The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Summary form only given. The THz spectrum is rapidly growing in importance for a variety of applications including molecular spectroscopy and high-data-rate communications that require efficient, tunable high-power sources with high spectral purity. Conventional THz backward wave oscillators (BWO), such as those available from ISTOK, offer both frequency stability and tunability. Herein, we report...
Summary form only given. Simulations of dense kinetic plasmas are an area of active research. A variety of devices from high power microwave devices to Hall thrusters involve situations with dense fluidlike plasmas coexisting with important kinetic non- Maxwellian particle distributions. These plasmas exhibit a range of length and time scales, making accurate simulation a challenging and computationally...
Summary form only given: The effect of ions in a magnetically insulated crossed-field gap is studied using a particle-in-cell simulation with Monte Carlo collisions (MCC). (Code available through the PTSG at UC Berkeley.) These results are compared with the predictions from single particle orbit, shear flow models and previous particle-in-cell simulations in which the ions were modeled as a sheet...
Summary form only given. Pulse detonation engines offer the potential for a single, air- breathing, propulsion system that can operate from subsonic speeds (including take-off) to high Mach number flight. Critical to this technology is rapid repetition rate operation. Plasma-based ignition systems based on short pulse, high voltage pulsed power have been shown to decrease the ignition time in experimental...
From a circuit model for an oscillator, an equation was developed to describe the beam loaded admittance. The equation, which is presented in this paper suggests that the instantaneous beam loaded admittance, may be extracted from the output signal of the oscillator once the cold tube frequency and damping rates have been determined. This technique is used to analyze the behavior of a relativistic...
Summary form only given.Nonlinear transmission lines have been demonstrated to be an effective technique for generating high power ultrawideband or mesoband radiation without the need for a vacuum system, electron beam, or magnet. Preliminary experiments have been performed at AFRL and UM on a discrete element nonlinear transmission line with nonlinear capacitance. Depending on the injected pulse,...
We evaluate the effects of small random fabrication errors on the small signal characteristics of a traveling wave tube.The classical ID small signal theory of Pierce, is applied. Random, axially varying perturbations are introduced in the circuit phase velocity mismatch the gain parameter and cold tube circuit loss in Pierce notation. First order perturbation analysis of the small signal equations...
This paper reports on the development of a heuristic renormalization method that rescales the bare electron charge assuming the existence of a screening cloud of dense plasma in a manner identical to the formation of the Debye sheath. This renormalization is used to provide an interpretation of the standard particle-in-cell (PIC) weighting of particle information to the grid. This provides a natural...
Summary form only given. pulse detonation engines (PDE) are a class of air breathing engines that offer propulsion from sub- to supersonic velocities from a single system. Critical to this technology is the robust and reliable operation at high repetition rates. This forces consideration of a variety of science and engineering challenges to develop systems that rapidly detonate the fuel-air mixture...
Summary form only given. Phase-locking is utilized today in many important applications, ranging from small scale devices such as cardiac pacemakers to large scale devices such as radar. We have adopted a magnetron-specific model to qualitatively explain the various regimes observed in magnetron injection-locking experiments, which utilize two continuous wave magnetrons; one functions as an oscillator...
We seek to understand the transient behavior that is occasionally observed in field emitter experiments, as well as the relationship between the Fowler-Nordheim parameters deduced from pulsed and steady-state experiments. To this end, a model is constructed to study the effects of the gap capacitance and the base resistance on the evolution of the emitted current from a field emitter that is subjected...
Motivated by current interest in sub-mm and THz slow wave vacuum electronic amplifiers, which employ miniature, difficult-to-manufacture slow wave circuits, we evaluate the effects of small random fabrication errors on the small signal characteristics of a TWT.
In this paper, effects of time-varying frequencies on the injection locking behavior are explored. Of interest is when the driver frequency is linearly swept (chirp) in time, e.g., for frequency search when the oscillator frequency is not known. It is found that complete locking similar to the constant frequency case can no longer occur. Instead, frequency of the oscillator "tracks" the...
Motivated by current interest in submillimeter and terahertz (THz) slow-wave vacuum electronic amplifiers, which employ miniature, difficult-to-manufacture slow-wave circuits, we evaluate the effects of small random fabrication errors on the small-signal characteristics of a traveling wave tube. The classical 1-D small-signal theory of Pierce, generalized to allow axially varying circuit characteristics,...
Summary form only given. Phase-locking is utilized today in many important applications, ranging from small scale devices such as cardiac pacemakers to large scale devices such as radar. We have recently developed a magnetron-specific model to qualitatively explain the various regimes observed in magnetron injection-locking experiments, which utilize two continuous wave magnetrons: one functions as...
Summary form only given. Motivated by the current interest in vacuum slow wave THz sources, where difficult-to-manufacture miniature slow wave circuits are required, we evaluate the effects of geometrical random errors introduced during the circuit manufacturing processes on the small signal gain and phase characteristics of a traveling wave tube amplifier. A continuum model is used. Random perturbations...
Summary form only given. The presence of plasma has long been suspected to be a major cause of gap closure in high power crossed-field diodes and HPM sources, even under the condition of magnetic insulation as in relativistic magnetrons. Our recent work [Lau et al., 2007] suggested that the presence of positive charge, anywhere in the diode gap, always increases the extent of the electron hub height...
This paper gives an overview of how RF systems, from pulsed power to antennas, may be virtually prototyped with the improved concurrent electromagnetic particle-in-cell (ICEPIC) code. ICEPIC simulates from first principles (Maxwell's equations and Lorenz's force law) the electrodynamics and charged particle dynamics of the RF-producing part of the system. Our simulations focus on gigawatt-class sources;...
Summary form only given. The state-of-the-art in first principles physics software has greatly advanced in the last few years though the advent of highly efficient, scalable parallel software and ubiquitous Beowulf-class clusters. In the arena of high power microwave and X-ray sources, it is not unusual to simulate multi-dimensional (2- and 3-D), fully electromagnetic situations with fidelity sufficient...
Summary form only given. A calculation of the loading of a resonant cavity by an electron beam is presented. This calculation is the first to include all effects of AC space charge. The fields in the cavity are determined in the presence of the beam, including the effects of higher order structure modes. The formulation extends Wessel-Berg's classic treatment of AC space charge effects, explicitly...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.