Masahiro Hoshino - Profile on Academia.edu (original) (raw)

Papers by Masahiro Hoshino

Research paper thumbnail of Magnetoluminescence

Space Science Reviews, Jun 12, 2017

Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain regions where the electr... more Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain regions where the electromagnetic energy density greatly exceeds the plasma energy density. These sources exhibit dramatic flaring activity where the electromagnetic energy distributed over large volumes, appears to be converted efficiently into high energy particles and γ-rays. We call this general process magnetoluminescence. Global requirements on the underlying, extreme particle acceleration processes are described and the likely importance of relativistic beaming in enhancing the observed radiation from a flare is emphasized. Recent research on fluid descriptions of unstable electromagnetic configurations are summarized and progress on the associated kinetic simulations that are needed to account for the acceleration and radiation is discussed. Future observational, simulation and experimental opportunities are briefly summarized.

Research paper thumbnail of Efficiency of nonthermal particle acceleration in magnetic reconnection

Physics of Plasmas, Apr 1, 2022

The nonthermal particle acceleration during magnetic reconnection remains a fundamental topic in ... more The nonthermal particle acceleration during magnetic reconnection remains a fundamental topic in several astrophysical phenomena, such as solar flares, pulsar wind, magnetars, etc, for more than half a century, and one of the unresolved questions is its efficiency. Recently, nonthermal particle acceleration mechanisms during reconnection have been extensively studied by particle-in-cell simulations, yet it is an intriguing enigma as to how the magnetic field energy is divided into thermally heated plasmas and nonthermal particles. Here we study both non-relativistic and relativistic magnetic reconnections using large-scale particle-in-cell simulation for a pair plasma, and indicate that the production of the nonthermal particle becomes efficient with increasing the plasma temperature. In the relativistic hot plasma case, we determine that the heated plasmas by reconnection can be approximated by a kappa distribution function with the kappa index of approximately 3 or less (equivalent to 2 or less for the power-law index), and the nonthermal energy density of reconnection is approximately over 95% of the total internal energy in the downstream exhaust.

Research paper thumbnail of Instability of Non-Uniform Toroidal Magnetic Fields in Accretion Disks

The Astrophysical Journal, May 10, 2016

A new type of instability that is expected to drive magnetohydrodynamic (MHD) turbulence from a p... more A new type of instability that is expected to drive magnetohydrodynamic (MHD) turbulence from a purely toroidal magnetic field in an accretion disk is presented. It is already known that in a differentially rotating system, the uniform toroidal magnetic field is unstable due to a magnetorotational instability (MRI) under a non-axisymmetric and vertical perturbation, while it is stable under a purely vertical perturbation. Contrary to the previous study, this paper proposes an unstable mode completely confined to the equatorial plane, driven by the expansive nature of the magnetic pressure gradient force under a non-uniform toroidal field. The basic nature of this growing eigenmode, to which we give a name "magneto-gradient driven instability", is studied using linear analysis, and the corresponding nonlinear evolution is then investigated using two-dimensional ideal MHD simulations. Although a single localized magnetic field channel alone cannot provide sufficient Maxwell stress to contribute significantly to the angular momentum transport, we find that the mode coupling between neighboring toroidal fields under multiple localized magnetic field channels drastically generates a highly turbulent state and leads to the enhanced transport of angular momentum, comparable to the efficiency seen in previous studies on MRIs. This horizontally confined mode may play an important role in the saturation of an MRI through complementray growth with the toroidal MHDs and coupling with magnetic reconnection.

Research paper thumbnail of Magnetic reconnection under anisotropic magnetohydrodynamic approximation

Physics of Plasmas, Nov 1, 2013

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one-an... more We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one-and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p || > p ⊥) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10 − 30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system, and is consistent with the satellite observation in the Earth's magnetosphere.

Research paper thumbnail of Nonlinear evolution of plasmoid structure

Earth, Planets and Space, Jun 1, 2001

The plasmoid observed in the Earth's magnetotail shows a wide variety of the complicated plasma s... more The plasmoid observed in the Earth's magnetotail shows a wide variety of the complicated plasma structures that are not simply described by the standard Petschek reconnection model. The interaction of the plasmoid propagating tailward with the surrounding plasmas of the plasma sheet at rest may be important to understand the plasma sheet structure and the plasma heating observed in the magnetotail. The nonlinear time evolution of the plasmoid is studied by using a large-scale, high-resolution, two dimensional MHD simulation code. Several discontinuities/shocks are formed in association with magnetic reconnection: 1) a pair of the standard Petscheck-type slow shock waves emanating from the X-type neutral point, 2) the tangential discontinuity inside the plasmoid that separates the accelerated plasmas from the original plasma sheet plasmas, 3) the slow shock with a "crab-hand" structure surrounding the front-side of the plasmoid, 4) the intermediate shocks in the edge of the plasma sheet inside the plasmoid, and 5) the contact discontinuity inside the plasma sheet that separates the shock-heated plasmas from the Joule heated plasmas by the magnetic diffusion at the X-type neutral point. We also discuss how those plasma discontinuities/shocks structures are affected by the lobe/mantle plasma condition.

