Yasuhiro Nariyuki

A non-oscillatory and conservative semi-Lagrangian scheme with fourth-degree polynomial interpolation for solving the Vlasov equation

Abstract A conservative semi-Lagrangian scheme for the numerical solution of the Vlasov equation is developed based on the fourth-degree polynomial interpolation. Then, a numerical filter is implemented that preserves positivity and non-oscillatory. The numerical results of both one-dimensional linear advection and two-dimensional Vlasov–Poisson simulations show that the numerical diffusion with the fourth-degree polynomial interpolation is suppressed more than with the cubic polynomial interpolation. It is also found that inherent conservation properties of the Vlasov equation can be improved by combining numerical fluxes of the upwind-biased and central fourth-degree polynomial interpolations.

Heating and acceleration of ions in nonresonant Alfvénic turbulence

Nonlinear scattering of protons and alpha particles during the dissipation of the finite amplitude, low-frequency Alfvenic turbulence is studied. The process discussed here is not the coherent scattering and acceleration, as those often treated in the past studies, but is an incoherent process in which it is essential that the Alfvenic turbulence has a broadband spectrum. The presence of such an Alfvenic turbulence is widely recognized observationally both in the solar corona and in the solar wind. Numerical results suggest that, although there is no apparent sign of the occurrence of any parametric instabilities, the ions are heated efficiently by the nonlinear Landau damping, i.e., trapping and phase mixing by Alfven wave packets which are generated by beating of finite amplitude Alfven waves. The heating occurs both in the parallel and in the perpendicular directions, and the ion distribution function which is asymmetric with respect to the parallel velocity is produced. Eventual perpendicular energy o...

ON ELECTRON-SCALE WHISTLER TURBULENCE IN THE SOLAR WIND

For the first time, the dispersion relation for turbulence magnetic field fluctuations in the solar wind is determined directly on small scales of the order of the electron inertial length, using four-point magnetometer observations from the Magnetospheric Multiscale mission. The data are analyzed using the high-resolution adaptive wave telescope technique. Small-scale solar wind turbulence is primarily composed of highly obliquely propagating waves, with dispersion consistent with that of the whistler mode.

A Scalable Full-Electromagnetic Vlasov Solver for Cross-Scale Coupling in Space Plasma

Numerical schemes for solving the Vlasov-Maxwell system equations are studied. For studies of cross-scale coupling between fluid-scale dynamics and particle-scale kinetics in collisionless plasma, both highly scalable kinetic code and huge supercomputer are essential. In the present study, a new parallel Vlasov-Maxwell solver is developed by adopting a stable but less dissipative scheme for time integration of conservation laws. The new code has successfully achieved a high scalability on massively parallel supercomputers with multicore scalar processors. The new code has been applied to 2P3V (two dimensions for position and three dimensions for velocity) problems of cross-scale plasma processes such as magnetic reconnection, Kelvin-Helmholtz instability, and interaction between the solar wind and an asteroid.

Nonlinear dissipation of circularly polarized Alfvén waves due to the beam-induced obliquely propagating waves

In the present study, the dissipation processes of circularly polarized Alfven waves in solar wind plasmas including beam components are numerically discussed by using a 2-D hybrid simulation code. Numerical results suggest that the parent Alfven waves are rapidly dissipated due to the presence of the beam-induced obliquely propagating waves, such as kinetic Alfven waves. The nonlinear wave-wave coupling is directly evaluated by using the induction equation for the parent wave. It is also observed both in the 1-D and 2-D simulations that the presence of large amplitude Alfven waves strongly suppresses the beam instabilities.

Simulation and quasilinear theory of aperiodic ordinary mode instability

The purely growing ordinary (O) mode instability driven by excessive parallel temperature anisotropy for high-beta plasmas was first discovered in the 1970s. This instability receives renewed attention because it may be applicable to the solar wind plasma. The electrons in the solar wind feature temperature anisotropies whose upper values are apparently limited by plasma instabilities. The O-mode instability may be important in this regard. Previous studies of O mode instability have been based on linear theory, but the actual solar wind electrons may be in saturated state. The present paper investigates the nonlinear saturation behavior of the O mode instability by means of one-dimensional particle-in-cell simulation and quasilinear theory. It is shown that the quasilinear method accurately reproduces the simulation results.

Nonlinear damping of a finite amplitude whistler wave due to modified two stream instability

A two-dimensional, fully kinetic, particle-in-cell simulation is used to investigate the nonlinear development of a parallel propagating finite amplitude whistler wave (parent wave) with a wavelength longer than an ion inertial length. The cross field current of the parent wave generates short-scale whistler waves propagating highly oblique directions to the ambient magnetic field through the modified two-stream instability (MTSI) which scatters electrons and ions parallel and perpendicular to the magnetic field, respectively. The parent wave is largely damped during a time comparable to the wave period. The MTSI-driven damping process is proposed as a cause of nonlinear dissipation of kinetic turbulence in the solar wind.

Macroscopic quasi‐linear theory and particle‐in‐cell simulation of helium ion anisotropy instabilities

The protons and helium ions in the solar wind are observed to possess anisotropic temperature profiles. The anisotropy appears to be limited by various marginal instability conditions. One of the efficient methods to investigate the global dynamics and distribution of various temperature anisotropies in the large-scale solar wind models may be that based upon the macroscopic quasi-linear approach. The present paper investigates the proton and helium ion anisotropy instabilities on the basis of the quasi-linear theory versus particle-in-cell simulation. It is found that the overall dynamical development of the particle temperatures is quite accurately reproduced by the macroscopic quasi-linear scheme. The wave energy development in time, however, shows somewhat less restrictive comparisons, indicating that while the quasi-linear method is acceptable for the particle dynamics, the wave analysis probably requires higher-order physics, such as wave-wave coupling or nonlinear wave-particle interaction.

Collisionless damping of circularly polarized nonlinear Alfvén waves in solar wind plasmas with and without beam protons

The damping process of field-aligned, low-frequency right-handed polarized nonlinear Alfven waves (NAWs) in solar wind plasmas with and without proton beams is studied by using a two-dimensional ion hybrid code. The numerical results show that the obliquely propagating kinetic Alfven waves (KAWs) excited by beam protons affect the damping of the low-frequency NAW in low beta plasmas, while the nonlinear wave-wave interaction between parallel propagating waves and nonlinear Landau damping due to the envelope modulation are the dominant damping process in high beta plasmas. The nonlinear interaction between the NAWs and KAWs does not cause effective energy transfer to the perpendicular direction. Numerical results suggest that while the collisionless damping due to the compressibility of the envelope-modulated NAW plays an important role in the damping of the field-aligned NAW, the effect of the beam instabilities may not be negligible in low beta solar wind plasmas.

On entropy-maximized velocity distributions in circularly polarized finite amplitude Alfvén waves

A special solution of the Vlasov-Maxwell system, which represents a circularly polarized Alfven wave, is derived as an entropy-maximized state. It is shown that Alfvenic correlation between transverse bulk motion and magnetic field given by the entropy-maximized distribution is consistent with the equilibrium point of the single particle system. We demonstrate that as far as the monochromatic, circularly polarized magnetic field is concerned, the resultant distribution may be a relaxed state corresponding to one in the Hall-magnetohydrodynamic system. Stability of the distribution function is numerically discussed by using an ion-hybrid simulation code. Numerical results suggest that the relaxed states in nonmonochromatic waves are different from those in monochromatic waves.