compounds. The resulting materials could account for the bulk of pre-biotic organic carbon on the early Earth at the time of the origin of life.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43257/1/11038_2004_Article_310535.pd

Numerical modeling of repetitive nanosecond discharge in air

International audienceA repetitively pulsed nanosecond glow discharge in a flow of atmospheric pressure air at 2000 K is numerically modelled in the framework of plasma assisted combustion. The plasma is modelled in quasi-neutral approximation with fluid transport and diffusion. In our simulations, 16 species and 115 reactions are considered to model the discharge and the post discharge in air flow, and each phase operates at different time scales. The steady-state regime is reached over 200 cycles from the initial composition at thermodynamic equilibrium. The shape and the electron density of the simulated discharge compare well with experimental measurement

Measurement of ion acceleration in the magnetic nozzle of an ecr plasma thruster

International audienceThe Electron Cyclotron Resonance (ECR) plasma thruster operated with xenon is experimentally studied using laser-induced fluorescence (LIF) spectroscopy. The ion velocity distributions determined from Doppler shift show the axial acceleration of singly charged xenon ions in the magnetic nozzle over several centimeters. LIF results are compared to electrostatic probes measurements

Experimental investigation of magnetic gradient influence in a coaxial ECR plasma thruster

International audienceA technology of electrical propulsion is under development at ONERA: Electron Cyclotron Resonance (ECR) thruster. The principle is based on the resonant heating of electrons in a magnetic field by microwave power, and the ejection of a quasi-neutral plasma in a magnetic nozzle. The plume is electrically neutral, thus no neutralizer is needed, and no power supply other than the microwave supply used to create the plasma is required to accelerate the ions. The influence of the magnetic field on ion current and ion energy distribution is evaluated and the performances with different magnetic field topologies are compared

3D ion velocity distribution function measurement in an electric thruster using laser induced fluorescence tomography

International audienceMeasuring the full ion velocity distribution function (IVDF) by non-intrusive techniques can improve our understanding of the ionization processes and beam dynamics at work in electric thrusters. In this paper, a Laser-Induced Fluorescence (LIF) tomographic reconstruction technique is applied to the measurement of the IVDF in the plume of a miniature Hall effect thruster. A setup is developed to move the laser axis along two rotation axes around the measurement volume. The fluorescence spectra taken from different viewing angles are combined using a tomographic reconstruction algorithm to build the complete 3D (in phase space) time-averaged distribution function. For the first time, this technique is used in the plume of a miniature Hall effect thruster to measure the full distribution function of the xenon ions. Two examples of reconstructions are provided, in front of the thruster nose-cone and in front of the anode channel. The reconstruction reveals the features of the ion beam, in particular on the thruster axis where a toroidal distribution function is observed. These findings are consistent with the thruster shape and operation. This technique, which can be used with other LIF schemes, could be helpful in revealing the details of the ion production regions and the beam dynamics. Using a more powerful laser source, the current implementation of the technique could be improved to reduce the measurement time and also to reconstruct the temporal evolution of the distribution function

Reduced-activation materials for fusion reactors: An overview of the proceedings

Some of the most serious safety and environmental concerns for future fusion reactors involve induced radioactivity in the first wall and blanket structures. One problem caused by the induced radioactivity in a reactor constructed from the conventional austenitic and ferritic steels presently being considered as structural materials would be the disposal of the highly radioactive structures after their service lifetimes. To simplify the waste-disposal process, ''low-activation'' or ''reduced-activation'' alloys are being developed. The objective for such materials is that they qualify for shallow land burial, as opposed to the much more expensive deep geologic disposal. This paper reviews these classes of materials for this purpose: austenitic stainless steels, ferritic steels, and vanadium alloys

Mach 3 shock-wave unsteadiness alleviation using a negative corona discharge

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