The Experts below are selected from a list of 52626 Experts worldwide ranked by ideXlab platform
V T Tikhonchuk - One of the best experts on this subject based on the ideXlab platform.
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dense Plasma Heating and shock wave generation by a beam of fast electrons
Physics of Plasmas, 2015Co-Authors: Llor E Aisa, X Ribeyre, S Guskov, Ph Nicolai, V T TikhonchukAbstract:Hot electrons created in laser Plasma interaction at laser intensities 1−10 PW cm−2 in shock ignition scheme can deposit their energy in the shell of the target, augmenting the strength of the ignitor shock. Here, we present a model that describes the effect of the spatial profile of fast electron energy deposition on the dynamics of shock wave formation. A criterion of a strong shock formation is obtained for an arbitrary electron beam distribution function. It is shown that the time and the position of the shock formation are defined by the electron average stopping range, while the strength of the shock decreases as the width of electron energy distribution increases. The latter feature is explained by the fast electron target preheat. The conclusions of theoretical model are confirmed in numerical simulations. The pressure, the strength of the shock, and the efficiency of shock generation are calculated for different electron distributions with the same average stopping range.
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dense Plasma Heating and gbar shock formation by a high intensity flux of energetic electrons
Physics of Plasmas, 2013Co-Authors: X Ribeyre, S Guskov, Ph Nicolai, J L Feugeas, V T TikhonchukAbstract:Process of shock ignition in inertial confinement fusion implies creation of a high pressure shock with a laser spike having intensity of the order of a few PW/cm2. However, the collisional (Bremsstrahlung) absorption at these intensities is inefficient and a significant part of laser energy is converted in a stream of energetic electrons. The process of shock formation in a dense Plasma by an intense electron beam is studied in this paper in a planar geometry. The energy deposition takes place in a fixed mass target layer with the areal density determined by the electron range. A self-similar isothermal rarefaction wave of a fixed mass describes the expanding Plasma. Formation of a shock wave in the target under the pressure of expanding Plasma is described. The efficiency of electron beam energy conversion into the shock wave energy depends on the fast electron energy and the pulse duration. The model is applied to the laser produced fast electrons. The fast electron energy transport could be the domina...
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dense Plasma Heating and gbar shock formation by a high intensity flux of energetic electrons
Physics of Plasmas, 2013Co-Authors: X Ribeyre, S Guskov, Ph Nicolai, J L Feugeas, V T TikhonchukAbstract:Process of shock ignition in inertial confinement fusion implies creation of a high pressure shock with a laser spike having intensity of the order of a few PW/cm2. However, the collisional (Bremsstrahlung) absorption at these intensities is inefficient and a significant part of laser energy is converted in a stream of energetic electrons. The process of shock formation in a dense Plasma by an intense electron beam is studied in this paper in a planar geometry. The energy deposition takes place in a fixed mass target layer with the areal density determined by the electron range. A self-similar isothermal rarefaction wave of a fixed mass describes the expanding Plasma. Formation of a shock wave in the target under the pressure of expanding Plasma is described. The efficiency of electron beam energy conversion into the shock wave energy depends on the fast electron energy and the pulse duration. The model is applied to the laser produced fast electrons. The fast electron energy transport could be the dominant mechanism of ablation pressure creation under the conditions of shock ignition. The shock wave pressure exceeding 1 Gbar during 200–300 ps can be generated with the electron pulse intensity in the range of 5–10 PW/cm2. The conclusions of theoretical model are confirmed in numerical simulations with a radiation hydrodynamic code coupled with a fast electron transport module.
Emmanuel Lanti - One of the best experts on this subject based on the ideXlab platform.
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nonlinear dynamics of energetic particle driven geodesic acoustic modes in asdex upgrade
Physics of Plasmas, 2020Co-Authors: I Novikau, Alessandro Biancalani, E Poli, Ph Lauber, A Bottino, A Di Siena, P Manz, G D Conway, N Ohana, Emmanuel LantiAbstract:Turbulence in tokamaks generates radially sheared zonal flows. Their oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the action of the magnetic field curvature. The GAMs can be driven unstable by an anisotropic energetic particle (EP) population leading to the formation of global radial structures, called energetic-particle-driven geodesic acoustic modes (EGAMs). The EGAMs can redistribute EP energy to the bulk Plasma through collisionless wave-particle interaction. In such a way, the EGAMs might contribute to the Plasma Heating. Thus, investigation of EGAM properties, especially in the velocity space, is necessary for precise understanding of the transport phenomena in tokamak Plasmas. In this work, the nonlinear dynamics of EGAMs without considering the mode interaction with the turbulence is investigated with the help of a Mode-Particle-Resonance (MPR) diagnostic implemented in the global gyrokinetic particle-in-cell code ORB5. An ASDEX Upgrade discharge is chosen as a reference case for this investigation due to its rich EP nonlinear dynamics. An experimentally relevant magnetic field configuration, thermal species profiles, and an EP density profile are taken for EGAM chirping modeling and its comparison with available empirical data. The same magnetic configuration is used to explore energy transfer by the mode from the energetic particles to the thermal Plasma including kinetic electron effects. For a given EGAM level, the Plasma Heating by the mode can be significantly enhanced by varying the EP parameters. Electron dynamics decreases the EGAM saturation amplitude and consequently reduces the Plasma Heating, even though the mode transfers its energy to thermal ions much more than to electrons.