Research paper thumbnail of Global characteristics of electron and ion temperatures in the plasma sheet

Japan Geoscience Union, Mar 14, 2018

Research paper thumbnail of Nonlinear explosive magnetic reconnection in a collisionless system

Physics of Plasmas, Jun 1, 2021

The debate surrounding fast magnetic energy dissipation by magnetic reconnection has remained a f... more The debate surrounding fast magnetic energy dissipation by magnetic reconnection has remained a fundamental topic in the plasma universe, not only in the Earth's magnetosphere but in astrophysical objects such as pulsar magnetospheres and magnetars, for more than half a century. Recently, nonthermal particle acceleration and plasma heating during reconnection have been extensively studied, and it has been argued that rapid energy dissipation can occur for a collisionless "thin" current sheet, the thickness of which is of the order of the particle gyro-radius. However, it is an intriguing enigma as to how the fast energy dissipation can occur for a "thick" current sheet with thickness larger than the particle gyro-radius. Here we demonstrate, using a high-resolution particle-in-cell simulation for a pair plasma, that an explosive reconnection can emerge with the enhancement of the inertia resistivity due to the magnetization of the meandering particles by the reconnecting magnetic field and the shrinkage of the current sheet. In addition, regardless of the initial thickness of the current sheet, the time scale of the nonlinear explosive reconnection is tens of the Alfvén transit time.

Research paper thumbnail of Asymmetric evolution of magnetic reconnection in collisionless accretion disk

Physics of Plasmas, May 1, 2014

An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a... more An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J 0 ×Ω 0 where J 0 is the initial current density in the neutral sheet and Ω 0 is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

Research paper thumbnail of PIC simulation methods for cosmic radiation and plasma instabilities

Progress in Particle and Nuclear Physics, Mar 1, 2020

Particle acceleration in collisionless plasma systems is a central question in astroplasma and as... more Particle acceleration in collisionless plasma systems is a central question in astroplasma and astroparticle physics. The structure of the acceleration regions, electron-ion energy equilibration, preacceleration of particles at shocks to permit further energization by diffusive shock acceleration, require knowledge of the distribution function of particles besides the structure and dynamic of electromagnetic fields, and hence a kinetic description is desirable. Particle-in-cell simulations offer an appropriate, if computationally expensive method of essentially conducting numerical experiments that explore kinetic phenomena in collisionless plasma. We review recent results of PIC simulations of astrophysical plasma systems, particle acceleration, and the instabilities that shape them.

Research paper thumbnail of Nonthermal Particle Acceleration in Shock Front Region: “Shock Surfing Accelerations

Progress of theoretical physics. Supplement, 2001

It is believed that the supra-thermal particle acceleration as well as the plasma thermalization ... more It is believed that the supra-thermal particle acceleration as well as the plasma thermalization occurs in the neighborhood of collisionless shock front regions through the interaction of particles with the electrostatic and electromagnetic waves excited by a wide variety of plasma instabilities. In this paper, supra-thermal particle acceleration for a perpendicular magnetosonic shock is discussed by focusing on the interaction of particles with a large amplitude solitary wave formed in the shock front region/shock transition layer. The shock front region was thought to be highly turbulent, but in addition to such a turbulence, a series of large-amplitude, small-scale solitary waves embedded in the shock transition layer are observed by the modern satellites' observations in the earth's bow shock. Motivated by the discovery of the small-scale solitary waves, we study their effect on the particle acceleration by using the particle-in-cell simulations. We study first a non-relativistic, high Mach number shock whose composition consists of ion and electron. We find that the electrostatic solitary waves are excited in the ion-electron shocks by a two-stream instability between the incoming electrons and the reflected ions from the shock front. We discuss that the electrons trapped by the solitary wave can resonate with the shock motional electric field in the shock transition layer, and the so-called shock surfing mechanism is effective for producing the non-thermal, high-energy electrons. We show that the trapped electron can be accelerated up to the shock potential energy determined by a global shock size when the Alfvén Mach number MA exceeds 10 ∼ 100. Next we investigate a relativistic shock whose plasma composition consists of electron and positron, i.e., pair plasma. We discuss that a magnetosonic solitary wave can take the place of the electrostatic solitary wave in the ion-electron shocks. As decreasing σ of the ratio of the upstream Poyinting flux to the upstream kinetic energy flux, the magnetosonic solitary wave forms the current sheet in the shock transition layer, which in turn can trap the particles in the magnetic null region. We discuss that the shock surfing acceleration in a relativistic electron-positron shock occurs under the interaction of the trapped particles by the magnetosonic solitary wave with the shock motional electric field. The trapped particle can be efficiently accelerated up to the shock potential energy determined by a global shock size.

