Particle-in-Cell Simulation of Langmuir Solitons’ Generation Mechanism - Towards Space Weather Forecast

• Main Authors: Shu-HaoChang, 張書豪
• Other Authors: Yasutaro Nishimura
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/q467e9

碩士 === 國立成功大學 === 太空與電漿科學研究所 === 104 === Space weather forecast is crucial to avoid the damage on the earth. In this work, the generation mechanism of Langmuir solitons is investigated. Langmuir solitons can be generated by solar bursts induced type III emission (Goldman, 1984) which is closely related to Langmuir turbulence giving precursor signals by radio wave reaching the earth. The behavior of Langmuir soliton generation mechanism is investigated by Particle-in-Cell simulation. As a preliminary study, linear and nonlinear Landau damping are benchmarked with a paper by C. Z. Cheng and G. Knorr (Cheng, 1976). The evolution of Non-Gaussian distributions with high-energy components as the generation mechanism of Langmuir soliton is studied. The bump-on-tail instability which provides us with the base of oscillating two stream instabilities (OTSI) is resumed. During the Langmuir solitons generation the spectrum of wave vectors (k-spectrum) is studied in detail. For the initial condition, Analytical solution of Zakharov equations and nonlinear Schrödinger (NLS) equation is employed, first. To employ the ion density and the electric field for soliton profiles, the electron density is obtained by inverting Gauss’s law. Furthermore, the solitons by external Radio-Frequency (RF) electric field (Valeo, 1974) are generated. Onset of oscillating two stream instability is observed after the collapse of solitons. The saturation mechanism of OTSI is discussed and understood as flattening of the distribution function by carefully looking into phase space dynamics.