William Culbreth

Optimization of Chemical Etching Process in Niobium Cavities

Superconducting niobium cavities are important components of linear accelerators. Buffered chemical polishing (bcp) on the inner surface of the cavity is a standard procedure to improve its performance. The quality of bcp, however, has not been optimized well in terms of the uniformity of surface smoothness. A finite element computational fluid dynamics (cfd) model was developed to simulate the chemical etching process inside the cavity. The analysis confirmed the observation of other researchers that the sections closer to the axis of the cavity received more etching than other regions. A baffle was used by lanl personnel to direct the flow of the etching fluid toward the walls of the cavity. A new baffle design was tined using optimization techniques. The redesigned baffle significantly improves the performance of the etching process. To verify these results an experimental setup for flow visualization was created. The setup consists of a high speed, high resolution ccd camera. The camera is positioned by a computer-controlled traversing mechanism. A dye injecting arrangement is used for tracking the fluid path. Experimental results are in general agreement with computational findings.

PPPS-2013: Pulsed spherical reactor dynamics in a fissionable gas

Summary form only given. Pulsed gaseous fission reactors can be used to provide a transient source of neutrons for research or for power production. A mixture of gaseous, enriched UF6 and He may serve as the fuel and moderator for this design1. By using an external source of energy to produce a shockwave in this gaseous fuel, high density fluid produced by the shockwave can sustain criticality for a brief period of time. When the gaseous fuel is quiescent, the reactor remains subcritical.

PPPS-2013: Simulation of a gas puff injection system for a Dense Plasma Focus accelerator

Dense Plasma Focus (DPF) devices designed for the production of neutrons rely upon the rapid discharge of a capacitor bank through deuterium or tritium gas. Developed by J. Mather and N. Filippov in the 1960s1, these accelerators rely upon the electrical discharge to produce a current sheath that is rapidly accelerated by Lorentz forces as it travels along the anode of the device. This results in a radial collision of ionized gas at a pinched zone between the end of the anode and the cathode with sufficient velocity to induce fusion. A DPF accelerator can serve as a pulsed source of energetic neutrons with production rates of up to 1012 neutrons of 2.45 neutrons from D-D interactions or 1015 neutrons for D-T fusion in each pulse.

Status of the Nevada shocker at the University of Nevada Las Vegas

The Nevada shocker is a 540 kV, 7 /spl Omega/, 50 ns pulsed power device based on Marx bank and Blumlein technologies. The Marx bank is composed of nine 60 kV capacitors charged in series with a gamma high voltage source connected by means of Ross relays in an air environment. A trigatron switch energized with an isolated mini capacitor bank is used to erect the Marx bank. The trigatron switch and erecting electrodes are contained in a gas manifold pressurized to 20 /spl plusmn/ 1 psi with dry air. The energy is released sequentially through an inductor and a water filled charging transmission line to the Blumlein immersed in deionized water. The Blumlein shapes and compresses the energy into a 50 ns pulse upon discharge. A self-breaking water switch initiates the release of energy in the Blumlein. The energy flows through a water filled discharging transmission line to the diode end of the Nevada Shocker. The current diode end of the Blumlein supports vacuum pressures as low as 6.5 /spl times/ 10/sup -6/ Torr. The chamber is pumped with the aid of a roughing pump and a cryogenic vacuum pump. The vacuum section of the Nevada Shocker is currently being rebuilt to incorporate mechanical and thermal loading capabilities with sensors located at the experiment. A number of diagnostic developments are currently underway to support flashover studies on plastics. Resistive probe and differential B-dot diagnostics with the aid of a 6 GHz 20 GS/s TDS 6604 real time scope is documented demonstrating the capability of the machine.

Computer modeling of superimposed inviscid flows on a microcomputer

Complex flow patterns can be simulated in inviscid flow theory through the superposition of simple flows such as sinks, sources, and uniform flow. The resulting flows are valuable in modeling the flow of fluids at high Reynolds numbers and may be used to simulate the flow over airfoils, aircraft fuselages, ship hulls, and circular pipes in heat exchangers. A computer simulation program has been developed that models inviscid flow patterns and plots the resulting streamlines and equipotential lines on a microcomputer monitor. The program allows the user to superimpose doublets, sinks, sources, uniform flow, and vortices in any desired pattern. The code can also calculate and plot the inviscid velocity and pressure distribution at any point in the flow. A wide choice of singular 2-D flows can be superimposed with user-specified strengths, positions, and orientation angles. The program has been successfully used in undergraduate and graduate fluid mechanics courses and has been used to develop the pressure distributions around submerged structures.