Research paper thumbnail of Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas

The Astrophysical Journal, Nov 20, 2007

We study linear and nonlinear development of relativistic and ultrarelativistic current sheets of... more We study linear and nonlinear development of relativistic and ultrarelativistic current sheets of pair (e ±) plasmas with antiparallel magnetic fields. Two types of two-dimensional problems are investigated by particle-in-cell simulations. First, we present the development of relativistic magnetic reconnection, whose outflow

Research paper thumbnail of Correlated Relativistic Current Sheet Systems

Bulletin of the American Physical Society, Nov 14, 2007

Submitted for the DPP07 Meeting of The American Physical Society Correlated Relativistic Current ... more Submitted for the DPP07 Meeting of The American Physical Society Correlated Relativistic Current Sheet Systems CLAUS JAROSCHEK, MASAHIRO HOSHINO, The University of Tokyo-We study the non-linear evolution of interacting Relativistic Current Sheets (RCS) in 1D/2D/3D self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The intention is to extend the existing knowledge about individual RCS in pair plasma-where the physics is determined by the relativistic tearing and drift kink modes as competing RCS instabilities-towards a correlated RCS system. Such RCS systems are the key element of generic 'striped wind' configurations proposed to model relativistic plasma flows like pulsar winds and gamma-ray bursts. Interactions are enforced in head-on collisions of systems consisting of up to ten individual and equi-distantly separated RCS. The global dynamics divides into a weakly and strongly correlated regime. In the weakly correlated case each RCS persists as an entity and non-thermal particle generation is attributed to a stochastic Fermi-type acceleration mechanism. In the complementary strongly correlated regime the RCS interpenetrate thouroughly and efficient magnetic field dissipation is observed within a 1D stratification. Localized regions persist where the electric supersedes the magnetic field, i.e. the transformation of particle orbits towards a de Hoffmann-Teller-frame is then inherently impossible.

Research paper thumbnail of Transport Ratios of the Kinetic Alfvén Mode in Space Plasmas

Frontiers in Physics, May 29, 2020

Fluctuation properties of the kinetic Alfvén mode, such as polarization of the wave electric and ... more Fluctuation properties of the kinetic Alfvén mode, such as polarization of the wave electric and magnetic field around the mean magnetic field, parallel fluctuation to the mean field, ratios of the electric to magnetic field, and density fluctuations are analytically estimated by constructing the dielectric tensor of plasma based on the linear Vlasov theory. The dielectric tensor contains various fluid-picture processes in the lowest order, including polarization drift, Hall current, and diamagnetic current. Major discoveries from the dielectric tensor method in the kinetic Alfvén mode study are (1) identification of the mechanism of the field rotation sense reversal as a result of competition between the Hall and diamagnetic currents, (2) behavior of the parallel magnetic field fluctuation (in the compressive sense). The analytic expression of transport ratios serves as a diagnostic tool to study and identify the kinetic Alfvén mode in space plasma observations in the inner heliospheric domain.

Research paper thumbnail of Substitution effects in elastic electron collisions with CH3X (X=F, Cl, Br, I) molecules

Journal of Chemical Physics, Feb 19, 2010

We report absolute elastic differential, integral, and momentum transfer cross sections for elect... more We report absolute elastic differential, integral, and momentum transfer cross sections for electron interactions with the series of molecules CH 3 X ͑X = F, Cl, Br, I͒. The incident electron energy range is 50-200 eV, while the scattered electron angular range for the differential measurements is 15°-150°. In all cases the absolute scale of the differential cross sections was set using the relative flow method with helium as the reference species. Substitution effects on these cross sections, as we progress along the halomethane series CH 3 F, CH 3 Cl, CH 3 Br, and CH 3 I, are investigated as a part of this study. In addition, atomic-like behavior in these scattering systems is also considered by comparing these halomethane elastic cross sections to results from other workers for the corresponding noble gases Ne, Ar, Kr, and Xe, respectively. Finally we report results for calculations of elastic differential and integral cross sections for electrons scattering from each of the CH 3 X species, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements was found to be quite remarkable in each case.

Research paper thumbnail of Elastic cross sections for electron scattering from GeF<sub>4</sub>: Predominance of atomic-F in the high-energy collision dynamics

Journal of Chemical Physics, Apr 4, 2012

We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF 4.... more We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF 4. The incident electron energy range was 3-200 eV, while the scattered electron angular range was typically 15 •-150 •. In addition, corresponding independent atom model (IAM) calculations, within the screened additivity rule (SCAR) formulation, were also performed. Those results, particularly for electron energies above about 10 eV, were found to be in good quantitative agreement with the present experimental data. Furthermore, we compare our GeF 4 elastic DCSs to similar data for scattering from CF 4 and SiF 4. All these three species possess T d symmetry, and at each specific energy considered above about 50 eV their DCSs are observed to be almost identical. These indistinguishable features suggest that high-energy elastic scattering from these targets is virtually dominated by the atomic-F species of the molecules. Finally, estimates for the measured GeF 4 elastic integral cross sections are derived and compared to our IAM-SCAR computations and with independent total cross section values.

