|Ph.D Student||Beilin Leonid|
|Subject||Nanosecond Timescale Plasma Formation in Pressurized Gases|
in the Presence of High-Intensity Electromagnetic
|Department||Department of Physics||Supervisor||Professor Yakov Krasik|
|Full Thesis text|
The subject of this research is investigation of the parameters of nanosecond timescale plasma formation in pressurized gases in the presence of high-intensity electromagnetic field. This electromagnetic field is produced in high-power microwave (HPM) pulse compressors attracting much attention due to potential applications for high-energy accelerators and radar systems. The HPM pulse compressors operation is based on microwave energy accumulation and its rapid release from a resonant cavity. The extraction of energy from a cavity is achieved using the key element in HPM compressors - a fast plasma interference switch. Presently, there is no clear understanding of processes governing plasma formation, its expansion under high-frequency electric field in pressurized gases, and the influence of the dynamically changing plasma parameters on the output microwave pulse. Thus, the main objectives of the present research were to conduct theoretical, numerical, and experimental studies of physical phenomena which accompany plasma formation during microwave energy release from HPM compressors with interference plasma switches.
Two types of such switches were considered. For the commonly used H-plane tee, first, fast-framing imaging of light emission from plasma was carried out. Using the imaging data, the typical size of plasma, velocity of its expansion along the electric field, and plasma density were estimated. In addition, to investigate plasma dynamics at the early stages of its formation, for the first time, the non-disturbing time-resolved optical emission spectroscopy was performed. From the spectroscopy measurements the nanosecond-scale plasma density evolution was obtained in correlation with the waveform and power of the microwave output pulse. An alternative plasma switch, considered in this work, was a Magic-tee. In contrast to H-tee based compressors operating in a single frequency, with a Magic-tee geometry adjustment for a frequency change is not required. The Magic-tee-based compressor output in two operating frequencies without mechanical tuning has been demonstrated for the first time in this work. In addition to experimental investigations, the numerical simulations of the plasma evolution and microwave energy release from the cavity were conducted. The simulations yield results in good agreement with measured output pulse peak power and waveform and the plasma density evolution.
The obtained experimental and simulation results of the plasma dynamics gave important insights for understanding the physical phenomena accompanying plasma formation and for practical applications of HPM compressors with plasma interference switches.