Numerical studies on ultrarelativistic ion motions in an oblique magnetosonic shock wave

The motion of ultrarelativistic ions in an oblique magnetosonic shock wave is studied analytically and numerically. The zeroth-order theory predicts that an oblique shock wave can accelerate ions in the direction nearly parallel to the magnetic field if the shock speed is vsh ? c?cos?θ, where θ is the angle between the wave normal and the magnetic field, while the perturbation is a one-dimensional oscillation nearly perpendicular to the zeroth-order motion. The perturbation frequency ω is of the order of Ωi0γ?1/2, where γ is the Lorentz factor of the zeroth-order velocity. These theoretical predictions are examined with test particle simulations, in which the test particle orbits are calculated with use of the electromagnetic fields of a shock wave obtained from an electromagnetic particle simulation. The zeroth-order and perturbed motions in the simulations are explained by the theory

Development of Multi-Hierarchy Simulation Model with Non-Uniform Space Grids for Collisionless Driven Reconnection

A multi-hierarchy simulation model aimed at magnetic reconnection studies has been developed, in which macroscopic and microscopic physics are solved self-consistently and simultaneously. In this work, the previous multi-hierarchy model by these authors is extended to a more realistic one with non-uniform space grids. Based on the domain decomposition method, the multi-hierarchy model consists of three parts: a magnetohydrodynamics algorithm to express the macroscopic global dynamics, a particle-in-cell algorithm to describe the microscopic kinetic physics, and an interface algorithm to interlock macro and micro hierarchies. For its verification, plasma flow injection is simulated in this multi-hierarchy model and it is confirmed that the interlocking method can describe the correct physics. Furthermore, this model is applied to collisionless driven reconnection in an open system. Magnetic reconnection is found to occur in a micro hierarchy by injecting plasma from a macro hierarchy

Pseudo-Maxwellian Velocity Distribution Formed by the Pickup-like Process in Magnetic Reconnection

Focusing on ring-shaped ion velocity distributions with a finite width formed in magnetic reconnection in the presence of a guide magnetic field, intriguing roperties such as the formation mechanism, a significant change in the shape, and necessary conditions for the change are investigated by means of theory and simulations. The width of a ring velocity distribution predominantly riginates from velocity variations of seed particles for the pickup-like process. A function exactly representing a ring with a width is analytically formulated, assuming a steady supply of seed particles satisfying a Maxwellian velocity distribution and a mixing of gyration phases. The formulated function indicates that when the ring width is larger than a criterion, the local minimum of the ring’s center is changed into the maximum, and the shape is transformed into a mountain shape. Such a mountain-like distribution is defined as “a pseudo-Maxwellian distribution,” because it is almost indistinguishable in shape from a genuine Maxwellian distribution. Actually, particle simulations demonstrate that mountain-shaped ion velocity distributions are formed during magnetic reconnection with a guide magnetic field, and it is nearly concluded that they are pseudo-Maxwellian distributions. Moreover, two types of evidence for pseudo-Maxwellian distributions are shown by simulations. One is to analyze the dependence of the distribution shape on the guide magnetic field, which is explored by the particle simulation. In cases of slightly different values of the guide field, vague shapes of rings with a width are observed as ion velocity distributions. The other is to observe velocity distributions under a hypothetical condition of an artificial zero temperature in the upstream by utilizing a test particle simulation. In the test particle simulation, ring-shaped distributions with a width are clearly seen, because the velocity variations in the upstream are reduced. From the two types of evidence, it is definitely confirmed that the mountain-shaped distributions found in the particle simulations are pseudo-Maxwellian distribution. These results imply that pseudo-Maxwellian distributions would be created for various cases of guide field magnetic reconnection

Effective heating of nonadiabatic protons in magnetic reconnection with a guide field

The mechanism of plasma heating through magnetic reconnection with a guide magnetic field is investigated by means of two-dimensional electromagnetic particle simulations. These simulations mimic the dynamics of two torus plasmas merging through magnetic reconnection in a spherical tokamak (ST) device. It is found that a large part of protons, which behave as nonadiabatic, are effectively heated in the downstream because a ring-like structure of proton velocity distribution is observed at a local point in the downstream. The characteristic features of the velocity distribution can be explained as the following proton motion. Upon entering the downstream across the separatrix, nonadiabatic protons suddenly feel the strong electromagnetic field in the downstream and move in the outflow direction while rotating mainly around the guide magnetic field. The protons gain kinetic energy not only on the separatrix but also in the downstream. This effective heating process can be interpreted as the “pickup,” which, however, was thought to be responsible for only heavy ions. In this work, it is demonstrated that the pickup of protons is compatible with the known pickup theory in the cases in which the plasma beta is much less than 1, which is satisfied in STs

Dependence of the Pickup-Like Ion Effective Heating on the Poloidal and Toroidal Magnetic Fields during Magnetic Reconnection

The dependence of the ion effective heating on the poloidal (reconnection) and toroidal (guide) magnetic fields during magnetic reconnection in the presence of a guide magnetic field is investigated by means of particle simulations, which mimic merging plasmas in a spherical tokamak. In previous works, our simulations demonstrated that the ion temperature perpendicular to the magnetic field grows mainly in the downstream, in which ring-shaped velocity distributions are formed. This means that ions are effectively heated. The basic theory explains that the ring-shaped distribution is formed by the ions which rotate around the guide magnetic field while E × B drifting. In this work, the basic theory is extended to a more general theory including not only a ring-shaped distribution, but also a circular-arc-shaped distribution. The generalized theory explains that the effective temperature changes by the radius and the central angle of the arc-shaped velocity distribution and conjectures the dependence of the ion effective heating on the poloidal and toroidal magnetic fields. The simulations show that the ion heating energy is proportional to the square of the poloidal magnetic field, whereas the ion temperature decreases as the toroidal field is larger, but the toroidal field dependence becomes small for the regime of high toroidal field. These tendencies are consistent with those observed in experiments

心臓手術をうけた患者血清と心嚢水におけるマイクロRNA423-5pの発現様式

京都大学0048新制・課程博士博士(医学)甲第19572号医博第4079号新制||医||1013(附属図書館)32608京都大学大学院医学研究科医学専攻(主査)教授 萩原 正敏, 教授 小西 靖彦, 教授 齊藤 博英学位規則第4条第1項該当Doctor of Medical ScienceKyoto UniversityDFA