The aim of the thesis is to examine plasma-wall interaction using computer modeling. Tokamak- relevant plasma conditions are simulated using the particle-in-cell model family SPICE working in three or two dimensions. SPICE model was upgraded with a parallel Poisson equation solver and a heat equation solver module. Plasma simulation aimed at synthetic Langmuir probe measurements were performed. First set considered a flush-mounted probe and the effect of variable magnetic field angle was studied with aim to compare existing probe data evaluation techniques and assess their operational space, in which the plasma parameters estimation via fit to the current-voltage characteristic is accurate. Second simulation set studied a protruding probe pin. Effective collecting area of such probe was investigated with intentions of density measurement collection. This area was found to be influenced by a combination of two factors. First, the density dampening inside the magnetic pre-sheath of the probe head, and the second, the extension of the area caused by Larmor rotation. A comparison with experimental results obtained at COMPASS tokamak was was performed, confirming these results. Keywords Langmuir probe, simulation, particle-in-cell, tokamak, Poisson equation, COMPASS 1

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21069号 / 工博第4433号 / 新制||工||1689(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 山川 宏, 教授 松尾 哲司, 准教授 海老原 祐輔 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

Axisymmetric radial Bernstein modes are known to exist in non-neutral plasmas and have been studied theoretically and computationally in 1D, but detection of these modes has still proven to be difficult due to self-shielding. To help advance the work on this front we created a 2D particle-in-cell (PIC) code that simulates a non-neutral plasma in a Malmberg-Penning trap. A detailed description of the PIC code itself has been included that highlights the benefits of using an $r^2$--$z$ grid and how it can be tested. The focus of the PIC simulation was to discover how best to drive and detect these modes. While it is improbable that radial Bernstein modes will be detected in long plasmas, we show that it may be a possible due to the axial nodal structure in the potential and electric field generated by confining plasmas of any finite-length. Additionally, we find that for a short plasma the strongest detection signal along the trap wall occurs at the plasma's midpoint rather than near the ends. Results show that oscillating the confinement potentials is sufficient to excite the fundamental radial Bernstein mode, but not any of the higher order modes. The higher order modes can be seen in the simulation, however, by sinusoidally driving the radial electric field. Unfortunately, the individual modes are difficult to isolate which we suspect is due to mode mixing. Finally, we report frequencies and mode shapes for the fundamental mode and the (lower) first higher order mode.

No description available.

No description available.

No description available.

No description available.

No description available.

Stimulated electromagnetic emission (SEE) produced by interactions of high-power radio waves with the Earth's ionosphere is currently a topic of significant interest in ionospheric modification physics. SEE is believed to be produced by nonlinear wave-wave interactions involving the electromagnetic and electrostatic plasma waves in the altitude region where the pump wave frequency is near the upper hybrid resonance frequency. The most prominent upshifted feature in the SEE spectrum is the broad upshifted maximum (BUM). In this study, the instability processes thought to be responsible to the BUM spectra in the SEE experiments are discussed and analyzed using theoretical and electrostatic particle-in-cell (PIC) models. From characteristics of this feature, a four-wave parametric decay process has been studied as a viable mechanism for its production. The object is to (1) investigate the early time nonlinear development of the four-wave decay instability by using theoretical and numerical simulation models, (2) study the variation of the four-wave decay instability spectral features for a wide range of plasma and pump wave parameters, and (3) access its possible role in the production of the BUM spectral feature. Results of this investigation show that there is good agreement between predictions of the proposed theoretical model and the numerical simulation experiments. The simulation electric field power spectrum exhibits many of the important features of the experimental observations. The numerical simulation results show that consideration of the full nonlinear development of the four-wave parametric instability is crucial in providing insight into the asymmetric nature of the wave frequency spectrum observed during the experiments. The velocity-space ring-plasma instability, another generation mechanism for the BUM spectra, is studied using a theoretical model. The theoretical calculations show that the growth rate is larger in the region of the upper hybrid wave than that of the electron Bernstein wave. In addition, the effects of various plasma parameters are analyzed and it is predicted that the BUM should be more prominent with a hotter ring, at the direction perpendicular to the magnetic field, or in a closer region of cyclotron harmonic. A detailed comparison of the velocity space ring-plasma instability and the four-wave parametric process is presented where both the differences and the possible relations are discussed. / Ph. D.