Development of a RF Class E amplifier to power a ferroelectric plasma thruster [abstract]

Abstract only availableClass E amplifiers are a special class of electronic amplifiers which are highly efficient at delivering power at high frequencies. Class E amplifiers consist of a signal generator, switch, and two LC resonant circuits. The resonant circuits are tuned to a specific frequency, which requires the amplifier to be designed to a particular frequency. This amplifier is being developed to power the Ferroelectric Plasma Thruster (FEPT) which creates plasma when excited by a high voltage, high frequency signal. The FEPT has a piezoelectric resonance near 400 kHz, so an operating frequency of 375 kHz was selected for optimal performance. The goal of this project is to reduce the size and amount of equipment to operate the FEPT. Design goals require volume, weight, and electrical inputs to be kept to a minimum so that the amplifier and FEPT can be merged together into a small package

Linearity testing of LED transmitter and corresponding voltage to current op-amp configuration [abstract]

Abstract only availableThe LM7171 operational amplifier is made for high electrostatic discharge and fast signal performance. In a configuration using the diode in the transmitter and a resistor on the negative op-amp terminal, the op amp will convert the voltage measurement to a current value, which will then be sent linearly via the HFBR-1414MZ optical transmitter over optical fiber. First, the transmitter and receiver pair will be tested for linearity using a variable current source. Should data confirm linearity, the voltage to current op amp configuration will be tested. This paper presents the results of these tests. This project is sponsored by Los Alamos National Laboratory.Los Alamos National Laborator

Characterization of runtime and jitter on a megavolt laser triggered spark gap switch [abstract]

Abstract only availableLaser triggering has been utilitzed in spark gap switches to initiate switch breakdown resulting in more reliable and repeatable switching. Many studies have focused on how various parameters of the switch or the laser triggering system affect the timing of the breakdown in an attempt to minimize the jitter associated with the switch. In preparation for a future study characterizing runtime and jitter with respect to switch and laser parameters, an extensive literature review of laser triggered spark gap switches has been completed. The focus of the study has consisted mainly on large megavolt switches similar to the 1 MV, SF6 filled, laser triggered gas switch installed at the University of Missouri pulsed power test stand. Factors including the applied field, rate of rise and gas pressure of the switch along with the laser power, focused intensity, and Rayleigh range have been examined to determine their relation to jitter and runtime. The end goal of research is to understand the factors contributing to increased jitter and runtime and thereby provide paths to improved switch performance.College of Engineering Undergraduate Research Optio

Fundamental Science Investigations to Develop a 6-MV Laser Triggered Gas Switch for ZR: First Annual Report.

In October 2005, an intensive three-year Laser Triggered Gas Switch (LTGS) development program was initiated to investigate and solve observed performance and reliability issues with the LTGS for ZR. The approach taken has been one of mission-focused research: to revisit and reassess the design, to establish a fundamental understanding of LTGS operation and failure modes, and to test evolving operational hypotheses. This effort is aimed toward deploying an initial switch for ZR in 2007, on supporting rolling upgrades to ZR as the technology can be developed, and to prepare with scientific understanding for the even higher voltage switches anticipated needed for future high-yield accelerators. The ZR LTGS was identified as a potential area of concern quite early, but since initial assessments performed on a simplified Switch Test Bed (STB) at 5 MV showed 300-shot lifetimes on multiple switch builds, this component was judged acceptable. When the Z{sub 20} engineering module was brought online in October 2003 frequent flashovers of the plastic switch envelope were observed at the increased stresses required to compensate for the programmatically increased ZR load inductance. As of October 2006, there have been 1423 Z{sub 20} shots assessing a variety of LTGS designs. Numerous incremental and fundamental switch design modifications have been investigated. As we continue to investigate the LTGS, the basic science of plastic surface tracking, laser triggering, cascade breakdown, and optics degradation remain high-priority mission-focused research topics. Significant progress has been made and, while the switch does not yet achieve design requirements, we are on the path to develop successively better switches for rolling upgrade improvements to ZR. This report summarizes the work performed in FY 2006 by the large team. A high-level summary is followed by detailed individual topical reports