Hui Tian - One of the best experts on this subject based on the ideXlab platform.
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Plasma Heating induced by tadpole like downflows in the flaring solar corona
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: Hui Tian, Bin Chen, Katharine K Reeves, Tanmoy Samanta, Mark C M Cheung, A Vourlidas, Dipankar BanerjeeAbstract:As one of the most spectacular energy release events in the solar system, solar flares are generally powered by magnetic reconnection in the solar corona. As a result of the re-arrangement of magnetic field topology after the reconnection process, a series of new loop-like magnetic structures are often formed and are known as flare loops. A hot diffuse region, consisting of around 5-10 MK Plasma, is also observed above the loops and is called a supra-arcade fan. Often, dark, tadpole-like structures are seen to descend through the bright supra-arcade fans. It remains unclear what role these so-called supra-arcade downflows (SADs) play in Heating the flaring coronal Plasma. Here we show a unique flare observation, where many SADs collide with the flare loops and strongly heat the loops to a temperature of 10-20 MK. Several of these interactions generate clear signatures of quasi-periodic enhancement in the full-Sun-integrated soft X-ray emission, providing an alternative interpretation for quasi-periodic pulsations that are commonly observed during solar and stellar flares.
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possible evidence of alfven cyclotron waves in the angle distribution of magnetic helicity of solar wind turbulence
The Astrophysical Journal, 2011Co-Authors: Eckart Marsch, Shuo Yao, Hui TianAbstract:The fluctuating magnetic helicity is considered an important parameter in diagnosing the characteristic modes of solar wind turbulence. Among them is the Alfv?n-cyclotron wave, which is probably responsible for the solar wind Plasma Heating, but has not yet been identified from the magnetic helicity of solar wind turbulence. Here, we present the possible signatures of Alfv?n-cyclotron waves in the distribution of magnetic helicity as a function of ?VB, which is the angle between the solar wind velocity and local mean magnetic field. We use magnetic field data from the STEREO spacecraft to calculate the ?VB distribution of the normalized reduced fluctuating magnetic helicity ?m. We find a dominant negative ?m for 1 s 150? in the solar wind inward magnetic sector. These features of ?m appearing around the Doppler-shifted ion-cyclotron frequencies may be consistent with the existence of Alfv?n-cyclotron waves among the outward propagating fluctuations. Moreover, right-handed polarized waves at larger propagation angles, which might be kinetic Alfv?n waves or whistler waves, have also been identified on the basis of the ?m features in the angular range 40? < ?VB < 140?. Our findings suggest that Alfv?n-cyclotron waves (together with other wave modes) play a prominent role in turbulence cascading and Plasma Heating of the solar wind.
S Guskov - One of the best experts on this subject based on the ideXlab platform.
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dense Plasma Heating and shock wave generation by a beam of fast electrons
Physics of Plasmas, 2015Co-Authors: Llor E Aisa, X Ribeyre, S Guskov, Ph Nicolai, V T TikhonchukAbstract:Hot electrons created in laser Plasma interaction at laser intensities 1−10 PW cm−2 in shock ignition scheme can deposit their energy in the shell of the target, augmenting the strength of the ignitor shock. Here, we present a model that describes the effect of the spatial profile of fast electron energy deposition on the dynamics of shock wave formation. A criterion of a strong shock formation is obtained for an arbitrary electron beam distribution function. It is shown that the time and the position of the shock formation are defined by the electron average stopping range, while the strength of the shock decreases as the width of electron energy distribution increases. The latter feature is explained by the fast electron target preheat. The conclusions of theoretical model are confirmed in numerical simulations. The pressure, the strength of the shock, and the efficiency of shock generation are calculated for different electron distributions with the same average stopping range.
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dense Plasma Heating and gbar shock formation by a high intensity flux of energetic electrons
Physics of Plasmas, 2013Co-Authors: X Ribeyre, S Guskov, Ph Nicolai, J L Feugeas, V T TikhonchukAbstract:Process of shock ignition in inertial confinement fusion implies creation of a high pressure shock with a laser spike having intensity of the order of a few PW/cm2. However, the collisional (Bremsstrahlung) absorption at these intensities is inefficient and a significant part of laser energy is converted in a stream of energetic electrons. The process of shock formation in a dense Plasma by an intense electron beam is studied in this paper in a planar geometry. The energy deposition takes place in a fixed mass target layer with the areal density determined by the electron range. A self-similar isothermal rarefaction wave of a fixed mass describes the expanding Plasma. Formation of a shock wave in the target under the pressure of expanding Plasma is described. The efficiency of electron beam energy conversion into the shock wave energy depends on the fast electron energy and the pulse duration. The model is applied to the laser produced fast electrons. The fast electron energy transport could be the domina...
