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Masahiro Hoshino - One of the best experts on this subject based on the ideXlab platform.

  • a Critical Mach Number for electron injection in collisionless shocks
    Physical Review Letters, 2010
    Co-Authors: Takanobu Amano, Masahiro Hoshino
    Abstract:

    Electron acceleration in collisionless shocks with arbitrary magnetic field orientations is discussed. It is shown that the injection of thermal electrons into the diffusive shock acceleration process is achieved by an electron beam with a loss cone in velocity space that is reflected back upstream from the shock through the shock drift acceleration mechanism. The electron beam is able to excite whistler waves which can scatter the energetic electrons themselves when the Alfven Mach Number of the shock is sufficiently high. A Critical Mach Number for the electron injection is obtained as a function of upstream parameters. The application to supernova remnant shocks is discussed.

  • strong electron acceleration at high Mach Number shock waves simulation study of electron dynamics
    The Astrophysical Journal, 2000
    Co-Authors: N Shimada, Masahiro Hoshino
    Abstract:

    Electron-ion dynamics in a perpendicular magnetosonic shock wave in a high Mach Number regime is studied by using the particle-in-cell simulation. It is shown that in the shock transition layer nonlinear evolution of two-stream instabilities plays an important role on the electron rapid heating and acceleration. As the shock Mach Number greatly exceeds the Critical Mach Number, a series of large-amplitude, coherent electrostatic waves with the electron holes in phase space are excited by the two-stream instability between the reflected ions and the incident electrons in the shock transition layer. As the incident electrons are decelerated by the instability, other electrostatic waves grow in time by another two-stream instability between the incident ions and the decelerated incident electrons. The dynamic timescale of these instabilities is of the order of ω, where ωpe is the plasma frequency. The nonlinear interaction of these waves leads to the strong electron heating as well as the nonthermal high-energy electron acceleration in the shock transition layer.

M Oka - One of the best experts on this subject based on the ideXlab platform.

  • whistler Critical Mach Number and electron acceleration at the bow shock geotail observation
    Geophysical Research Letters, 2006
    Co-Authors: M Oka, T Terasawa, Y Seki, Masaki Fujimoto, Yasumasa Kasaba, Hirotsugu Kojima, Iku Shinohara, H Matsui
    Abstract:

    [1] The ‘whistler Critical Mach Number’, Mcritw, is one of the dimensionless parameters that characterizes collisionless shocks. Originally, it was introduced to indicate the Critical point above which whistler waves do not propagate upstream. Indeed our analysis of Geotail data at the Earth's bow shock shows intense whistler waves in the sub-Critical regime, MA < Mcritw, but not in the super-Critical regime. In this paper, we further report that Mcritw seems to regulate the electron acceleration efficiency at the shocks. At the shock transition layer it is found that the spectral index Γ of electron energy spectra defined by f(E) ∝ E−Γ is distributed between 3.5 and 5.0 in the sub-Critical regime, while the hardest energy spectra with Γ = 3–3.5 are detected in the super-Critical regime. We discuss a possible relationship between Mcritw and the electron acceleration.

Kang Hyesung - One of the best experts on this subject based on the ideXlab platform.

  • Microinstabilities in the Transition Region of Weak Quasi-Perpendicular Intracluster Shocks
    2021
    Co-Authors: Kim Sunjung, Ha Ji-hoon, Ryu Dongsu, Kang Hyesung
    Abstract:

    Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition zone of quasi-perpendicular ($Q_{\perp}$) shocks in the high-beta ($\beta=P_{\rm gas}/P_{\rm B}$) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfv\'en ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in particle-in-cell (PIC) simulations of $Q_{\perp}$-shocks with sonic Mach Numbers, $M_{\rm s}=2-3$, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including the dependence on $\beta$ and the ion-to-electron mass ratio. In addition, the nonlinear evolution of induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for $\beta\approx 20-100$, the AIC instability could induce ion-scale waves and generate shock surface ripples in superCritical shocks above the AIC Critical Mach Number, $M_{\rm AIC}^{*} \approx 2.3$. Also electron-scale waves are generated primarily by the whistler instability in these high-$\beta$ shocks. The resulting multi-scale waves from electron to ion scales are thought to be essential in electron injection to the diffusive shock acceleration mechanism in $Q_{\perp}$-shocks in the ICM.Comment: 14 pages, 7 figure

  • Microinstabilities in the Transition Region of Weak Quasi-perpendicular Intracluster Shocks
    'American Astronomical Society', 2021
    Co-Authors: Kim Sunjung, Ha Ji-hoon, Ryu Dongsu, Kang Hyesung
    Abstract:

    Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition region of quasi-perpendicular (Q(perpendicular to)) shocks in the high-beta (beta = P-gas/P-B) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfven ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in the particle-in-cell (PIC) simulations of Q(perpendicular to) shocks with sonic Mach Numbers, M-s = 2-3, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including beta and the ion-to-electron mass ratio. In addition, the nonlinear evolution of the induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for beta approximate to 20-100, the AIC instability could induce ion-scale waves and generate shock surface ripples in superCritical shocks above the AIC Critical Mach Number, M-AIC* approximate to 2.3. Also, electron-scale waves are generated primarily by the whistler instability in these high-beta shocks. The resulting multiscale waves from electron to ion scales are thought to be essential in the electron injection to diffusive shock acceleration in Q(perpendicular to) shocks in the ICM

  • Electron Injection in Weak high-beta ICM shocks
    THE AMERICAN ASTRONOMICAL SOCIETY, 2020
    Co-Authors: Kang Hyesung, Ryu Dongsu, Ha Ji-hoon
    Abstract:

