Search results for "asma"
showing 10 items of 4204 documents
Assessment of Fatigue Effects Induced by Fast Beam Transients in the IFMIF-DONES Li Target
2020
One of the crucial steps toward the commercial exploitation of fusion energy is the availability of a high-intensity neutron source able to test and qualify structural materials to be used in future fusion power reactors. The International Fusion Materials Irradiation Facility-DEMO Oriented NEutron Source (IFMIF-DONES) facility, which is currently being designed within the framework of the EUROfusion Consortium, represents the European effort to develop such a neutron source. It employs a liquid lithium target struck by an accelerated deuteron (D+) beam to produce fusion-like neutrons used to irradiate materials samples. So far, a detailed investigation of the thermomechanical behavior of t…
The Mach cone signal and energy deposition scenarios in linearized hydrodynamics
2010
Particle correlation measurements associated with a hard or semi-hard trigger in heavy-ion collisions may reflect Mach cone shockwaves excited in the bulk medium by partonic energy loss. This is of great interest because, when compared with theory, such measurements can provide information on the transport properties of the medium. Specifically, the formation of Mach cone shockwaves is sensitive to the viscosity and speed of sound, as well as the detailed nature of the jet medium interaction. However, modeling the physics of shockwave excitation to obtain a meaningful comparison with the measured correlations is very challenging since the correlations arise from an interplay of perturbative…
Accretion shock on CTTSs and its X-ray emission
2009
High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at T~2-3×10^6 K and ne~10^11-10^13 cm-3. Stationary models suggest that this emission is due to shock-heated accreting material. We address this issue by a 1-D hydrodynamic model of the impact of the accretion flow onto a chromosphere of a CTTS with the aim of investigating the stability of accretion shock and the role of the chromosphere. Our simulations include the effects of gravity, radiative losses from optically thin plasma, the thermal conduction and a detailed modeling of the stellar chromosphere. Here we present the results of a simulation based on the parameters of the…
Incoherent dispersive shocks in the spectral evolution of random waves
2013
We predict theoretically and numerically the existence of incoherent dispersive shock waves. They manifest themselves as an unstable singular behavior of the spectrum of incoherent waves that evolve in a noninstantaneous nonlinear environment. This phenomenon of "spectral wave breaking" develops in the weakly nonlinear regime of the random wave. We elaborate a general theoretical formulation of these incoherent objects on the basis of a weakly nonlinear statistical approach: a family of singular integro-differential kinetic equations is derived, which provides a detailed deterministic description of the incoherent dispersive shock wave phenomenon.
Shock-induced complex phase-space dynamics of strongly turbulent flows
2017
Shock waves have been thoroughly investigated during the last century in many different branches of physics. In conservative (Hamiltonian) systems the shock singularity is regularized by weak wave dispersion, thus leading to the formation of a rapidly and regular oscillating structure, usually termed in the literature dispersive shock wave (DSW), see e.g. [1]. Here, we show that this fundamental singular process of DSW formation can break down in a system of incoherent nonlinear waves. We consider the strong turbulent regime of a system of nonlocal nonlinear optical waves. We report theoretically and experimentally a characteristic transition: Strengthening the nonlocal character of the non…
High order accurate shock capturing schemes for two-component Richtmyer-Meshkov instabilities in compressible magnetohydrodynamics
2011
We design a conservative and entropy satisfying numerical scheme to perform numerical simulations of two component Richtmyer-Meshkov (RM) instabilities in compressible magnetohydrodynamics (MHD). We first formulate a conservative model of a two-component compressible MHD fluid ruled under two ideal gases with different adiabatic exponents. The formulation includes a level set function that allows to evolve the two components of the plasma in a conservative and consistent way. We present a set of examples including two-component Riemann problems and high Mach shock wave interactions with entropy contact waves that validate the high order accurate numerical scheme. We observe that turbulent r…
Laboratory evidence for proton energization by collisionless shock surfing
2021
Charged particles can be accelerated to high energies by collisionless shock waves in astrophysical environments, such as supernova remnants. By interacting with the magnetized ambient medium, these shocks can transfer energy to particles. Despite increasing efforts in the characterization of these shocks from satellite measurements at Earth’s bow shock as well as powerful numerical simulations, the underlying acceleration mechanism or a combination thereof is still widely debated. Here we show that astrophysically relevant super-critical quasi-perpendicular magnetized collisionless shocks can be produced and characterized in the laboratory. We observe the characteristics of super-criticali…
Hydrodynamic Modeling of Accretion Impacts in Classical T Tauri Stars: Radiative Heating of the Pre-shock Plasma
2016
Context. It is generally accepted that, in classical T Tauri stars, the plasma from the circumstellar disc accretes onto the stellar surface with free-fall velocity and the impact generates a shock. The impact region is expected to contribute to emission in different spectral bands; many studies have confirmed that the X-rays arise from the post-shock plasma but, otherwise, there are no studies in the literature investigating the origin of the observed UV emission which is apparently correlated to accretion. Aims: We investigated the effect of radiative heating of the infalling material by the post-shock plasma at the base of the accretion stream, with the aim to identify in which region a …
Metastable oxygen atom velocity and temperature in supersonic CO2plasma expansions
2008
Radial and axial velocity distribution functions of metastable oxygen atoms were obtained by way of resonant laser induced fluorescence spectroscopy at 777.19 nm in rarefied supersonic plasma jets produced from pure CO2 and CO2–N2 gas mixtures. The N2 seeded fraction is 3% in volume in order to mimic the Martian atmosphere composition. The measured lineshapes allow computation of the mean radial velocity and the perpendicular temperature, with respect to the jet axis, as well as the mean axial velocity and the parallel temperature. With an arcjet plasma source input power of 6.5 kW, the metastable O(5S) atom axial velocity is around 4500 m s−1 and the atom perpendicular temperature reaches …
Spectral long-range interaction of temporal incoherent solitons.
2014
We study the interaction of temporal incoherent solitons sustained by a highly noninstantaneous (Raman-like) nonlinear response. The incoherent solitons exhibit a nonmutual interaction, which can be either attractive or repulsive depending on their relative initial distance. The analysis reveals that incoherent solitons exhibit a long-range interaction in frequency space, which is in contrast with the expected spectral short-range interaction described by the usual approach based on the Raman-like spectral gain curve. Both phenomena of anomalous interaction and spectral long-range behavior of incoherent solitons are described in detail by a long-range Vlasov equation.