P. Savoini - Profile on Academia.edu (original) (raw)
Papers by P. Savoini
Simulations de la dynamique des electrons a travers une onde de choc non- collisionnelle
Adiabaticity breakdown for electron Maxwellian distribution
Breakdown of Adiabaticity For Electrons Transmitted Through A Quasiperpendicular Shock: Part 1- Basic Mechanisms
ABSTRACT
Nonadiabatic Electron Heating and Cooling Through A Self-consistent Quasi-perpendicular Shock. Part 2: A Statistical Analysis
ABSTRACT
Erratum: ``Electron dynamics in two- and one-dimensional oblique supercritical collisionless magnetosonic shocks'' [Journal of Geophysical Research, 99, 6609-6639 (1994)]
Journal of Geophysical Research Atmospheres
Super-Adiabatic and Sub-Adiabatic Electron Heating Through a Quasiperpendicular Supercritical Shock
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.
Impact of the shock front nonstationarity on the formation of adiabatic/nonadiabatic electrons
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.
Adiabaticity breakdown for electrons crossing the stationary/nonstationary front of a collisionless perpendicular shock in supercritical regime
The electron physics of collisionless shocks
Microsintability within the foot of perpendicular supercritical shock: recent PIC simulations
Over and under nonadiabatic electron heating through a perpendicular shock: a statistical approach
Nonstationarity of perpendicular shocks
Nonstationarity of Perpendicular Shock Front: Hybrid Versus PIC Simulations
Dynamics of electrons reflected at collisionless shocks: impact of the shock front turbulence
Reformation of Perpendicular Shocks: 1-D VS 2-D Simulations
ABSTRACT
Breakdown of adiabaticity for electron Maxwellian distribution through a stationary/nonstationary perpendicular supercritical shock
ABSTRACT
Breakdown of electrons adiabaticity: role of nonstationarities in a perpendicular supercritical shock
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
Nonstationarity of two-dimensional supercrititical perpendicular shocks: evidence of competing mechanims
ABSTRACT
1] The shock front nonstationarity of perpendicular shocks in super-critical regime is analyzed b... more 1] The shock front nonstationarity of perpendicular shocks in super-critical regime is analyzed by examining the coupling between ''incoming'' and ''reflected'' ion populations. For a given set of parameters including the upstream Mach number (M A ) and the fraction a of reflected to incoming ions, a self-consistent, time-stationary solution of the coupling between ion streams and the electromagnetic field is sought for. If such a solution is found, the shock is stationary; otherwise, the shock is nonstationary, leading to a self-reforming shock front often observed in full particle simulations of quasiperpendicular shocks. A parametric study of this numerical model allows us to define a critical a crit between stationary and nonstationary regimes. The shock can be nonstationary even for relatively low M A (2-5). For a moderate M A (5-10), the critical value a crit is about 15 to 20%. For very high M A (>10), a crit saturates around 20%. Moreover, present full simulations show that self-reformation of the shock front occurs for relatively low b i and disappears for high b i , where b i is the ratio of upstream ion plasma to magnetic field pressures. Results issued from the present theoretical model are found to be in good agreement with full particle simulations for low b i case; this agreement holds as long as the motion of reflected ions is coherent enough (narrow ion ring) to be described by a single population in the model. The present model reveals to be ''at variance'' with full particle simulations results for the high b i case. Present results are also compared with previous hybrid simulations.
Adiabatic and nonadiabatic electrons through the stationary/ nonstationary front of a collisionless perpendicular shock in supercritical regime
Simulations de la dynamique des electrons a travers une onde de choc non- collisionnelle
Adiabaticity breakdown for electron Maxwellian distribution
Breakdown of Adiabaticity For Electrons Transmitted Through A Quasiperpendicular Shock: Part 1- Basic Mechanisms
ABSTRACT
Nonadiabatic Electron Heating and Cooling Through A Self-consistent Quasi-perpendicular Shock. Part 2: A Statistical Analysis
ABSTRACT
Erratum: ``Electron dynamics in two- and one-dimensional oblique supercritical collisionless magnetosonic shocks'' [Journal of Geophysical Research, 99, 6609-6639 (1994)]
Journal of Geophysical Research Atmospheres
Super-Adiabatic and Sub-Adiabatic Electron Heating Through a Quasiperpendicular Supercritical Shock
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.
Impact of the shock front nonstationarity on the formation of adiabatic/nonadiabatic electrons
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.
Adiabaticity breakdown for electrons crossing the stationary/nonstationary front of a collisionless perpendicular shock in supercritical regime
The electron physics of collisionless shocks
Microsintability within the foot of perpendicular supercritical shock: recent PIC simulations
Over and under nonadiabatic electron heating through a perpendicular shock: a statistical approach
Nonstationarity of perpendicular shocks
Nonstationarity of Perpendicular Shock Front: Hybrid Versus PIC Simulations
Dynamics of electrons reflected at collisionless shocks: impact of the shock front turbulence
Reformation of Perpendicular Shocks: 1-D VS 2-D Simulations
ABSTRACT
Breakdown of adiabaticity for electron Maxwellian distribution through a stationary/nonstationary perpendicular supercritical shock
ABSTRACT
Breakdown of electrons adiabaticity: role of nonstationarities in a perpendicular supercritical shock
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
Nonstationarity of two-dimensional supercrititical perpendicular shocks: evidence of competing mechanims
ABSTRACT
1] The shock front nonstationarity of perpendicular shocks in super-critical regime is analyzed b... more 1] The shock front nonstationarity of perpendicular shocks in super-critical regime is analyzed by examining the coupling between ''incoming'' and ''reflected'' ion populations. For a given set of parameters including the upstream Mach number (M A ) and the fraction a of reflected to incoming ions, a self-consistent, time-stationary solution of the coupling between ion streams and the electromagnetic field is sought for. If such a solution is found, the shock is stationary; otherwise, the shock is nonstationary, leading to a self-reforming shock front often observed in full particle simulations of quasiperpendicular shocks. A parametric study of this numerical model allows us to define a critical a crit between stationary and nonstationary regimes. The shock can be nonstationary even for relatively low M A (2-5). For a moderate M A (5-10), the critical value a crit is about 15 to 20%. For very high M A (>10), a crit saturates around 20%. Moreover, present full simulations show that self-reformation of the shock front occurs for relatively low b i and disappears for high b i , where b i is the ratio of upstream ion plasma to magnetic field pressures. Results issued from the present theoretical model are found to be in good agreement with full particle simulations for low b i case; this agreement holds as long as the motion of reflected ions is coherent enough (narrow ion ring) to be described by a single population in the model. The present model reveals to be ''at variance'' with full particle simulations results for the high b i case. Present results are also compared with previous hybrid simulations.
Adiabatic and nonadiabatic electrons through the stationary/ nonstationary front of a collisionless perpendicular shock in supercritical regime