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Devendra Sharma - One of the best experts on this subject based on the ideXlab platform.
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Ultra slow electron holes in Collisionless Plasmas: stability at high ion temperature
Physics of Plasmas, 2020Co-Authors: Debraj Mandal, Devendra Sharma, Hans SchamelAbstract:Numerical simulations recover ultra slow solitary electron holes (SEH) of electron-acoustic genre propagating stably well below the ion acoustic speed Cs where no pure electron perturbation is known to exist yet, as they are disallowed by the ion response. Recovered at high ion temperature (Ti > Te), the reason of this stability (unaccelerated propagation, unseen before in existing literature) of SEH is traced to the loss of neutralizing cold ion response. In the opposite case of a background of sufficiently cold ions, Te > 3.5Ti, SEHs are accompanied by an ion compression that yields phase velocities above Cs (ion acoustic genre) and accelerates them, forcing a jump over a forbidden velocity gap, and settle on the high velocity tail of the electron distribution fe. In the observed ultra slow structures having Ti > Te, however, the warm ions begin to supplement the electron response and show Boltzmann-like behavior, transforming the ion compression to decompression (rarefaction) at the hole location. SEHs hence belong to the continuous spectrum of slow electron acoustic-like modes being triggered by the electron trapping nonlinearity. The results also suggest a scope of generalization of the basic EH theory.
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on the nonlinear trapping nature of undamped coherent structures in Collisionless Plasmas and its impact on stability
Physics of Plasmas, 2017Co-Authors: H Schamel, Debraj Mandal, Devendra SharmaAbstract:An outstanding notion for Collisionless Plasmas is the essential nonlinear character of their coherent structures, which in the stationary, weak amplitude limit are described by a continuum of cnoidal electron and ion hole modes governed by a multiparametric nonlinear dispersion relation. The well-known discrete structure of undamped linear plasma modes is seamlessly embedded in this nonlinear continuum as the microscopic texture of plasma begins to reveal itself in the high temperature Collisionless plasma limit. This transforms the linear-threshold-based operating mechanism of plasma turbulence into a fundamental nonlinear, multifaceted one. Based on a comprehensive three-level description of increasing profundity, a proof of this novel dictum is presented, which makes use of the joint properties of such structures, their coherency and stationarity, and uses in succession a fluid, linear Vlasov and a full Vlasov description. It unifies discrete and continuum limits by resolving the inevitable resonant r...
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Nonlinearly interacting trapped particle solitons in Collisionless Plasmas
Physics of Plasmas, 2016Co-Authors: Debraj Mandal, Devendra SharmaAbstract:The formulation of collective waves in Collisionless Plasmas is complicated by the kinetic effects produced by the resonant particles, capable of responding to the smallest of the amplitude disturbance. The dispersive plasma manifests this response by generating coherentnonlinear structures associated with phase-space vortices, or holes, at very small amplitudes. The nonlinear interaction between solitary electron phase-space holes is studied in the electron acoustic regime of a Collisionless plasma using Vlasov simulations. Evolution of the analytic trapped particle solitary solutions is examined, observing them propagate stably, preserve their identity across strong mutual interactions in adiabatic processes, and display close correspondence with observable processes in nature.
Debraj Mandal - One of the best experts on this subject based on the ideXlab platform.
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Ultra slow electron holes in Collisionless Plasmas: stability at high ion temperature
Physics of Plasmas, 2020Co-Authors: Debraj Mandal, Devendra Sharma, Hans SchamelAbstract:Numerical simulations recover ultra slow solitary electron holes (SEH) of electron-acoustic genre propagating stably well below the ion acoustic speed Cs where no pure electron perturbation is known to exist yet, as they are disallowed by the ion response. Recovered at high ion temperature (Ti > Te), the reason of this stability (unaccelerated propagation, unseen before in existing literature) of SEH is traced to the loss of neutralizing cold ion response. In the opposite case of a background of sufficiently cold ions, Te > 3.5Ti, SEHs are accompanied by an ion compression that yields phase velocities above Cs (ion acoustic genre) and accelerates them, forcing a jump over a forbidden velocity gap, and settle on the high velocity tail of the electron distribution fe. In the observed ultra slow structures having Ti > Te, however, the warm ions begin to supplement the electron response and show Boltzmann-like behavior, transforming the ion compression to decompression (rarefaction) at the hole location. SEHs hence belong to the continuous spectrum of slow electron acoustic-like modes being triggered by the electron trapping nonlinearity. The results also suggest a scope of generalization of the basic EH theory.
