イオンエンジンにおけるビーム中和電子の粒子解析 (イオン加速グリッド耐久認定用数値解析 JIEDI(JAXA Ion Engine Development Initiatives) ツールの研究開発ワークショップ論文集)
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概要
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In order to examine the density and temperature distribution of electrons which neutralize ion beam emitted from an ion engine, we performed three-dimensional Particle-In-Cell simulations and investigated the electron behavior inside or outside the ion beam flows in the downstream region with respect to the accel grid. We calculated the charge density distribution of ions in three-dimensional spatial grid space covering the downstream region of the ion engine by using the ion beamlet data provided by Dr. Nakano. By solving Poisson's equation with the charge density data the potential distribution is calculated. Then we start emitting electrons from the down stream edge of the simulation region. At each time step, the charge density at each grid point is updated by the emitted electrons and the corresponding electric potential is renewed. By using the new potential values, we update the electrons dynamics by solving equation of motion for each electron. Since we focus on the short time scale of electron motion, we assume that ions which are about 100 thousand times heavier than electrons are immobile. We keep solving the above-mentioned PIC simulation until the steady state in terms of electron distribution is achieved. By using the electron data obtained in the simulations, we analyze the electron local temperature by calculating the local electron velocity distributions. From the data, we found that temperature is not uniform in space. The electron temperature at the ion beam edges become approximately 1.6 times higher than that of originally injected electrons