Research paper thumbnail of Energetic ion acceleration during magnetic reconnection in the Earth’s magnetotail

Earth, Planets and Space, Dec 1, 2015

In this paper, we present a comprehensive study of the energetic ion acceleration during magnetic... more In this paper, we present a comprehensive study of the energetic ion acceleration during magnetic reconnection in the Earth's magnetosphere using the Geotail data. A clear example of the energetic ion acceleration up to 1 MeV around an X-type neutral line is shown. We find that the energetic ions are localized at far downstream of reconnection outflow. The time variation of energetic ion and electron is almost the same. We observe ∼100 keV ions over the entire observation period. We study ten events in which the Geotail satellite observed in the vicinity of diffusion region in order to understand the reconnection characteristics that determine the energetic ion acceleration efficiency. We find that the reconnection electric field, total amount of reduced magnetic energy, reconnection rate, satellite location in the Earth's magnetosphere (both X GSM and Y GSM) show high correlation with energetic ion acceleration efficiency. Also, ion temperature, electron temperature, ion/electron temperature ratio, current sheet thickness, and electric field normal to the neutral sheet show low correlation. We do not find any correlation with absolute value of outflow velocity and current density parallel to magnetic field. The energetic ion acceleration efficiency is well correlated with large-scale parameters (e.g., total amount of reduced magnetic energy and satellite location), whereas the energetic electron acceleration efficiency is correlated with small-scale parameters (e.g., current sheet thickness and electric field normal to the neutral sheet). We conclude that the spatial size of magnetic reconnection is important for energetic ion acceleration in the Earth's magnetotail.

Research paper thumbnail of The Role of the Guide Field in Relativistic Pair Plasma Reconnection

The Astrophysical Journal, Apr 10, 2008

We study the role of the guide field in relativistic magnetic reconnection in a Harris current sh... more We study the role of the guide field in relativistic magnetic reconnection in a Harris current sheet of pair (e ±) plasmas, using linear theories and particlein-cell (PIC) simulations. Two-dimensional PIC simulations exhibit the guide field dependence to the linear instabilities; the tearing or reconnection modes are relatively insensitive, while the relativistic drift-kink instability (RDKI), the fastest mode in a relativistic current sheet, is stabilized by the guide field. Particle acceleration in the nonlinear stage is also investigated. A three-dimensional PIC simulation demonstrates that the current sheet is unstable to the RDKI, although a small reconnection occurs in the deformed current sheet. Another three-dimensional PIC simulation with a guide field demonstrates a completely different scenario. Secondary magnetic reconnection is triggered by nonlinear coupling of oblique instabilities, which we call the relativistic drift-sausage tearing instability. Therefore, particle acceleration by relativistic guide field reconnection occurs in three-dimensional configuration. Based on the plasma theories, we discuss an important role of the guide field: to enable non-thermal particle acceleration by magnetic reconnection.

Research paper thumbnail of Magnetoluminescence

Magnetoluminescence

Space sciences series of ISSI, 2017

Research paper thumbnail of Particle energization in space plasmas: towards a multi-point, multi-scale plasma observatory

Experimental Astronomy, Dec 4, 2021

This White Paper outlines the importance of addressing the fundamental science theme "How are cha... more This White Paper outlines the importance of addressing the fundamental science theme "How are charged particles energized in space plasmas" through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field.

Research paper thumbnail of Magnetic reconnection driven by electron dynamics

Nature Communications, Nov 30, 2018

Magnetic reconnections play essential roles in space, astrophysical, and laboratory plasmas, wher... more Magnetic reconnections play essential roles in space, astrophysical, and laboratory plasmas, where the anti-parallel magnetic field components reconnect and the magnetic energy is converted to the plasma energy as Alfvénic out flows. Although the electron dynamics is considered to be essential, it is highly challenging to observe electron scale reconnections. Here we show the experimental results on an electron scale reconnection driven by the electron dynamics in laser-produced plasmas. We apply a weak-external magnetic field in the direction perpendicular to the plasma propagation, where the magnetic field is directly coupled with only the electrons but not for the ions. Since the kinetic pressure of plasma is much larger than the magnetic pressure, the magnetic field is distorted and locally antiparallel. We observe plasma collimations, cusp and plasmoid like features with optical diagnostics. The plasmoid propagates at the electron Alfvén velocity, indicating a reconnection driven by the electron dynamics.

