イオン音波の非線形現象 : ソリトンからカオスへの遷移およびシース構造の分岐

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 吉田 善章, 東京大学教授 小川 雄一, 東京大学教授 鈴木 宏二郎, 東京大学准教授 西浦 正樹, 日本大学元教授 戸次 直明University of Tokyo(東京大学

Numerical approximation of the Euler-Poisson-Boltzmann model in the quasineutral limit

This paper analyzes various schemes for the Euler-Poisson-Boltzmann (EPB) model of plasma physics. This model consists of the pressureless gas dynamics equations coupled with the Poisson equation and where the Boltzmann relation relates the potential to the electron density. If the quasi-neutral assumption is made, the Poisson equation is replaced by the constraint of zero local charge and the model reduces to the Isothermal Compressible Euler (ICE) model. We compare a numerical strategy based on the EPB model to a strategy using a reformulation (called REPB formulation). The REPB scheme captures the quasi-neutral limit more accurately

Ion Acceleration by Solitary and Shock Waves Driven by Laser- Plasma Interactions

This thesis presents a theoretical study of the interaction of intense, ultrashort laser pulses with overdense plasmas. Main objectives are to understand the basic phenomenon which leads to the formation of non-linear electrostatic coherent wave structures in form of either solitary ion acoustic waves (SAW) or collisionless shock waves (CSW). These different types of waves have been classified according to Sagdeev’s theory and related formulas have been used for comparison with the numerical results. The particular focus is on the effect on ion acceleration, by means of ion refection by the moving electrostatic field associated to the shocks/solitons. An extensive numerical study by 1D PIC simulations has been performed and in particular the differences arising between linearly polarized pulses and circularly polarized pulses have been discussed. In a cold plasma, ion bunches produced by “hole boring” (HB) radiation pressure acceleration at the target surface may propagate in the bulk as solitary waves. The acceleration mechanism of these ion bunches has been discussed pointing out a distinction between shock acceleration (SA) and HB acceleration, also with respect to some recent experimental results. Stability of (SAW) or (CSW) and ion reflection from them has been found to be strongly dependent on the initial velocity distribution of ions. The effect of both the ion and the electron temperature on the generation and evolution of solitary acoustic waves have been discussed

NIAC Phase I Final Report: On-Orbit, Collision-Free Mapping of Small Orbital Debris

Sub-centimeter orbital debris is currently undetectable using ground-based radar and optical methods. However, the pits in Space Shuttle windows produced by paint chips (e.g. the 3.8mm diameter pit produced by a 0.2mm paint chip on STS-7) demonstrate that small debris can cause serious damage to spacecraft. Recent analytical, computational and experimental work has shown that charged objects moving quickly through a plasma will cause the formation of solitons in the plasma density. Due to their exposure to the solar wind plasma environment, even the smallest space debris will be charged. Depending on the debris size, charge and velocity, the plasma signature of the solitons may be detected by simple instrumentation on spacecraft. We will describe the amplitude and velocity of solitons that may be produced by mm-cm scale orbital debris in LEO. We will discuss the feasibility of mapping sub-cm orbital debris using a fleet of CubeSats equipped with Langmuir probes. The time and fleet size required to map the debris will also be described. Plasma soliton detection would be the first collision-free method of mapping the small debris population

NEW SELF-GRAVITATIONAL OSCILLATORY EIGENMODE PATTERNS OF SOLAR PLASMA WITH BOLTZMANN-DISTRIBUTED ELECTRONS

We attempt to propose a simplified theoretical model to study new stationary states of the nonlinear self-gravitational fluctuation dynamics of the solar plasma with the zero-inertia electrons against weakly nonlinear perturbation within the framework of the Jeans homogenization assumption. This is based on a bi-fluidic approach with the thermal electrons treated as the Boltzmann-distributed species. The joint effects of space-charge polarization, sheath-formation, and bi-layer plasma-boundary interaction through gravito-electrostatic interplay in a spherically symmetric geometry are considered. Applying a standard multiscale technique, a unique form of extended Korteweg-de Vries-Burger (e-KdVB) equation with a new selfconsistent linear sink is methodologically developed. The origin of the unique sink lies in the spherically symmetric self-gravity contributed by the massive ions. A numerical shape-analysis with multi-parameter variation depicts the co-existence of two distinct classes of new eigenmode excitations. The fluctuation patterns evolve as oscillatory soliton-like and oscillatory shock-like patterns in judicious plasma conditions under the adiabatic electronic response. Their oscillations, arising due to resonant and non-resonant coupling phenomena with the background spectral components, get gradually damped out due to the sink. This scientific study allows us to conjecture that the model supports self-gravitational solitary (shock) waves having tails (fronts) composed of a sequence of slightly overlapping solitons with smoothly varying characteristic parameters. Our results are compared with the earlier theoretical model predictions, on-board multispace satellite data and spacecraft observations highlighting tentative future scopes