Vénus (planète) | EPFL Graph Search

Vénus est la deuxième planète du Système solaire par ordre d'éloignement au Soleil, et la sixième plus grosse aussi bien par la masse que le diamètre. Elle doit son nom à la déesse romaine de l'amour. Vénus orbite autour du Soleil tous les terrestres. Avec une période de rotation de terrestres, il lui faut plus de temps pour tourner autour de son axe que toute autre planète du Système solaire. Comme Uranus, elle possède une rotation rétrograde et tourne dans le sens opposé à celui des autres planètes : le soleil s'y lève à l'ouest et se couche à l'est. Vénus possède l'orbite la plus circulaire des planètes du Système solaire avec une excentricité orbitale presque nulle et, du fait de sa lente rotation, est quasiment sphérique (aplatissement considéré comme nul). Elle ne possède pas de satellite naturel. Vénus est l'une des quatre planètes telluriques du Système solaire. Elle est parfois appelée la de la Terre en raison des similitudes relatives de leurs diamètres, masses, proximit

Comparison of measured and simulated fast ion velocity distributions in the TEXTOR tokamak

Mattia Albergante, Otto Asunta

Here we demonstrate a comprehensive comparison of collective Thomson scattering (CTS) measurements with steady-state Monte Carlo simulations performed with the ASCOT and VENUS codes. The measurements were taken at a location on the magnetic axis as well as at an off-axis location, using two projection directions at each location. The simulations agree with the measurements on-axis, but for the off-axis geometries discrepancies are observed for both projection directions. For the near perpendicular projection direction with respect to the magnetic field, the discrepancies between measurement and simulations can be explained by uncertainty in plasma parameters. However, the discrepancies between measurement and simulations for the more parallel projection direction cannot be explained solely by uncertainties in plasma parameters. Here anomalous fast ion transport is a possible explanation for the discrepancy.

2011

Interaction Between Fast Ions and Microturbulence in Thermonuclear Devices

Mattia Albergante

The work carried out in this thesis focuses on the interaction between fast ions and turbulence. The aim of the project is to explore this phenomenon and develop the numerical framework required for investigations on present day machines and predictions for burning plasmas. The analysis of the background plasma turbulence and the resulting fast ion diffusivities is carried out with the gyrokinetic code GENE. A set of kinetic transport quantities are defined in order to discriminate the transport of ions with different energies. Gyroaveraging effects are studied. It is observed that only at large values of the E/Te ratio is the particle transport efficiently suppressed (E is the energy of a fast particle and Te the electron temperature). For smaller values, E/Te < 15, larger fast ion transport is observed due to resonant interactions between the particle motion and the phase velocity of the underlying turbulent waves. The transport of fusion generated alpha particles induced by electrostatic fluctuations is lower than collisional expectations, due to their large energies. Magnetic turbulence has an even smaller effect. To verify whether similar conclusions can be drawn for neutral beam ions, substantial upgrades to the VENUS code have been implemented. The results of numerical simulations of the beam ion transport in ITER, DEMO and TCV, with the inclusion of collisional and turbulent effects, are discussed. It is demonstrated that the transport of the 1 MeV ions generated by the neutral beam injector of ITER is only marginally affected by microturbulence and it is concluded that fast ion confinement is not compromised. Given the large plasma temperatures foreseen for DEMO, anomalous transport of beam ions is significant, and in particular collisional models fail to estimate the correct heat deposited on the ions and the electrons. Given the low energy of the planned TCV NBI injector, even stronger anomalies are expected. The effect, however, can be regulated with auxiliary ECRH heating, which would allow for new studies of the fast ion turbulent transport.

EPFL2011

Low-Intensity High-Temperature (LIHT) Solar Cells for Venus Atmosphere

Giulia Tagliabue

Low-intensity high-temperature solar cells that operate effectively in the atmosphere of Venus at various altitudes and also survive on the 465 °C surface of Venus are being developed. Thermal stability, high-temperature current-voltage (I-V), and external quantum efficiency measurements on GaInP/GaAs double-junction solar cells are presented. Solar-cell modeling under the atmospheric conditions of Venus is used to design the optimum solar-cell structure.

2018

Interaction Between Fast Ions and Microturbulence in Thermonuclear Devices

Mattia Albergante

EPFL2011