Research paper thumbnail of Magnetoluminescence

Space Science Reviews, Jun 12, 2017

Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain regions where the electr... more Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain regions where the electromagnetic energy density greatly exceeds the plasma energy density. These sources exhibit dramatic flaring activity where the electromagnetic energy distributed over large volumes, appears to be converted efficiently into high energy particles and γ-rays. We call this general process magnetoluminescence. Global requirements on the underlying, extreme particle acceleration processes are described and the likely importance of relativistic beaming in enhancing the observed radiation from a flare is emphasized. Recent research on fluid descriptions of unstable electromagnetic configurations are summarized and progress on the associated kinetic simulations that are needed to account for the acceleration and radiation is discussed. Future observational, simulation and experimental opportunities are briefly summarized.

Research paper thumbnail of Efficiency of nonthermal particle acceleration in magnetic reconnection

Physics of Plasmas, Apr 1, 2022

The nonthermal particle acceleration during magnetic reconnection remains a fundamental topic in ... more The nonthermal particle acceleration during magnetic reconnection remains a fundamental topic in several astrophysical phenomena, such as solar flares, pulsar wind, magnetars, etc, for more than half a century, and one of the unresolved questions is its efficiency. Recently, nonthermal particle acceleration mechanisms during reconnection have been extensively studied by particle-in-cell simulations, yet it is an intriguing enigma as to how the magnetic field energy is divided into thermally heated plasmas and nonthermal particles. Here we study both non-relativistic and relativistic magnetic reconnections using large-scale particle-in-cell simulation for a pair plasma, and indicate that the production of the nonthermal particle becomes efficient with increasing the plasma temperature. In the relativistic hot plasma case, we determine that the heated plasmas by reconnection can be approximated by a kappa distribution function with the kappa index of approximately 3 or less (equivalent to 2 or less for the power-law index), and the nonthermal energy density of reconnection is approximately over 95% of the total internal energy in the downstream exhaust.

Research paper thumbnail of Instability of Non-Uniform Toroidal Magnetic Fields in Accretion Disks

The Astrophysical Journal, May 10, 2016

A new type of instability that is expected to drive magnetohydrodynamic (MHD) turbulence from a p... more A new type of instability that is expected to drive magnetohydrodynamic (MHD) turbulence from a purely toroidal magnetic field in an accretion disk is presented. It is already known that in a differentially rotating system, the uniform toroidal magnetic field is unstable due to a magnetorotational instability (MRI) under a non-axisymmetric and vertical perturbation, while it is stable under a purely vertical perturbation. Contrary to the previous study, this paper proposes an unstable mode completely confined to the equatorial plane, driven by the expansive nature of the magnetic pressure gradient force under a non-uniform toroidal field. The basic nature of this growing eigenmode, to which we give a name "magneto-gradient driven instability", is studied using linear analysis, and the corresponding nonlinear evolution is then investigated using two-dimensional ideal MHD simulations. Although a single localized magnetic field channel alone cannot provide sufficient Maxwell stress to contribute significantly to the angular momentum transport, we find that the mode coupling between neighboring toroidal fields under multiple localized magnetic field channels drastically generates a highly turbulent state and leads to the enhanced transport of angular momentum, comparable to the efficiency seen in previous studies on MRIs. This horizontally confined mode may play an important role in the saturation of an MRI through complementray growth with the toroidal MHDs and coupling with magnetic reconnection.

Research paper thumbnail of Magnetic reconnection under anisotropic magnetohydrodynamic approximation

Physics of Plasmas, Nov 1, 2013

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one-an... more We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one-and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observations. Our results showed that once magnetic reconnection takes place, a firehose-sense (p || > p ⊥) pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10 − 30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system, and is consistent with the satellite observation in the Earth's magnetosphere.

Research paper thumbnail of Nonlinear evolution of plasmoid structure

Earth, Planets and Space, Jun 1, 2001

The plasmoid observed in the Earth's magnetotail shows a wide variety of the complicated plasma s... more The plasmoid observed in the Earth's magnetotail shows a wide variety of the complicated plasma structures that are not simply described by the standard Petschek reconnection model. The interaction of the plasmoid propagating tailward with the surrounding plasmas of the plasma sheet at rest may be important to understand the plasma sheet structure and the plasma heating observed in the magnetotail. The nonlinear time evolution of the plasmoid is studied by using a large-scale, high-resolution, two dimensional MHD simulation code. Several discontinuities/shocks are formed in association with magnetic reconnection: 1) a pair of the standard Petscheck-type slow shock waves emanating from the X-type neutral point, 2) the tangential discontinuity inside the plasmoid that separates the accelerated plasmas from the original plasma sheet plasmas, 3) the slow shock with a "crab-hand" structure surrounding the front-side of the plasmoid, 4) the intermediate shocks in the edge of the plasma sheet inside the plasmoid, and 5) the contact discontinuity inside the plasma sheet that separates the shock-heated plasmas from the Joule heated plasmas by the magnetic diffusion at the X-type neutral point. We also discuss how those plasma discontinuities/shocks structures are affected by the lobe/mantle plasma condition.

