No less than 99.9% of visible matter in our universe is in the collisionless plasm state. Hence, it is essential for understanding of our universe to study collisionless space plasma. This paper introduces various basic theories with different approximations for space plasma. Various numerical methods for simulating space plasma with these basic equations are also described briefly.
Numerical simulations of plasma processes taking place near spacecraft require fully-kinetic modeling of plasmas, proper particle and field conditions at spacecraft surfaces, and sound parallelization strategy adapted for modern supercomputers. Some relevant techniques are presented, with particular focus on the use of the particle-in-cell approach, charge redistribution processed on conducting surfaces, and a robust load balancing algorithm for distributed-memory parallel computers. Example applications to emerging spacecraft-plasma interaction problems are presented, on spacecraft charging processes in non-stationary space environments as well as electron acceleration processes within microwave discharge chambers designed for ion thrusters.
Auroral breakup is the term used to describe a transient phenomenon in which brightness of aurora suddenly increases and the bright aurora expands rapidly. When the auroral breakup takes place, the magnetosphere and the ionosphere are highly disturbed. The ultimate cause of the auroral breakup is the Sun, but intermediate processes between them remained unsettled. The global magnetohydrodynamics (MHD) simulation developed by Prof. Emer. Takashi Tanaka is shown to reproduce well the sequence of the auroral breakup. Here, we show the intermediate processes leading to the auroral breakup on the basis of the results obtained by the MHD simulation.
Space plasmas are essentially collisionless. Kinetic energies of plasmas are transferred through wave-particle interactions. Since plasmas are dispersive media, plasma waves show various features depending on how and which plasma wave modes interact with particles. Plasma wave observations via scientific satellites have a key role in knowing physical processes in space. Plasma wave investigation systems on board satellites are dedicated to the observations of electric field and magnetic field components of plasma waves. They consist of sensors, receivers and an onboard digital processing unit. While dipole antennas are used for electric field sensors, search coil magnetometers or loop antennas are used for magnetic field sensors. Plasma wave receivers are a kind of sophisticated radio receivers. The recent plasma wave receiver is designed as a waveform receiver that can save its mass and size. In addition to waveforms, the waveform receiver provides frequency spectra which are calculated in the digital processing unit from the observed waveforms. The present paper introduces plasma wave observation by scientific satellites on the basis of the latest design of plasma wave investigation systems.
In many fluid-structure-interaction problems, the “added mass,” “inertial mass,” “virtual mass,” “carried mass” or “induced mass” is one of important interests. In the present study, the authors focus on the fluid force of an oscillating sphere in stationary incompressible-and-viscous fluid. More specifically, the authors conduct experiments in order to reveal the fluid force, comparing the experiments with the linear theory assuming an infinitesimal oscillation amplitude. As a result, the experiments show good agreement with the linear theory. This confirms the accuracy of the experiments, together with the effective amplitude’s range where the linear theory is valid.