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dense Plasma Heating and gbar shock formation by a high intensity flux of energetic electrons
Physics of Plasmas, 2013Co-Authors: X Ribeyre, S Guskov, Ph Nicolai, J L Feugeas, V T TikhonchukAbstract:Process of shock ignition in inertial confinement fusion implies creation of a high pressure shock with a laser spike having intensity of the order of a few PW/cm2. However, the collisional (Bremsstrahlung) absorption at these intensities is inefficient and a significant part of laser energy is converted in a stream of energetic electrons. The process of shock formation in a dense Plasma by an intense electron beam is studied in this paper in a planar geometry. The energy deposition takes place in a fixed mass target layer with the areal density determined by the electron range. A self-similar isothermal rarefaction wave of a fixed mass describes the expanding Plasma. Formation of a shock wave in the target under the pressure of expanding Plasma is described. The efficiency of electron beam energy conversion into the shock wave energy depends on the fast electron energy and the pulse duration. The model is applied to the laser produced fast electrons. The fast electron energy transport could be the dominant mechanism of ablation pressure creation under the conditions of shock ignition. The shock wave pressure exceeding 1 Gbar during 200–300 ps can be generated with the electron pulse intensity in the range of 5–10 PW/cm2. The conclusions of theoretical model are confirmed in numerical simulations with a radiation hydrodynamic code coupled with a fast electron transport module.
Ying Liu - One of the best experts on this subject based on the ideXlab platform.
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Temperature Anisotropy in a Shocked Plasma: Mirror-Mode Instabilities in the Heliosheath
The Astrophysical Journal, 2007Co-Authors: Ying Liu, John D. Richardson, John W. Belcher, Justin C. KasperAbstract:We show that temperature anisotropies induced at a shock can account for interplanetary and planetary bow shock observations. Shocked Plasma with enhanced Plasma β is preferentially unstable to the mirror-mode instability downstream of a quasi-perpendicular shock and to the fire-hose instability downstream of a quasi-parallel shock, consistent with magnetic fluctuations observed downstream of a large variety of shocks. Our theoretical analysis of the solar wind termination shock suggests that the magnetic holes observed by Voyager 1 in the heliosheath are produced by the mirror-mode instability. The results are also of astrophysical interest, providing an energy source for Plasma Heating.
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temperature anisotropy in a shocked Plasma mirror mode instabilities in the heliosheath
arXiv: Astrophysics, 2007Co-Authors: Ying Liu, J D Richardson, J W Belcher, J C KasperAbstract:We show that temperature anisotropies induced at a shock can account for interplanetary and planetary bow shock observations. Shocked Plasma with enhanced Plasma beta is preferentially unstable to the mirror mode instability downstream of a quasi-perpendicular shock and to the firehose instability downstream of a quasi-parallel shock, consistent with magnetic fluctuations observed downstream of a large variety of shocks. Our theoretical analysis of the solar wind termination shock suggests that the magnetic holes observed by Voyager 1 in the heliosheath are produced by the mirror mode instability. The results are also of astrophysical interest, providing an energy source for Plasma Heating.
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thermodynamic structure of collision dominated expanding Plasma Heating of interplanetary coronal mass ejections
Journal of Geophysical Research, 2006Co-Authors: Ying Liu, J D Richardson, J W Belcher, J C Kasper, H A ElliottAbstract:[1] We investigate the thermodynamic structure of interplanetary coronal mass ejections (ICMEs) using combined surveys of the ejecta between 0.3 and 20 AU. ICMEs are shown to have a moderate expansion in the solar wind compared with theoretical predictions. The expansion seems to be governed by a polytrope with γ ∼ 1.3 in this distance range. We find that Coulomb collisions are important contributors to the ion-ion equilibration process in the ICME Plasma. The alpha-proton differential speed quickly drops to below 10 km s−1 due to strong Coulomb collisions. However, the two species of particles are far from thermal equilibrium with a temperature ratio Tα/Tp = 4–6, suggestive of a preferential Heating of alpha particles. The Plasma Heating rate as a function of heliocentric distance required for the temperature profile is deduced by taking into account the expansion and energy transfer between protons and alphas via Coulomb collisions. The turbulence dissipation rate is also inferred from the inertial range power spectrum of magnetic fluctuations within ICMEs. Comparison of the turbulence dissipation rate with the required Heating rate shows that turbulence dissipation seems sufficient to explain the ICME Heating. Sources powering the turbulence are also investigated by examining the instabilities induced by temperature anisotropies and energy deposition by pickup ions.