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on the nonlinear trapping nature of undamped coherent structures in Collisionless Plasmas and its impact on stability
Physics of Plasmas, 2017Co-Authors: H Schamel, Debraj Mandal, Devendra SharmaAbstract:An outstanding notion for Collisionless Plasmas is the essential nonlinear character of their coherent structures, which in the stationary, weak amplitude limit are described by a continuum of cnoidal electron and ion hole modes governed by a multiparametric nonlinear dispersion relation. The well-known discrete structure of undamped linear plasma modes is seamlessly embedded in this nonlinear continuum as the microscopic texture of plasma begins to reveal itself in the high temperature Collisionless plasma limit. This transforms the linear-threshold-based operating mechanism of plasma turbulence into a fundamental nonlinear, multifaceted one. Based on a comprehensive three-level description of increasing profundity, a proof of this novel dictum is presented, which makes use of the joint properties of such structures, their coherency and stationarity, and uses in succession a fluid, linear Vlasov and a full Vlasov description. It unifies discrete and continuum limits by resolving the inevitable resonant r...
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Nonlinearly interacting trapped particle solitons in Collisionless Plasmas
Physics of Plasmas, 2016Co-Authors: Debraj Mandal, Devendra SharmaAbstract:The formulation of collective waves in Collisionless Plasmas is complicated by the kinetic effects produced by the resonant particles, capable of responding to the smallest of the amplitude disturbance. The dispersive plasma manifests this response by generating coherentnonlinear structures associated with phase-space vortices, or holes, at very small amplitudes. The nonlinear interaction between solitary electron phase-space holes is studied in the electron acoustic regime of a Collisionless plasma using Vlasov simulations. Evolution of the analytic trapped particle solitary solutions is examined, observing them propagate stably, preserve their identity across strong mutual interactions in adiabatic processes, and display close correspondence with observable processes in nature.
Grzegorz Kowal - One of the best experts on this subject based on the ideXlab platform.
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turbulence in Collisionless Plasmas statistical analysis from numerical simulations with pressure anisotropy
New Journal of Physics, 2011Co-Authors: Grzegorz Kowal, D Falcetagoncalves, A LazarianAbstract:In recent years, we have experienced increasing interest in the understanding of the physical properties of Collisionless Plasmas, mostly because of the large number of astrophysical environments (e.g. the intracluster medium (ICM)) containing magnetic fields that are strong enough to be coupled with the ionized gas and characterized by densities sufficiently low to prevent the pressure isotropization with respect to the magnetic line direction. Under these conditions, a new class of kinetic instabilities arises, such as firehose and mirror instabilities, which have been studied extensively in the literature. Their role in the turbulence evolution and cascade process in the presence of pressure anisotropy, however, is still unclear. In this work, we present the first statistical analysis of turbulence in Collisionless Plasmas using three-dimensional numerical simulations and solving double-isothermal magnetohydrodynamic equations with the Chew-Goldberger-Low laws closure (CGL-MHD). We study models with different initial conditions to account for the firehose and mirror instabilities and to obtain different turbulent regimes. We found that the CGL- MHD subsonic and supersonic turbulences show small differences compared
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turbulence in Collisionless Plasmas statistical analysis from numerical simulations with pressure anisotropy
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Grzegorz Kowal, D Falcetagoncalves, A LazarianAbstract:In the past years we have experienced an increasing interest in understanding of the physical properties of Collisionless Plasmas, mostly because of the large number of astrophysical environments, e.g. the intracluster medium (ICM), containing magnetic fields which are strong enough to be coupled with the ionized gas and characterized by densities sufficiently low to prevent the pressure isotropization with respect to the magnetic line direction. Under these conditions a new class of kinetic instabilities arises, such as firehose and mirror ones, which were extensively studied in the literature. Their role in the turbulence evolution and cascade process in the presence of pressure anisotropy, however, is still unclear. In this work we present the first statistical analysis of turbulence in Collisionless Plasmas using three dimensional double isothermal magnetohydrodynamical with the Chew-Goldberger-Low closure (CGL-MHD) numerical simulations. We study models with different initial conditions to account for the firehose and mirror instabilities and to obtain different turbulent regimes. We study the probability distribution functions, spectra, structure functions and anisotropy of density and velocity fluctuations. The results indicate that in some cases the instabilities significantly modifies the statistical properties of turbulence and even though preliminary and restricted to very specific conditions, show that the physical properties of turbulence in Collisionless Plasmas, as those found in the ICM, may be very different from what has been largely believed. Implications can range from interchange of energies to cosmic rays acceleration.
