|Ph.D Student||Yarmolich Dmitry|
|Subject||Experimental and Theotetical Research of Passive and|
Active Pulsed Plasma Cathodes
|Department||Department of Physics||Supervisor||Professor Yakov Krasik|
|Full Thesis text|
The purpose of the research was the investigation of passive and active plasma cathodes. Here by passive cathodes we assume cathodes which produce plasma during the accelerating pulse and active cathode are characterized by plasma generation prior to the application of the accelerating pulse. As a passive cathode a novel type of plasma source was suggested and investigated for reliable and reproducible generation of high-current electron beam (~1.5 kA, ~30 A/cm2, ~300 ns) in a diode powered by a high-voltage pulsed generator (~200 keV, 78 W). The cathode operation is based on formation of plasma sheets inside the dielectric slots due to intense surface discharge. The plasma density ≤1015cm3 was measured using Stark broadening of Hα and Hβ lines. The plasma temperature of ~7eV was obtained. A model of the plasma inside the micron width slot was developed. The model allows one to estimate the dependence of the plasma parameters on the current and neutral densities as well as the slot width for extraction of an electron beam with the required parameters. Two types of active plasma cathodes were investigated, namely the ferroelectric plasma source (FPS) and the hollow plasma anode. The research of FPS showed that the plasma formation is accompanied by emission of charged micro-particles, fast neutrals, and extreme ultra-violet radiation. The investigation of fast neutrals emission revealed that the neutral velocity 7∙107cm/s and that this emission occurs in 2π solid angle. It was found that micro-particles have an average size of ~5 µm, density of ~7∙104 cm−3, positive charge of ~6∙10−15 C, and velocity of ~6∙103 cm/ s in the case of a 12 kV amplitude driving pulse. These data allowed us to suggest a concept of a FPS based thruster. The thrust was measured for driving pulse of a 4.5 kV and a repetition rate of 1 kHz. Time- and space- resolved spectroscopy and Thomson scattering diagnostics of the plasma in the hollow anode (HA) with incorporated FPS were performed. These measurements have demonstrated that during the HA operation the density and energy of the ferroelectric surface plasma electrons are ~1015 cm-3 and ≤ 5 eV, respectively. The density and temperature of the bulk HA plasma electrons were found to be ~6´1013 cm-3 and ~10 eV, respectively. During the accelerating pulse, the surface plasma electron density and energy are increased up to ~6×1016 cm-3 and ≤20 eV, respectively, while the bulk plasma parameters remain unchanged.