Research paper thumbnail of Global characteristics of electron and ion temperatures in the plasma sheet

Japan Geoscience Union, Mar 14, 2018

Research paper thumbnail of Nonlinear explosive magnetic reconnection in a collisionless system

Physics of Plasmas, Jun 1, 2021

The debate surrounding fast magnetic energy dissipation by magnetic reconnection has remained a f... more The debate surrounding fast magnetic energy dissipation by magnetic reconnection has remained a fundamental topic in the plasma universe, not only in the Earth's magnetosphere but in astrophysical objects such as pulsar magnetospheres and magnetars, for more than half a century. Recently, nonthermal particle acceleration and plasma heating during reconnection have been extensively studied, and it has been argued that rapid energy dissipation can occur for a collisionless "thin" current sheet, the thickness of which is of the order of the particle gyro-radius. However, it is an intriguing enigma as to how the fast energy dissipation can occur for a "thick" current sheet with thickness larger than the particle gyro-radius. Here we demonstrate, using a high-resolution particle-in-cell simulation for a pair plasma, that an explosive reconnection can emerge with the enhancement of the inertia resistivity due to the magnetization of the meandering particles by the reconnecting magnetic field and the shrinkage of the current sheet. In addition, regardless of the initial thickness of the current sheet, the time scale of the nonlinear explosive reconnection is tens of the Alfvén transit time.

Research paper thumbnail of Asymmetric evolution of magnetic reconnection in collisionless accretion disk

Physics of Plasmas, May 1, 2014

An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a... more An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J 0 ×Ω 0 where J 0 is the initial current density in the neutral sheet and Ω 0 is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

Research paper thumbnail of PIC simulation methods for cosmic radiation and plasma instabilities

Progress in Particle and Nuclear Physics, Mar 1, 2020

Particle acceleration in collisionless plasma systems is a central question in astroplasma and as... more Particle acceleration in collisionless plasma systems is a central question in astroplasma and astroparticle physics. The structure of the acceleration regions, electron-ion energy equilibration, preacceleration of particles at shocks to permit further energization by diffusive shock acceleration, require knowledge of the distribution function of particles besides the structure and dynamic of electromagnetic fields, and hence a kinetic description is desirable. Particle-in-cell simulations offer an appropriate, if computationally expensive method of essentially conducting numerical experiments that explore kinetic phenomena in collisionless plasma. We review recent results of PIC simulations of astrophysical plasma systems, particle acceleration, and the instabilities that shape them.

Research paper thumbnail of Nonthermal Particle Acceleration in Shock Front Region: “Shock Surfing Accelerations

Progress of theoretical physics. Supplement, 2001

It is believed that the supra-thermal particle acceleration as well as the plasma thermalization ... more It is believed that the supra-thermal particle acceleration as well as the plasma thermalization occurs in the neighborhood of collisionless shock front regions through the interaction of particles with the electrostatic and electromagnetic waves excited by a wide variety of plasma instabilities. In this paper, supra-thermal particle acceleration for a perpendicular magnetosonic shock is discussed by focusing on the interaction of particles with a large amplitude solitary wave formed in the shock front region/shock transition layer. The shock front region was thought to be highly turbulent, but in addition to such a turbulence, a series of large-amplitude, small-scale solitary waves embedded in the shock transition layer are observed by the modern satellites' observations in the earth's bow shock. Motivated by the discovery of the small-scale solitary waves, we study their effect on the particle acceleration by using the particle-in-cell simulations. We study first a non-relativistic, high Mach number shock whose composition consists of ion and electron. We find that the electrostatic solitary waves are excited in the ion-electron shocks by a two-stream instability between the incoming electrons and the reflected ions from the shock front. We discuss that the electrons trapped by the solitary wave can resonate with the shock motional electric field in the shock transition layer, and the so-called shock surfing mechanism is effective for producing the non-thermal, high-energy electrons. We show that the trapped electron can be accelerated up to the shock potential energy determined by a global shock size when the Alfvén Mach number MA exceeds 10 ∼ 100. Next we investigate a relativistic shock whose plasma composition consists of electron and positron, i.e., pair plasma. We discuss that a magnetosonic solitary wave can take the place of the electrostatic solitary wave in the ion-electron shocks. As decreasing σ of the ratio of the upstream Poyinting flux to the upstream kinetic energy flux, the magnetosonic solitary wave forms the current sheet in the shock transition layer, which in turn can trap the particles in the magnetic null region. We discuss that the shock surfing acceleration in a relativistic electron-positron shock occurs under the interaction of the trapped particles by the magnetosonic solitary wave with the shock motional electric field. The trapped particle can be efficiently accelerated up to the shock potential energy determined by a global shock size.

