| Carbon widely exists in its various forms in nature, including its elementary substance in the form of allotropes, such as diamond, graphite, fullerene (C60), carbon nanotubes and graphene. These carbon materials with unique microstructure possess many novel physical and chemical properties, and thus have very broad application prospects. Exploring new growth points of application and new synthesizes of these carbon materials has become a research hotspot. Diamond owns a high energy absorption efficiency and a combustion efficiency, has an excellent radiopacity, a large bandwidth of optical transmittance, and great ability to withstand high pressure owing to its dense structure, these make it a very potential alternative of target materials in the inertial confinement fusion. On the other hand, people are actively exploring new methods for synthesis of carbon materials, including physical compression method, solution reaction method, graphite hot steam method, plasma-assisted chemical vapor deposition method, as well as underwater discharge method. Wherein, the underwater discharge technology works in environment with a pressure above atmosphere, generating a plasma of high activity, high particle density, which provide very favorable conditions for the synthesis of carbon materials.This dissertation carries out a technical research on fabrication of hollow diamond microspheres, focusing on the application of diamond in inertial confinement fusion target ball manufacturing. At the same time, as a preparatory work for synthesis of carbon materials by underwater discharge, a study of the generation and characteristics of underwater plasma is developed.DC plasma-enhanced chemical vapor deposition technology is applied for the fabrication of diamond target ball in the experiment. The discharge is operated under a pressure of about103Pa with methane and hydrogen as working gas. Diamond coating more than100micrometers in thickness is deposited on the surfaces of molybdenum and silicon balls which are2mm in diameter and driven by a rotatable anode base. Thereafter, opening on the coating is accessed through a100micron laser beam ablation, and self-supporting hollow diamond microspheres are obtained after corrosion of core ball via strong corrosive acid solution. Further, studies is done to prepare nanocrystalline diamond films with semiconductor properties, which is available by using mixing the working gas with borane.Gas-water interfacial plasmas under water were generated in a compact space in a tube with a sandglass-like structure, where a35KHz ac power source is applied. The dynamic behaviors of voltage/current were investigated for the powered electrode with/without water cover to understand the effect of the gas-water interface. It was found that the discharge exhibited periodic pulsed currents after breakdown as the powered electrode was covered with water, whereas the electrical current revealed a damped oscillation with time with a frequency about106Hz as the powered electrode was in a vapor bubble. By increasing water conductivity, a discharge current waveform transition from pulse to oscillation presented in the water covering case. These suggest that the gas-water interface has a significant influence on the discharge property.The discharge characteristics of high pressure (～100Torr) DC glow plasma are investigated by exploration the relationships between discharge current, voltage and pressure. By combining the evolvement process of the cathode glow, a self-regulatory function of the high-pressure plasma is found. Gas phase processes in a high pressure (～100Torr) DC hydrocarbon plasma were investigated in situ by optical emission spectroscopy and mass spectroscopy. In high pressure plasma, line emission characteristics of glow layers are obviously different. With increasing the pressure, electron excitation temperature decreases while gas rotational temperature goes up. High methane concentration caused an increase in C2, C2H2and C2H4but a reduction in C2H6. Those suggest that the effects from gas temperature on the gas phase processes are significantly enhanced under high pressure. |