Yosuke Matsumoto - One of the best experts on this subject based on the ideXlab platform.
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turbulent mixing and transport of Collisionless Plasmas across a stratified velocity shear layer
Journal of Geophysical Research, 2006Co-Authors: Yosuke Matsumoto, Masahiro HoshinoAbstract:[1] Two-dimensional simulations of the Kelvin-Helmholtz (K-H) instability in a nonuniform density medium and with the transverse magnetic field show the strong development of turbulence through nonlinear instabilities. Ideal MHD simulation results have indicated that the difference in density between two media plays a crucial role on the fast turbulent mixing and transport. The onset of the turbulence is triggered not only by the secondary K-H instability but also by the Rayleigh-Taylor (R-T) instability at the density interface inside the normal K-H vortex. The secondary R-T instability alters macroscopic structure by transporting dense fluids to tenuous region, while the secondary K-H instability is just a seed for the turbulence. Full particle simulations are also conducted and reproduces the similar result of the ideal MHDs, except that the strong electrostatic field caused by the secondary R-T instability scatters ions and deforms the electron density interface. As a result, the mixing area increases anomalously fast and extends spatially as compared to the result in the uniform density case.
Z Lin - One of the best experts on this subject based on the ideXlab platform.
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nonlinear frequency oscillation of alfven eigenmodes in fusion Plasmas
Physical Review Letters, 2012Co-Authors: H S Zhang, Z Lin, I HolodAbstract:A nonlinear oscillation of frequency and amplitude is found by massively parallel gyrokinetic simulations of Alfv\'en eigenmodes excited by energetic particles in toroidal Plasmas. The fast and repetitive frequency chirping is induced by the evolution of coherent structures in the phase space. The dynamics of the coherent structures is controlled by the competition between the phase-space island formation due to the nonlinear particle trapping and the island destruction due to the free streaming. The chirping dynamics provides a conceptual framework for understanding nonlinear wave-particle interactions underlying the transport process in Collisionless Plasmas.
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turbulent transport of trapped electron modes in Collisionless Plasmas
Physical Review Letters, 2009Co-Authors: Yong Xiao, Z LinAbstract:Global gyrokinetic particle simulations of Collisionless trapped-electron mode turbulence in toroidal Plasmas find that electron heat transport exhibits a device size scaling with a gradual transition from Bohm to gyro-Bohm scaling. A comprehensive analysis of spatial and temporal scales shows that the turbulence eddies are predominantly microscopic because of zonal flow shearing, but the presence of mesoscale structures drives a nondiffusive component in the electron heat flux due to the weak nonlinear detuning of the precessional resonance that excites the linear instability.
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wave particle decorrelation and transport of anisotropic turbulence in Collisionless Plasmas
Physical Review Letters, 2007Co-Authors: Z Lin, P. H. Diamond, I Holod, Liu Chen, T S Hahm, Stephane EthierAbstract:Comprehensive analysis of the largest first-principles simulations to date shows that stochastic wave-particle decorrelation is the dominant mechanism responsible for electron heat transport driven by electron temperature gradient turbulence with extended radial streamers. The transport is proportional to the local fluctuation intensity, and phase-space island overlap leads to a diffusive process with a time scale comparable to the wave-particle decorrelation time, determined by the fluctuation spectral width. This kinetic time scale is much shorter than the fluid time scale of eddy mixing.