Research paper thumbnail of Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas

The Astrophysical Journal, Nov 20, 2007

We study linear and nonlinear development of relativistic and ultrarelativistic current sheets of... more We study linear and nonlinear development of relativistic and ultrarelativistic current sheets of pair (e ±) plasmas with antiparallel magnetic fields. Two types of two-dimensional problems are investigated by particle-in-cell simulations. First, we present the development of relativistic magnetic reconnection, whose outflow

Research paper thumbnail of Correlated Relativistic Current Sheet Systems

Bulletin of the American Physical Society, Nov 14, 2007

Submitted for the DPP07 Meeting of The American Physical Society Correlated Relativistic Current ... more Submitted for the DPP07 Meeting of The American Physical Society Correlated Relativistic Current Sheet Systems CLAUS JAROSCHEK, MASAHIRO HOSHINO, The University of Tokyo-We study the non-linear evolution of interacting Relativistic Current Sheets (RCS) in 1D/2D/3D self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The intention is to extend the existing knowledge about individual RCS in pair plasma-where the physics is determined by the relativistic tearing and drift kink modes as competing RCS instabilities-towards a correlated RCS system. Such RCS systems are the key element of generic 'striped wind' configurations proposed to model relativistic plasma flows like pulsar winds and gamma-ray bursts. Interactions are enforced in head-on collisions of systems consisting of up to ten individual and equi-distantly separated RCS. The global dynamics divides into a weakly and strongly correlated regime. In the weakly correlated case each RCS persists as an entity and non-thermal particle generation is attributed to a stochastic Fermi-type acceleration mechanism. In the complementary strongly correlated regime the RCS interpenetrate thouroughly and efficient magnetic field dissipation is observed within a 1D stratification. Localized regions persist where the electric supersedes the magnetic field, i.e. the transformation of particle orbits towards a de Hoffmann-Teller-frame is then inherently impossible.

Research paper thumbnail of Transport Ratios of the Kinetic Alfvén Mode in Space Plasmas

Frontiers in Physics, May 29, 2020

Fluctuation properties of the kinetic Alfvén mode, such as polarization of the wave electric and ... more Fluctuation properties of the kinetic Alfvén mode, such as polarization of the wave electric and magnetic field around the mean magnetic field, parallel fluctuation to the mean field, ratios of the electric to magnetic field, and density fluctuations are analytically estimated by constructing the dielectric tensor of plasma based on the linear Vlasov theory. The dielectric tensor contains various fluid-picture processes in the lowest order, including polarization drift, Hall current, and diamagnetic current. Major discoveries from the dielectric tensor method in the kinetic Alfvén mode study are (1) identification of the mechanism of the field rotation sense reversal as a result of competition between the Hall and diamagnetic currents, (2) behavior of the parallel magnetic field fluctuation (in the compressive sense). The analytic expression of transport ratios serves as a diagnostic tool to study and identify the kinetic Alfvén mode in space plasma observations in the inner heliospheric domain.

Research paper thumbnail of Substitution effects in elastic electron collisions with CH3X (X=F, Cl, Br, I) molecules

Journal of Chemical Physics, Feb 19, 2010

We report absolute elastic differential, integral, and momentum transfer cross sections for elect... more We report absolute elastic differential, integral, and momentum transfer cross sections for electron interactions with the series of molecules CH 3 X ͑X = F, Cl, Br, I͒. The incident electron energy range is 50-200 eV, while the scattered electron angular range for the differential measurements is 15°-150°. In all cases the absolute scale of the differential cross sections was set using the relative flow method with helium as the reference species. Substitution effects on these cross sections, as we progress along the halomethane series CH 3 F, CH 3 Cl, CH 3 Br, and CH 3 I, are investigated as a part of this study. In addition, atomic-like behavior in these scattering systems is also considered by comparing these halomethane elastic cross sections to results from other workers for the corresponding noble gases Ne, Ar, Kr, and Xe, respectively. Finally we report results for calculations of elastic differential and integral cross sections for electrons scattering from each of the CH 3 X species, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements was found to be quite remarkable in each case.

Research paper thumbnail of Elastic cross sections for electron scattering from GeF<sub>4</sub>: Predominance of atomic-F in the high-energy collision dynamics

Journal of Chemical Physics, Apr 4, 2012

We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF 4.... more We report absolute differential cross sections (DCSs) for elastic electron scattering from GeF 4. The incident electron energy range was 3-200 eV, while the scattered electron angular range was typically 15 •-150 •. In addition, corresponding independent atom model (IAM) calculations, within the screened additivity rule (SCAR) formulation, were also performed. Those results, particularly for electron energies above about 10 eV, were found to be in good quantitative agreement with the present experimental data. Furthermore, we compare our GeF 4 elastic DCSs to similar data for scattering from CF 4 and SiF 4. All these three species possess T d symmetry, and at each specific energy considered above about 50 eV their DCSs are observed to be almost identical. These indistinguishable features suggest that high-energy elastic scattering from these targets is virtually dominated by the atomic-F species of the molecules. Finally, estimates for the measured GeF 4 elastic integral cross sections are derived and compared to our IAM-SCAR computations and with independent total cross section values.