    From observations of the so-called radio relics, the electrons are inferred to be accelerated via diffusive shock acceleration (DSA) in low sonic Mach Number shocks induced in the intracluster medium (ICM). Here we study the electron preacceleration and injection to DSA at weak quasi-perpendicular shocks in high beta ICM through 2D PIC simulations. We showed that some of incoming electrons are reflected upstream and gain energy via shock drift acceleration (SDA). The temperature anisotropy due to the SDA-energized backstreaming electrons then induces the electron firehose instability (EFI). Nonpropagating oblique waves are generated in the shock foot, which leads to a Fermi-like process and multiple cycles of SDA in the preshock region. Such electron preacceleration is effective only in shocks above a Critical Mach Number Mef > 2.3. However, electrons may not reach high enough energies to be injected to the full Fermi-I process of DSA, because long-wavelength waves are not self-developed via the EFI alone. Our results indicate that additional electron preaccelerations are required for DSA in ICM shocks, and that the presence of fossil relativistic electrons in the shock upstream region may be necessary to explain observed radio relics unless there are pre-existing turbulent waves longer than the EFI-driven waves

Takanobu Amano - One of the best experts on this subject based on the ideXlab platform.

  • a Critical Mach Number for electron injection in collisionless shocks
    Physical Review Letters, 2010
    Co-Authors: Takanobu Amano, Masahiro Hoshino
    Abstract:

    Electron acceleration in collisionless shocks with arbitrary magnetic field orientations is discussed. It is shown that the injection of thermal electrons into the diffusive shock acceleration process is achieved by an electron beam with a loss cone in velocity space that is reflected back upstream from the shock through the shock drift acceleration mechanism. The electron beam is able to excite whistler waves which can scatter the energetic electrons themselves when the Alfven Mach Number of the shock is sufficiently high. A Critical Mach Number for the electron injection is obtained as a function of upstream parameters. The application to supernova remnant shocks is discussed.

Ha Ji-hoon - One of the best experts on this subject based on the ideXlab platform.

  • Microinstabilities in the Transition Region of Weak Quasi-Perpendicular Intracluster Shocks
    2021
    Co-Authors: Kim Sunjung, Ha Ji-hoon, Ryu Dongsu, Kang Hyesung
    Abstract:

    Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition zone of quasi-perpendicular ($Q_{\perp}$) shocks in the high-beta ($\beta=P_{\rm gas}/P_{\rm B}$) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfv\'en ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in particle-in-cell (PIC) simulations of $Q_{\perp}$-shocks with sonic Mach Numbers, $M_{\rm s}=2-3$, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including the dependence on $\beta$ and the ion-to-electron mass ratio. In addition, the nonlinear evolution of induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for $\beta\approx 20-100$, the AIC instability could induce ion-scale waves and generate shock surface ripples in superCritical shocks above the AIC Critical Mach Number, $M_{\rm AIC}^{*} \approx 2.3$. Also electron-scale waves are generated primarily by the whistler instability in these high-$\beta$ shocks. The resulting multi-scale waves from electron to ion scales are thought to be essential in electron injection to the diffusive shock acceleration mechanism in $Q_{\perp}$-shocks in the ICM.Comment: 14 pages, 7 figure

  • Microinstabilities in the Transition Region of Weak Quasi-perpendicular Intracluster Shocks
    'American Astronomical Society', 2021
    Co-Authors: Kim Sunjung, Ha Ji-hoon, Ryu Dongsu, Kang Hyesung
    Abstract:

    Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition region of quasi-perpendicular (Q(perpendicular to)) shocks in the high-beta (beta = P-gas/P-B) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfven ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in the particle-in-cell (PIC) simulations of Q(perpendicular to) shocks with sonic Mach Numbers, M-s = 2-3, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including beta and the ion-to-electron mass ratio. In addition, the nonlinear evolution of the induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for beta approximate to 20-100, the AIC instability could induce ion-scale waves and generate shock surface ripples in superCritical shocks above the AIC Critical Mach Number, M-AIC* approximate to 2.3. Also, electron-scale waves are generated primarily by the whistler instability in these high-beta shocks. The resulting multiscale waves from electron to ion scales are thought to be essential in the electron injection to diffusive shock acceleration in Q(perpendicular to) shocks in the ICM

  • Electron Injection in Weak high-beta ICM shocks
    THE AMERICAN ASTRONOMICAL SOCIETY, 2020
    Co-Authors: Kang Hyesung, Ryu Dongsu, Ha Ji-hoon
    Abstract:

    From observations of the so-called radio relics, the electrons are inferred to be accelerated via diffusive shock acceleration (DSA) in low sonic Mach Number shocks induced in the intracluster medium (ICM). Here we study the electron preacceleration and injection to DSA at weak quasi-perpendicular shocks in high beta ICM through 2D PIC simulations. We showed that some of incoming electrons are reflected upstream and gain energy via shock drift acceleration (SDA). The temperature anisotropy due to the SDA-energized backstreaming electrons then induces the electron firehose instability (EFI). Nonpropagating oblique waves are generated in the shock foot, which leads to a Fermi-like process and multiple cycles of SDA in the preshock region. Such electron preacceleration is effective only in shocks above a Critical Mach Number Mef > 2.3. However, electrons may not reach high enough energies to be injected to the full Fermi-I process of DSA, because long-wavelength waves are not self-developed via the EFI alone. Our results indicate that additional electron preaccelerations are required for DSA in ICM shocks, and that the presence of fossil relativistic electrons in the shock upstream region may be necessary to explain observed radio relics unless there are pre-existing turbulent waves longer than the EFI-driven waves