Theory and mitigation of electron back-bombardment in thermionic cathode radio frequency guns

Includes bibliographical references.2015 Summer.Photocathode RF guns are currently the standard for high- power, low-emittance beam generation in free-electron lasers. These devices require the use of high-power lasers (which are bulky and expensive to operate) and high-quantum-efficiency cathodes (which have limited lifetimes requiring frequent replacement). The use of RF-gated thermionic cathodes enables operation without a large drive laser and with long lifetimes. One major limitation of RF-gated thermionic cathodes is that electrons emitted late in the RF period will not gain enough energy to exit the gun before being accelerated back towards the cathode by the change in sign of the RF field. These electrons deposit their kinetic energy on the cathode surface in the form of heat, limiting the ability to control the output current from the cathode. This dissertation is aimed at understanding the fundamental design factors that drive the back-bombardment process and at exploring novel techniques to reduce its impact on a high-current system. This begins with the development of analytic models that predict the back-bombardment process in single-cell guns. These models are compared with simulation and with a measurement taken at a specific facility. This is followed by the development of analytic models that predict the effects of space-charge on back-bombardment. These models are compared with simulations. This is followed by an analysis of how the addition of multiple cells will impact the back-bombardment process. Finally, a two-frequency gun is studied for its ability to mitigate the back-bombardment process. This dissertation provides new insight on how the back-bombardment process scales as a function of the beam parameters and how space-charge affects this process. Additionally this dissertation shows how a second frequency can be used to mitigate the back-bombardment effect

Design and simulation of the Colorado State University linear accelerator system

2014 Fall.Includes bibliographical references.The University of Twente in the Netherlands recently donated a linear accelerator and free-electron laser system to Colorado State University. A detailed model and simulation of the system must be constructed in order to assist the re-commissioning process at CSU. An initial design of the beam-transport system must also be developed. This thesis begins with the basic theory needed to understand the context of the simulations and then works through the accelerator, starting from the point where the beam is generated and continuing through the whole system to the beam dump. Individual components are simulated, their parameters are characterized, and optimal initial settings are found. These individual simulations are then combined into a complete start-to-end simulation of the machine. The start-to-end simulation is then used to demonstrate the expected performance of the machine with the optimal settings. This provides a system design that will be used in the initial buildup of the accelerator, as well as a simulation tool that can be used for future studies (for example, testing of novel components) or for examining the impact of proposed design changes

Compact ring-based X-ray source with on-orbit and on-energy laser-plasma injection

We report here the results of a one week long investigation into the conceptual design of an X-ray source based on a compact ring with on-orbit and on-energy laser-plasma accelerator. We performed these studies during the June 2016 USPAS class "Physics of Accelerators, Lasers, and Plasma..." applying the art of inventiveness TRIZ. We describe three versions of the light source with the constraints of the electron beam with energy $1\,\rm{GeV}$ or $3\,\rm{GeV}$ and a magnetic lattice design being normal conducting (only for the $1\,\rm{GeV}$ beam) or superconducting (for either beam). The electron beam recirculates in the ring, to increase the effective photon flux. We describe the design choices, present relevant parameters, and describe insights into such machines.Comment: 4 pages, 1 figure, Conference Proceedings of NAPAC 201

How Active is Your Fund Manager? A New Measure That Predicts Performance

Abstract We introduce a new measure of active portfolio management, Active Share, which represents the share of portfolio holdings that di¤er from the benchmark index holdings. We compute Active Share for domestic equity mutual funds from 1980 to 2003. We relate Active Share to fund characteristics such as size, expenses, and turnover in the cross-section, and we also examine its evolution over time. Active Share predicts fund performance: funds with the highest Active Share signi…cantly outperform their benchmarks, both before and after expenses, and they exhibit strong performance persistence. Non-index funds with the lowest Active Share underperform their benchmarks. JEL classi…cation: G10, G14, G20, G2

Comparison of out-of-range values and frequency of adverse events among HIV infected pregnant/postpartum women in the Kisumu Breastfeeding Study (KiBS) obtained from using locally-established reference intervals for pregnant and non-pregnant women in Kenya, United States reference intervals and DAIDS toxicity tables.

<p>2012–2015.</p