|M.Sc Student||Raanan Gad|
|Subject||Investigation of a Hollow Anode with an Incorporated|
Ferroelectric Plasma Source in Millisecond Time
|Department||Department of Physics||Supervisors||Full Professor Krasik Yakov|
|Professor Emeritus Felsteiner Joshua|
|Full Thesis text|
A great importance with many applications is accounted for intense pulsed and dc electron and ion sources. Previous investigations showed that a Hollow Anode (HA) with a ferroelectric plasma source (FPS) incorporated in it, can be used as an effective electron source for generation of electron beams with current densities ~ 102 A/cm2 in sub-microsecond time scale. The main objective of this research was to investigate the capability of the FPS-assisted HA to operate in a millisecond time scale, which is a major milestone in proving the feasibility of dc operation.
Time and space resolved characterization of the main plasma parameters (density, temperature, flow velocity and uniformity) generated by FPS-assisted HA, using various plasma diagnostic techniques (such as visible light spectroscopy and electrical probes), was carried out.
A millisecond time scale operation of the HA with incorporated FPS was demonstrated at background pressure of 10-5-10-4 Torr and charging voltage in the range of 1 - 2 kV. HA discharge current density of ~ 10 A/cm2, and plasma density in the range of 1013 - 1011 cm-3 during the entire HA discharge were measured. It was shown that the HA plasma consists of ions originating from the FPS material as well as background gas. An almost constant ion temperature (< 1 eV) and an electron temperature in the range of 5 - 15 eV were obtained. It was shown that the plasma electron density gained a maximum value of ~ 1014 cm-3 at ~ 2 mm in front of the FPS surface. This plasma is considered to sustain the long-lived operation of the HA high-current discharge. It was found that during the HA discharge, the electron energy distribution function is characterized by Maxwellian distributed electrons and fast non-Maxwellian electrons, with energy of ~ 100 eV. It was shown that there is a periodical strata-like structure of the plasma density which could be associated with an instability induced by overheated plasma. Also it was found that the longitudinal plasma expansion velocity is significantly larger than the thermal plasma expansion velocity. Finally, the long term characteristics of the FPS-assisted HA were clarified and its operation in millisecond time scale was accomplished.