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

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

International audienc

Optimization of a coaxial electron cyclotron resonance plasma thruster with an analytical model

International audienceA new cathodeless plasma thruster currently under development at Onera is presented and characterized experimentally and analytically. The coaxial thruster consists of a microwave antenna immersed in a magnetic field, which allows electron heating via cyclotron resonance. The magnetic field diverges at the thruster exit and forms a nozzle that accelerates the quasi-neutral plasma to generate a thrust. Different thruster configurations are tested, and in particular, the influence of the source diameter on the thruster performance is investigated. At microwave powers of about 30W and a xenon flow rate of 0.1mg/s (1 SCCM), a mass utilization of 60% and a thrust of 1mN are estimated based on angular electrostatic probe measurements performed downstream of the thruster in the exhaust plume. Results are found to be in fair agreement with a recent analytical helicon thruster model that has been adapted for the coaxial geometry used here

A TEM study of amorphization in NiTi irradiated with Ni/sup 2 +/ ions at room temperature

Irradiation of a crystalline solid solution can cause the decomposition of the matrix into enhanced, modified thermal, or irradiation-induced precipitate phases. Irradiation can also transform the matrix into a new crystalline phase. Alternatively, the heavily irradiated matrix can become amorphous. Alloys of NiTi are intermetallic compounds with shape-memory applications whose amorphization is of both technological and basic scientific interest. Purpose of this paper is to observe some details of the intermediate stages of amorphization to provide further insight into the mechanisms of the phenomenon

Particle in cell modelling of the observed modes of a dc wire discharge

International audienceLow pressure DC Wire Induced Plasma Sources (WIPS) exhibit two stable modes of discharge- constricted below a threshold pressure and diffuse above. Starting from experimental measurements, we conduct two dimensional particle in cell (PIC) modelling of a DC low pressure (10 −4 − 10 −2 mbar), low current (∼ 1 mA) wire discharge in Helium. 2D PIC modelling is required to capture longitudinal non uniformity of the diffuse mode. PIC simulations reproduce the two discharge modes. Voltage versus pressure curve obtained from simulations matches fairly well experimental data, including the transition region. Discharge voltage dependence on pressure is analysed in consideration of electron impact ionization rates evolution with energy. In light of the PIC findings, a model of the discharge mode transition based on a Child Langmuir theory for ions is proposed. Confrontation with simulated data shows good agreement and validate the model for mode transition prediction. Simulations show that the diffuse mode is a space charge dominated regime

Epitaxial growth of Ni(Al)Si0.7Ge0.3 on Si0.7Ge0.3/Si(100) by Al interlayer mediated epitaxy

Epitaxial growth of Ni(Al)Si0.7Ge0.3 on relaxed Si0.7Ge0.3/Si(100) substrates was achieved via an Al interlayer mediated epitaxy. After annealing, most of the Al atoms from the original 3 nm interlayer diffused toward the surface but the remaining Al atoms in the epitaxial monogermanosilicide distributed uniformly, independent of the annealing temperatures. The incorporation of Al increases the transition temperature from the Ni-rich germanosilicide phase to the monogermanosilicide phase. The reduced Ni diffusion, the increased lattice constant due to substitutional Al, and the increased thermal expansion of monogermanosilicide are assumed to be the main mechanisms enabling the epitaxial growth of the quaternary silicide. (C) 2011 American Institute of Physics. [doi:10.1063/1.3601464