Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Julian, Alexander L. Second Reader: Crisiti, Roberto. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Pulsed power, charger, buck converter, field programmable gate array (FPGA), lithium-ion batteries. Includes bibliographical references (p. 77-79). Also available in print.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Langmuir probes; spacecraft; electric propulsion. Includes bibliographical references (p.69-71).

The interaction of ultra-short laser pulses and cluster targets can be used to explore a number of interesting phenomena, ranging from nuclear fusion to astrophysical blast waves. In our experiments, we focused on exploring very fast plasma dynamics of a plasma created by ionizing clusters and monomer gas. By using a 115 fs laser pulse, we can even study sub-picosecond plasma dynamics. In addition, we also wanted to impose an external magnetic field on these plasmas to study how the plasma evolution would change. The results of this work produced two significant results. First, a new, extremely fast ionization mechanism, with velocities as high as 0.5 c, was discovered which allows for significant plasma expansion on a picosecond time-scale. Experimental studies measured the velocity of the ionization wave, while particle-in-cell simulations helped explain the source and longevity of the wave. It was also observed that this ionization wave was not affected by the external magnetic field. Second, the external field was shown to inhibit plasma expansion on a time-scale of tens of picoseconds, which seems to be one of the first demonstrations of magnetic confinement on such a fast time-scale. Simple 1D simulations tell us that the field appears to slow electron heat transport in the plasma as well as inhibiting collisional ionization of electrons expanding into the surrounding gas. The inhibition of plasma expansion by the field on this time-scale may provide some evidence that magnetic confinement of a fusion plasma created by exploding clusters could improve the fusion yield by slowing heat loss as well as possibly electrostatically confining the hot ions. / text

This thesis presents a study of a pulsed distributed arc plasma deposition method that has been developed to produce highly ionized pulsed plasma plumes of metallic species in the presence of a low-pressure inert or reactive gas glow discharge. A pulse-forming network (PFN) is used to form a transient electrical discharge in a hollow electrode which is triggered by two different methods; a pulsed CO2 laser or a pulsed high voltage glow discharge. With the PFN charged to a voltage of 70 - 100 VDC, current pulses with peak currents up to 3 kA and pulse widths as long 3.7 milliseconds have been reached. A detailed treatment of the influence of process parameters, such as the PFN discharge energy and ambient gas pressure and type, on the plasma properties is presented. These experiments also demonstrated a higher on-axis growth rate of carbon in an ambient of nitrogen than in argon. The higher argon mass leads to broader plasma expansion producing broader deposition profiles which results in lower on-axis growth rates. Deposition rates of 3.5 angstrom/pulse for carbon and 2.1 angstrom/pulse for titanium have been achieved. Thickness profiles and the morphology of carbon films and titanium films deposited by this method, which utilize the energetic advantage of ions in film formation allowing reduced substrate temperatures and good adhesion, are presented.

The work presented here discusses the effects of strong acoustic forcing on jet flames in crossflow (JFICF) and the physical mechanisms behind theses effects. For forced non-premixed JFICF, the jet fuel flow is modulated using an acoustic speaker system, which results in a drastic decrease in flame length and soot luminosity. Forced JFICF are characterized by periodic ejections of high-momentum, deeply penetrating vortical structures, which draws air into the jet nozzle and enhances mixing in the nearfield region of the jet. Mixture fraction images of the non-reacting forced jet in crossflow are obtained from acetone planar laser-induced fluorescence and show that the ejected jet fluid is effectively partially premixed. Flame luminosity images and exhaust gas measurements show that forced non-premixed JFICF exhibit similar characteristics to unforced partially-premixed JFICF. Both strong forcing and air dilution result in net reductions in NOx, but increases in CO and unburned hydrocarbons. NOx scaling analysis is presented for both forced non-premixed and unforced partially-premixed flames. Using flame volume arguments, EINOx scales with amplitude ratio for forced non- premixed flames, but does not scale with air dilution for unforced partially-premixed flames. The difference in scaling behavior is attributed to differences in flame structure. The effect of forcing on the flowfield dynamics of non-premixed JFICF is investigated using high-speed stereoscopic particle image velocimetry and luminosity imaging. The frequency spectra of the windward and lee-side flame base motions obtained from luminosity movies of the forced JFICF show a peak at the forcing frequency in the lee-side spectrum, but not on the windward-side spectrum. The lee-side flame base responds to the forcing frequency because the lee-side flame base stabilizes closer to the jet exit. The windward-side flame base does not respond to the forcing frequency because the integrated effect of the incident crossflow and vortical ejections leads to extinction of the flame base. From the PIV measurements, flowfield statistics are conditioned at the flame base. The local gas velocity at the flame base did not collapse for forced and unforced JFICF and was found to exceed 3SL. The flame propagation velocity was determined from the motion of the flame base, which is inferred from regions of evaporated seed particles in the time-resolved PIV images. The flame propagation velocity collapses for forced and unforced JFICF, which implies that the flame base is an edge flame; however, the most probable propagation velocity, approximately 2-3SL, is larger than propagation velocity predicted by edge flame theories. A possible explanation is that the flame propagation is enhanced by turbulent intensities and flame curvature. / text

No description available.

