5:15 PM - 6:45 PM
[PEM17-P13] Evaluation of saturation level of Buneman instability in relativistic shock waves
Keywords:Relativistic Shock Waves
How high-energy cosmic rays are produced in the universe is still not well understood. The energy distribution of high-energy particles in the universe is known to be a power-law spectrum, and there have been various discussions on how these particles are accelerated. Diffusive shock acceleration used as the standard model. This can explain the power-law spectrum, but problems exist, such as the electron-injection problem. Therefore, we focused on the physics of the shock transition layer to explore the mechanism of the initial acceleration of the particles. It is well known that particles are efficiently accelerated in the shock transition layer. In this study, we focus on Buneman instability, which is the electrostatic instability that occurs when electrons and ions have relative velocities.
[Shimada & Hoshino, 2000] have shown that Buneman instability induces rapid and strong electron heating in the shock transition layer in a non-relativistic regime. Buneman instability has the maximum linear growth rate at the wavenumbers along the beam direction in the non-relativistic regime, but the nature of the linear growth changes in the relativistic regime. In other words, the linear growth rate in the beam direction is suppressed, and the wavenumber with the maximum growth rate changes to an oblique direction with respect to the beam [Dieckmann et al. 2008]. However, nonlinear evolution, especially the wavenumber dependence of the saturation levels and saturation mechanisms, has not been well investigated. Therefore, we employed a local model with periodic boundary conditions to perform Particle-in-Cell (PIC) simulations of the shock transition layer. First, the maximum growth rate predicted by theory was compared with the results of 1D simulations to confirm the Lorenz factor dependence.
In addition, the saturation level of the instability and the wavenumber dominating the power at the saturation were investigated using 2D simulation results. In this presentation, we use these results to discuss the differences in the nonlinear evolution between relativistic and non-relativistic regimes.
[Shimada & Hoshino, 2000] have shown that Buneman instability induces rapid and strong electron heating in the shock transition layer in a non-relativistic regime. Buneman instability has the maximum linear growth rate at the wavenumbers along the beam direction in the non-relativistic regime, but the nature of the linear growth changes in the relativistic regime. In other words, the linear growth rate in the beam direction is suppressed, and the wavenumber with the maximum growth rate changes to an oblique direction with respect to the beam [Dieckmann et al. 2008]. However, nonlinear evolution, especially the wavenumber dependence of the saturation levels and saturation mechanisms, has not been well investigated. Therefore, we employed a local model with periodic boundary conditions to perform Particle-in-Cell (PIC) simulations of the shock transition layer. First, the maximum growth rate predicted by theory was compared with the results of 1D simulations to confirm the Lorenz factor dependence.
In addition, the saturation level of the instability and the wavenumber dominating the power at the saturation were investigated using 2D simulation results. In this presentation, we use these results to discuss the differences in the nonlinear evolution between relativistic and non-relativistic regimes.