| In this work, the limiting currents associated with charged particle beam transport are investigated for several different scenarios using various numerical techniques. The topic of limiting currents are of interest for essentially all applications that utilize charged particle beam formation and transport such as high-power microwave and x-ray generation, field-emitter-arrays in connection with vacuum microelectronics, semiconductor diodes, and ion acceleration, to name a few.;In the first part of this dissertation, the limiting currents of charged particle beams drifting through hollow grounded conductors along applied magnetic fields is investigated. A self-consistent limiting current theory originally developed for solid beams in vacuum is extended to a scenario which allows for annular beams in the presence of a dielectric load. This extension to the limiting current theory is followed by an analysis of it's validity by comparison to PIC simulations. It is found that when considering annular beams in the presence of a dielectric load, this expression is more accurate than more commonly used expressions. Following this, a mechanism which can enhance the limiting currents of a particle beam in a hollow drift-tube is investigated for solid and annular beams with and without a dielectric load present. This mechanism involves using the ponderomotive energy of an externally applied waveguide mode to thwart the beam space charge potential depression. It is found that for reasonable values of the electric field strength, the limiting current can be enhanced.;Following the work done with particle beams drifting through hollow cylindrical structures, the second part of this dissertation investigates limiting currents associated with coaxial cylindrical structures. An approximation is developed which describes the limiting currents of a finite-width annular beam drifting through a coaxial structure when an external voltage is applied to the inner conductor. This external voltage introduces an additional source of electrostatic energy into the system which in turn acts to thwart the detrimental beam space charge potential depression. Following this, the limiting currents are numerically calculated and studied when both a dielectric load and an externally applied voltage is present. It is found that in certain cases limiting currents are significantly enhanced when reasonable parameters are assumed.;In the third part of this dissertation, the behavior of particle beams in diode regions is explored. To start with, the generation of non-uniform current densities in diode regions in the electrostatic regime is investigated. It is found that there are significant current density enhancements at the edges of the beam and that there is an increase in the expected current when the size of the beam is reduced. As expected, when the beam width is increased, the obtained current approaches that of what is expected from one-dimensional theory. Following this, a particle trajectory model is developed for a beam traversing a diode region. This model is based on the Hamiltonian which describes the behavior of charged particles in the presence of external fields. Of interest is how the behavior of particles interacting with the self generated magnetic field is altered and how the calculated current is affected. |