Ferroelectric Emission Cathodes for Low-Power Electric Propulsion

Low- or no-flow electron emitters are required for low-power electric thrusters, spacecraft plasma contactors, and electrodynamic tether systems to reduce or eliminate the need for propellant/expellant. Expellant-less neutralizers can improve the viability of very low-power colloid thrusters, field emission electric propulsion devices, ion engines, Hall thrusters, and gridded vacuum arc thrusters. The NASA Glenn Research Center (GRC) is evaluating ferroelectric emission (FEE) cathodes as zero expellant flow rate cathode sources for the applications listed above. At GRC, low voltage (100s to approx. 1500 V) operation of FEE cathodes is examined. Initial experiments, with unipolar, bipolar, and RF burst applied voltage, have produced current pulses 250 to 1000 ns in duration with peak currents of up to 2 A at voltages at or below 1500 V. In particular, FEE cathodes driven by RF burst voltages from 1400 to 2000 V peak to peak, at burst frequencies from 70 to 400 kHz, emitted average current densities from 0.1 to 0.7 A/sq cm. Pulse repeatability as a function of input voltage has been initially established. Reliable emission has been achieved in air background at pressures as high as 10(exp -6) Torr

Preliminary Results of Field Emission Cathode Tests

Preliminary screening tests of field emission cathodes such as chemical vapor deposited (CVD) diamond, textured pyrolytic graphite, and textured copper were conducted at background pressures typical of electric thruster test facilities to assess cathode performance and stability. Very low power electric thrusters which provide tens to hundreds micronewtons of thrust may need field emission neutralizers that have a capability of tens to hundreds of microamperes. From current voltage characteristics, it was found that the CVD diamond and textured metals cathodes clearly satisfied the Fowler-Nordheim emission relation. The CVD diamond and a textured copper cathode had average current densities of 270 and 380 mA/sq cm, respectively, at the beginning-of-life. After a few hours of operation the cathode emission currents degraded by 40 to 75% at background pressures in the 10(exp -5) Pa to 10(exp -4) Pa range. The textured pyrolytic graphite had a modest current density at beginning-of-life of 84 mA/sq cm, but this cathode was the most stable of all. Extended testing of the most promising cathodes is warranted to determine if current degradation is a burn-in effect or whether it is a long-term degradation process. Preliminary experiments with ferroelectric emission cathodes, which are ceramics with spontaneous electric polarization, were conducted. Peak current densities of 30 to 120 mA/sq cm were obtained for pulse durations of about 500 ns in the 10(exp -4) Pa pressure range

Modeling a gas puff z-pinch as an RL circuit load [abstract]

Abstract only availableA Z-pinch is process through which current is passed though a column of plasma and the resultant JxB force acts to "pinch" the plasma to smaller and smaller radii. More specifically, a gas puff Z-pinch is a Z-pinch that utilizes a puff of ionized gas (in this case hydrogen) to start the initial plasma. As the radius of the Z-pinch approaches zero the resistance and inductance of the pinch in the circuit change as a function of time. Through an iterative process of circuit simulations with PSpice, a function of the radius with respect to time can be determined. Using this information, the pinch can be modeled on the MU Terawatt Test Stand (MUTTS) as a load consisting of an inductor and a resistor. With this time-varying impedance the transient voltage and current can be graphed to determine the possibility of such a load in the future.College of Engineering Undergraduate Research Optio

X-ray and optical systems for pulsed power and plasma science experiments [abstract]

Abstract only availableX-ray imaging and detection are useful measurements, in familiar applications like dental X-rays and less familiar ones like elemental analysis. The Pulsed Power and Plasma Science group in the Electrical and Computer Engineering department at MU has assembled an x-ray detection system in order to measure x-rays generated from electrons striking a target at several keV. The detection system will be used to study x-ray emission from a ferroelectric plasma source. A DC electron gun, whose emission is carefully controlled, will be used as a known calibration source to compare to the ferroelectric plasma source. The results of the comparison are presented. In many pulsed power experiments, large amounts of electrical noise are produced, which make measurements difficult to obtain. Optical diagnostic systems are not subject to electrical noise and are very useful in these settings. A fast optical transmitter and receiver circuit was designed and built to transmit data in a noisy environment. The design and performance of this circuit is discussed.Undergraduate Honors Research in Engineerin

Thrust measurements of a ferroelectric plasma source [abstract]

Abstract only availableFerroelectric thrusters can be used in applications where small thrusts are useful such as guiding the movement of satellites. The Pulsed Power and Plasma Science group in the Electrical and Computer Engineering department at MU is characterizing a ferroelectric thruster in order to determine its range of maximum thrust. The thrust is measured using a Michelson interferometer and is in the order of 100µN. Both applied frequency and voltage directly affect the amount of thrust generated, and these variables will be varied to create a thrust operation curve. The thrust measurement technique and the resulting thrust curve is presented.College of Engineering Undergraduate Research Optio