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تسجيل مستخدم جديدNonlinear Landau resonant interaction between kinetic Alfven waves and thermal electrons: Excitation of time domain structures
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Phase space holes, double layers and other solitary electric field structures, referred to as time domain structures (TDSs), often occur around dipolarization fronts in the Earths inner magnetosphere. They are considered to be important because of their role in the dissipation of the injection energy and their potential for significant particle scattering and acceleration. Kinetic Alfven waves are observed to be excited during energetic particle injections, and are typically present in conjunction with TDS observations. Despite the availability of a large number of spacecraft observations, the origin of TDSs and their relation to kinetic Alfven waves remains poorly understood to date. Part of the difficulty arises from the vast scale separations between kinetic Alfven waves and TDSs. Here, we demonstrate that TDSs can be excited by electrons in nonlinear Landau resonance with kinetic Alfven waves. These electrons get trapped by the parallel electric field of kinetic Alfven waves, form localized beam distributions, and subsequently generate TDSs through beam instabilities. A big picture emerges as follows: macroscale dipolarization fronts first transfer the ion flow (kinetic) energy to kinetic Alfven waves at intermediate scale, which further channel the energy to TDSs at the microscale and eventually deposit the energy to the thermal electrons in the form of heating. In this way, the ion flow energy associated with dipolarization fronts is effectively dissipated in a cascade from large to small scales in the inner magnetosphere.
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Turbulence is thought to play a role in the heating of the solar wind plasma, though many questions remain to be solved regarding the exact nature of the mechanisms driving this process in the heliosphere. In particular, the physics of the collisionl
ess interactions between particles and turbulent electromagnetic fields in the kinetic dissipation range of the turbulent cascade remains incompletely understood. A recent analysis of an interval of Magnetosphere Multiscale (MMS) observations has used the field-particle correlation technique to demonstrate that electron Landau damping is involved in the dissipation of turbulence in the Earths magnetosheath. Motivated by this discovery, we perform a high-resolution gyrokinetic numerical simulation of the turbulence in the MMS interval to investigate the role of electron Landau damping in the dissipation of turbulent energy. We employ the field-particle correlation technique on our simulation data, compare our results to the known velocity-space signatures of Landau damping outside the dissipation range, and evaluate the net electron energization. We find qualitative agreement between the numerical and observational results for some key aspects of the energization and speculate on the nature of disagreements in light of experimental factors, such as differences in resolution, and of developing insights into the nature of field-particle interactions in the presence of dispersive kinetic Alfven waves.
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