Research paper thumbnail of Energetic ion acceleration during magnetic reconnection in the Earth’s magnetotail

Earth, Planets and Space, Dec 1, 2015

In this paper, we present a comprehensive study of the energetic ion acceleration during magnetic... more In this paper, we present a comprehensive study of the energetic ion acceleration during magnetic reconnection in the Earth's magnetosphere using the Geotail data. A clear example of the energetic ion acceleration up to 1 MeV around an X-type neutral line is shown. We find that the energetic ions are localized at far downstream of reconnection outflow. The time variation of energetic ion and electron is almost the same. We observe ∼100 keV ions over the entire observation period. We study ten events in which the Geotail satellite observed in the vicinity of diffusion region in order to understand the reconnection characteristics that determine the energetic ion acceleration efficiency. We find that the reconnection electric field, total amount of reduced magnetic energy, reconnection rate, satellite location in the Earth's magnetosphere (both X GSM and Y GSM) show high correlation with energetic ion acceleration efficiency. Also, ion temperature, electron temperature, ion/electron temperature ratio, current sheet thickness, and electric field normal to the neutral sheet show low correlation. We do not find any correlation with absolute value of outflow velocity and current density parallel to magnetic field. The energetic ion acceleration efficiency is well correlated with large-scale parameters (e.g., total amount of reduced magnetic energy and satellite location), whereas the energetic electron acceleration efficiency is correlated with small-scale parameters (e.g., current sheet thickness and electric field normal to the neutral sheet). We conclude that the spatial size of magnetic reconnection is important for energetic ion acceleration in the Earth's magnetotail.

Research paper thumbnail of The Role of the Guide Field in Relativistic Pair Plasma Reconnection

The Astrophysical Journal, Apr 10, 2008

We study the role of the guide field in relativistic magnetic reconnection in a Harris current sh... more We study the role of the guide field in relativistic magnetic reconnection in a Harris current sheet of pair (e ±) plasmas, using linear theories and particlein-cell (PIC) simulations. Two-dimensional PIC simulations exhibit the guide field dependence to the linear instabilities; the tearing or reconnection modes are relatively insensitive, while the relativistic drift-kink instability (RDKI), the fastest mode in a relativistic current sheet, is stabilized by the guide field. Particle acceleration in the nonlinear stage is also investigated. A three-dimensional PIC simulation demonstrates that the current sheet is unstable to the RDKI, although a small reconnection occurs in the deformed current sheet. Another three-dimensional PIC simulation with a guide field demonstrates a completely different scenario. Secondary magnetic reconnection is triggered by nonlinear coupling of oblique instabilities, which we call the relativistic drift-sausage tearing instability. Therefore, particle acceleration by relativistic guide field reconnection occurs in three-dimensional configuration. Based on the plasma theories, we discuss an important role of the guide field: to enable non-thermal particle acceleration by magnetic reconnection.

Research paper thumbnail of Magnetoluminescence

Magnetoluminescence

Space sciences series of ISSI, 2017

Research paper thumbnail of Particle energization in space plasmas: towards a multi-point, multi-scale plasma observatory

Experimental Astronomy, Dec 4, 2021

This White Paper outlines the importance of addressing the fundamental science theme "How are cha... more This White Paper outlines the importance of addressing the fundamental science theme "How are charged particles energized in space plasmas" through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field.

Research paper thumbnail of Magnetic reconnection driven by electron dynamics

Nature Communications, Nov 30, 2018

Magnetic reconnections play essential roles in space, astrophysical, and laboratory plasmas, wher... more Magnetic reconnections play essential roles in space, astrophysical, and laboratory plasmas, where the anti-parallel magnetic field components reconnect and the magnetic energy is converted to the plasma energy as Alfvénic out flows. Although the electron dynamics is considered to be essential, it is highly challenging to observe electron scale reconnections. Here we show the experimental results on an electron scale reconnection driven by the electron dynamics in laser-produced plasmas. We apply a weak-external magnetic field in the direction perpendicular to the plasma propagation, where the magnetic field is directly coupled with only the electrons but not for the ions. Since the kinetic pressure of plasma is much larger than the magnetic pressure, the magnetic field is distorted and locally antiparallel. We observe plasma collimations, cusp and plasmoid like features with optical diagnostics. The plasmoid propagates at the electron Alfvén velocity, indicating a reconnection driven by the electron dynamics.