P. Savoini - Academia.edu (original) (raw)
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Journal of Geophysical Research Atmospheres
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Recent statistical analysis of results issued from test particles simulations has been performed ... more Recent statistical analysis of results issued from test particles simulations has been performed in order to analyze quantitatively the adiabaticity violation for electrons traversing a planar quasi-perpendicular shock wave The shock wave is moving in a supercritical regime and its profile is defined by all electric and magnetic field components issued from a full particle simulation. Test particles are initially distributed over a small sphere in 3D velocity space. The main results are: (i) both adiabatic and nonadiabatic electrons are identified and their respective contributions to the total heating are also estimated versus their initial distributions in velocity phases (for a given thermal velocity) and versus the initial thermal velocity. This allows us to determine which part of the distribution function is responsible for nonadiabaticity. (ii) Two distinct nonadiabatic electron populations have been clearly identified: one is super-adiabatic (overheating), the other is sub-adiabatic (overcooling). Results are compared with recent theoretical calculations suggested to explain the existence of these two populations and to identify the underlying mechanisms responsible for their formation. Present results may be of importance for analysing new experimental data issued from CLUSTER-II mission.
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Mechanisms responsible for electron adiabaticity breakdown have been recently analyzed by theory ... more Mechanisms responsible for electron adiabaticity breakdown have been recently analyzed by theory and test particles technics based on a given set of E and B fields profiles i.e. where the shock front is supposed to be stationary (Savoini and al., 2003, 2004). One striking features is that 2 classes of nonadiabatic electrons ("overadiabatic" and "underadiabatic") have been evidenced. However, both experimental measurements and previous simulations have evidenced that the shock front is nonstationary even at moderate supercritical Mach numbers. One invoked source of nonstationarity is the so-called self reformation of the shock front which has been analyzed with full PIC simulations. The cyclic time of this reformation is of the order of the ion gyroperiod estimated from the averaged B field (i.e. lower than the upstream gyroperiod). For relatively high mass ratio, the scale of shock front is strongly varying within this cycle with time ranges where the ramp and the foot are alternatively well separated (steepy ramp) or mixed (smooth ramp). This present analysis is based on test particles (in the full 3D velocity space) interacting with time varying fields of the shock front issued from full particle simulations for a strictly perpendicular shock. Present results stress that the self-reformation affects (i) the relative percentage of adiab/nonadiab electrons, (ii) the features of "over" and under" adiabatic electrons.
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ABSTRACT
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ABSTRACT
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Test particle simulations are performed in order to analyze in details the dynamics of transmitte... more Test particle simulations are performed in order to analyze in details the dynamics of transmitted electrons through a supercritical strictly perpendicular stationary collisionless shock Recent analysis Savoini et al Ann Geophy 2005 has evidenced three electron populations i adiabatic ii over-adiabatic characterized by an increase of the gyrating velocity higher than that expected from the conservation of the magnetic moment and iii under-adiabatic characterized by a decrease of this velocity and not predicted by any existing theory Criteria specific to each population have been clearly identified Presently this work is extended by investigating the impact on the intrinsic nonstationarity of a 2-D shock front revealed by the self-reformation along the shock normal and the shock front rippling Analysis of individual time particle trajectories is performed and completed by statistics based on different upstream distributions spherical shell and Maxwellian All combined nonstationary and nonuniformity effects have a filtering impact leading to a main and compensative variation in the relative percentages of adiabatic and emph over-adiabatic populations in contrast with under-adiabatic population which is relatively poorly affected
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ABSTRACT
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ABSTRACT
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ABSTRACT
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Journal of Geophysical Research Atmospheres
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Recent statistical analysis of results issued from test particles simulations has been performed ... more Recent statistical analysis of results issued from test particles simulations has been performed in order to analyze quantitatively the adiabaticity violation for electrons traversing a planar quasi-perpendicular shock wave The shock wave is moving in a supercritical regime and its profile is defined by all electric and magnetic field components issued from a full particle simulation. Test particles are initially distributed over a small sphere in 3D velocity space. The main results are: (i) both adiabatic and nonadiabatic electrons are identified and their respective contributions to the total heating are also estimated versus their initial distributions in velocity phases (for a given thermal velocity) and versus the initial thermal velocity. This allows us to determine which part of the distribution function is responsible for nonadiabaticity. (ii) Two distinct nonadiabatic electron populations have been clearly identified: one is super-adiabatic (overheating), the other is sub-adiabatic (overcooling). Results are compared with recent theoretical calculations suggested to explain the existence of these two populations and to identify the underlying mechanisms responsible for their formation. Present results may be of importance for analysing new experimental data issued from CLUSTER-II mission.
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Mechanisms responsible for electron adiabaticity breakdown have been recently analyzed by theory ... more Mechanisms responsible for electron adiabaticity breakdown have been recently analyzed by theory and test particles technics based on a given set of E and B fields profiles i.e. where the shock front is supposed to be stationary (Savoini and al., 2003, 2004). One striking features is that 2 classes of nonadiabatic electrons ("overadiabatic" and "underadiabatic") have been evidenced. However, both experimental measurements and previous simulations have evidenced that the shock front is nonstationary even at moderate supercritical Mach numbers. One invoked source of nonstationarity is the so-called self reformation of the shock front which has been analyzed with full PIC simulations. The cyclic time of this reformation is of the order of the ion gyroperiod estimated from the averaged B field (i.e. lower than the upstream gyroperiod). For relatively high mass ratio, the scale of shock front is strongly varying within this cycle with time ranges where the ramp and the foot are alternatively well separated (steepy ramp) or mixed (smooth ramp). This present analysis is based on test particles (in the full 3D velocity space) interacting with time varying fields of the shock front issued from full particle simulations for a strictly perpendicular shock. Present results stress that the self-reformation affects (i) the relative percentage of adiab/nonadiab electrons, (ii) the features of "over" and under" adiabatic electrons.
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ABSTRACT
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ABSTRACT
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Test particle simulations are performed in order to analyze in details the dynamics of transmitte... more Test particle simulations are performed in order to analyze in details the dynamics of transmitted electrons through a supercritical strictly perpendicular stationary collisionless shock Recent analysis Savoini et al Ann Geophy 2005 has evidenced three electron populations i adiabatic ii over-adiabatic characterized by an increase of the gyrating velocity higher than that expected from the conservation of the magnetic moment and iii under-adiabatic characterized by a decrease of this velocity and not predicted by any existing theory Criteria specific to each population have been clearly identified Presently this work is extended by investigating the impact on the intrinsic nonstationarity of a 2-D shock front revealed by the self-reformation along the shock normal and the shock front rippling Analysis of individual time particle trajectories is performed and completed by statistics based on different upstream distributions spherical shell and Maxwellian All combined nonstationary and nonuniformity effects have a filtering impact leading to a main and compensative variation in the relative percentages of adiabatic and emph over-adiabatic populations in contrast with under-adiabatic population which is relatively poorly affected
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ABSTRACT
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