Coherent radio waves from pulsars bring information about relativistic extremely-magnetized pair plasmas in neutron star magnetospheres because the waves originate at plasma kinetic scales. Though various radio emission mechanisms have been proposed in the last decades for their interpretation, many lack the inclusion of self-consistent wave--wave and particle--wave interactions, emission...
It is known that magnetic reconnection can occur in current sheets generated by collisionless turbulence in space and astrophysical plasmas, a process known as turbulence-driven reconnection. The importance of this process for the turbulence properties is, however, still not well understood. Although significant simulation work has been done on this topic in 2D and at MHD and ion-scales, the...
We study penetration of interstellar cosmic rays (CRs) into molecular clouds surrounded by nonuniform diffuse envelopes. The present work generalizes our earlier model of CR self-modulation [1,2], in which the value for the envelope's gas density where CRs excite MHD waves was treated as a free parameter. Now, we investigate the case where the density monotonically increases toward the center....
The emerging computable devices, graphical processing units (GPU), are gradually applied in the simulations of space physics for their high efficiency. Here we present a fully kinetic particle-in-cell (PIC) simulation code running on GPU devices called GPIC, which adopts CUDA Fortran programming. Compared with the simulations running on the Intel Xeon Gold processor, our program working on...
Particle-in-cell (PIC) simulation is an important tool to study collective behavior of charged particles in space. At start of the simulation, it is necessary to initialize particle velocities, by using random variables. The distribution of particle velocities may vary from problem to problem. We may want to use a Maxwell distribution in many cases, a kappa distribution for heliospheric...
Numerical methods for solving the relativistic motion of charged particles with a higher accuracy is an issue for scientific computing in various fields including plasma physics. The classic fourth-order Runge-Kutta method (RK4) has been used over many years for tracking charged particle motions, although RK4 does not satisfy any conservation law. However, the Boris method [Boris 1970] has...
I will describe Astrophysical Hybrid-Kinetic simulations with the flASH code (AHKASH) - a new Hybrid particle-in-cell (PIC) module developed within the framework of the multi-physics code FLASH. Our new second-order accurate hybrid PIC method uses the Boris particle integrator and a predictor-predictor-corrector algorithm for advancing the Hybrid-kinetic equations. It also employs the...
Particle-in-Cell simulations can provide a possible answer to an important key issue of astrophysical plasma jets, i.e., how a toroidal magnetic field affects the evolution of pair and electron-ion jets associated to the acceleration of particles. We show that Weibel, mushroom, and kinetic Kelvin-Helmholtz instabilities excited at the linear stage, generate a quasi-steady electric field...
Despite significant strides in numerical and theoretical understanding, the active galactic nucleus (AGN) jet structure is still an open question. Relativistic magnetohydrodynamical (RMHD) simulations are indispensable tools for probing the dynamics and emission of these astrophysical sources. Recent attention has shifted towards investigating instabilities downstream of recollimation shocks,...
The heat flux of electrons plays a crucial role in energy transport processes in collisionless or weakly collisional plasma of the solar wind. Early observations indicated that the collisional Spitzer-Hรคrm law cannot describe the heat flux in the solar wind. Various mechanisms for regulating heat flux in the solar wind have been proposed, such as the interaction of electrons with whistler...
The correlation between linear and nonlinear ion acoustic waves (IAWs); i.e. solitary waves, observed in the vicinity to the Sun is still an open question. These electrostatic structures have a high electric field and are regularly spaced (Mozer et al. 2021; Graham et al. 2021). We study the onset of the ion acoustic instability in a parameter regime compatible with these observations. In the...
During magnetospheric substorms, plasma from magnetic reconnection in the magnetotail is thought to reach the inner magnetosphere and form a partial ring current. We simulate this process using a fully kinetic particle-in-cell (PIC) numerical code starting from a global magnetohydrodynamics (MHD) model run for nominal solar wind parameters and a southward interplanetary magnetic field. The PIC...
The interactions between the solar wind and planetary magnetospheres dictate the planetary space environments. Three-dimensional global hybrid simulations allow us to better understand such interactions by considering particle kinetic effects in global configurations. I will talk about some of our simulation results for Earth's and Mercury's magnetospheres, including 1) Flux ropes and their...
Global simulations have become an invaluable tool for studies of planetary magnetospheres, aiding in interpreting satellite observations, uncovering new physics and processes, and deepening our understanding of the fundamental magnetospheric behavior. Because of their relatively large system sizes, planetary magnetospheres are normally simulated with ideal magnetohydrodynamics (MHD) models,...
Analytical and numerical models of the linear and nonlinear stages of evolution of different types of short scale low frequency waves in the mid-latitude ionosphere will be presented. Density gradients and velocity shears observed in the Earthโs ionosphere are likely to undergo Raleigh-Taylor (RT) or Kelvin-Helmholtz (KH) type instabilities, but typically live longer than expected. Possibility...
We present a physical mechanism for generating GeV protons in the Inner Jovian Magnetosphere [1], which may contribute to formation of the proton radiation belts. The mechanism consists of two nonlinear processes called anomalous trapping and relativistic turning acceleration (RTA) and involves a special form of nonlinear wave trapping by electromagnetic ion cyclotron (EMIC) waves. Necessary...
The dynamics of Bursty Bulk Flows (BBFs) is an outstanding magnetosphere-ionosphere-thermosphere (MIT) coupling problem associated with sudden magnetic field topology reconfiguration and explosive current formation, particle acceleration, and energy release in the magnetosphere, and is believed to be playing a central role in geomagnetic disturbances, such as substorms. Using a two-way coupled...
Langmuir probes are essential diagnostic instruments used in laboratory plasma experiments and space missions. While traditional Langmuir probes are limited by their sampling rate due to voltage sweeping processes, the multi-needle Langmuir probe (m-NLP) instrument has been developed to overcome this limitation, offering a higher sampling rate that is particularly advantageous for in-situ...
Narrowband (โf < 0.1 fcp), high-frequency (0.9 fcp < f < fcp) electromagnetic ion cyclotron (EMIC) waves, or HFEMIC waves for short, are a new type of EMIC waves found in the Earthโs inner magnetosphere. Observations suggest that they can be excited by low energy (< ~100 eV), very anisotropic protons. Here, we explore the instability threshold condition and hybrid simulations of HFEMIC waves,...
Mars lacks a global magnetic field but it has a weak induced magnetosphere resulting from the solar wind interaction with its upper atmosphere. Despite its slender spatial profile, it can facilitate various plasma wave activities. The Langmuir Probe and Waves (LPW) experiment aboard the MAVEN (Mars And Volatile EvoluioN) spacecraft has observed electrostatic solitary structures in the Martian...
Jupiter possesses the most hazardous radiation belt in the solar system which is responsible of trapping ultra-relativistic protons (~ 100 GeV), electrons (~ 100 MeV) and heavy ions like $O^+$, $O^{++}$, $S^+$, $S^{++}$, $S^{+++}$ (~100 MeV). Depending on the energy of the charged particles and the strength of Jupiter's magnetic field, these particles are either lost or trapped as they enter...
Kinetic Alfvรฉn waves (KAWs) have long wavelengths parallel to magnetic field lines and perpendicular wavelengths comparable to the ion Larmor radius. KAWs possess a parallel electric field component ($\delta E_{\parallel}$) that accelerates electrons along magnetic field lines [e.g., Hasegawa, 1976]. These waves are frequently observed in the terrestrial magnetosphere during substorms [e.g.,...
