טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYoav Hadas
SubjectPlasma Characterization of Pulsed High-Power Diodes
DepartmentDepartment of Physics
Supervisors Full Professor Krasik Yakov
Dr. Itzik Schnitzer
Professor Emeritus Felsteiner Joshua
Full Thesis textFull thesis text - English Version


Abstract

High power pulsed diodes are being used for a variety of applications such as high power lasers, relativistic high-power microwave tubes, x-ray sources, material processing and others. The key element in high-power diodes is the cathode suitable for generation of a high-current electron beam. The latter determines the efficiency of laser pumping, microwave tubes operation and other technological processes.  

High-Power Microwave (HPM) sources are a class of diodes in which the energy exchange is between the relativistic electron beam and the radiation field. The pursuit for hundreds of megawatts radiation levels had encouraged researchers to shift toward the relativistic devices where generation of >108 W pulsed electron beams can be achieved.

The purpose of this research was to investigate the parameters of the plasma during the operation of relativistic magnetron in order to characterize the plasma role in the microwave generation mechanism and try to suggest an improvement in the operation of the relativistic magnetron. The plasma expansion dynamics, the electrons temperature and density as well as the ions temperature were measured with space- and time-resolved diagnostics. The time and space evolution of these parameters and the correlation to the microwave pulse parameters were the basis for implementing a novel cathode to the relativistic magnetron. This ferroelectric plasma source cathode is characterized by plasma formation in an additional different process prior to the operation of the relativistic magnetron. The aim was to intentionally create the plasma in the interaction space of the magnetron before the high-voltage pulse of the magnetron is being supplied. This plasma will then be the source for the electrons needed for radiation generation. 

In the case of relativistic vircator operation, the electron beam is generated in the planar diode with the explosive emission plasma cathode. The investigation of a diode consisting of two ”stages” was motivated by the need to explore the mechanism of high-power electron beam generation by the dielectric multi-capillary cathode which showed low-electric field threshold of the plasma formation. This cathode was designed to have an igniter made of velvet. An application of the high-voltage pulse to the velvet igniter leads to the formation of the surface plasma. The latter serves as a source of primary electrons injected into the multi-capillary dielectric structure. The investigation of this cathode operation including characterization of the plasma inside the channels and at the dielectric surface was the basis for the cathode research for the relativistic vircator.