Bismuth-Strontium-Calcium-Copper-Oxide (BSCCO) compounds are an important family of compounds that have one of the highest transition temperatures among all high-temperature superconductors. The compound is known to exist in three distinct phases, commonly referred to as the 2201, 2212 and 2223 phases. Of these three phases, the 2212 and 2223 phases are the most important, as their transition temperature is higher than the boiling point of liquid nitrogen. It is desirable to produce the compound in thin film form, as the bulk samples are normally polycrystalline. This thesis compares thin films produced by two techniques for depositing BSCCO in order to understand the effect of various processing parameters on the final quality of the thin films. Thin films were grown by flash evaporation at Texas A&M University, and by pulsed laser deposition (PLD) at the University of Wollongong, Australia. The latter of these techniques is widely used for growing thin films of various compounds. Single-phase 2212 films were grown on a MgO substrate using the pulsed laser deposition technique from commercially available 2212 powder. The effect of annealing on the thin films was also studied.

In this Ph.D. thesis, we have carried out numerical simulations to study nanosecond repetitively pulsed discharges (NRPD) in a point-to-point geometry at atmospheric pressure in air and in H2-air mixtures. Experimentally, three discharge regimes have been observed for NRPD in air at atmospheric pressure for the temperature range Tg = 300 to 1000 K: corona, glow and spark. To study these regimes, first, we have considered a discharge occurring during one of the nanosecond voltage pulses. We have shown that a key parameter for the transition between the discharge regimes is the ratio between the connection-time of positive and negative discharges initiated at point electrodes and the pulse duration. In a second step, we have studied the dynamics of charged species during the interpulse at Tg = 300 and 1000 K and we have shown that the discharge characteristics during a given voltage pulse remain rather close whatever the preionization level (in the range 109-1011 cm��3) left by previous discharges. Then, we have simulated several consecutive nanosecond voltage pulses at Tg = 1000 K at a repetition frequency of 10 kHz. We have shown that in a few voltage pulses, the discharge reaches a stable quasi-periodic glow regime observed in the experiments. We have studied the nanosecond spark discharge regime. We have shown that the fraction of the discharge energy going to fast heating is in the range 20%- 30%. Due to this fast heating, we have observed the propagation of a cylindrical shockwave followed by the formation of a hot channel in the path of the discharge that expands radially on short timescales (t < 1 _s), as observed in experiments. Then we have taken into account an external circuit model to limit the current and then, we have simulated several consecutive pulses to study the transition from multipulse nanosecond glow to spark discharges. Finally the results of this Ph.D. have been used to find conditions to obtain a stable glow regime in air at 300 K and atmospheric pressure. Second we have studied on short time-scales (t_ 100_s) the ignition by a nanosecond spark discharge of a lean H2-air mixture at 1000 K and atmospheric pressure with an equivalence ratio of _ = 0:3. We have compared the relative importance for ignition of the fast-heating of the discharge and of the production of atomic oxygen. We have shown that the ignition with atomic oxygen seems to be slightly more efficient and has a completely different dynamics.

Diamond is widely known for its extraordinary properties, such as high hardness, thermal conductivity, electron mobility, energy bandgap and durability making it a very attractive material for many applications. Synthetic diamonds retain most of the attractive properties of natural diamond. Among the types of synthetic diamonds, nanocrystalline diamond (NCD) is being developed for electrical, tribological, optical, and biomedical applications. In this research work, NCD films were grown by the pulsed electron beam ablation (PEBA) method at different process conditions such as accelerating voltage, pulse repetition rate, substrate material and temperature. PEBA is a relatively novel deposition technique, which has been developed to provide researchers with a new means of producing films of equal or better quality than more conventional methods such as Pulsed Laser Deposition, Sputtering, and Cathodic Vacuum Arc. The deposition process parameters have been defined by estimating the temperature and pressure of the plasma particles upon impact with the substrates, and comparing the data with the carbon phase diagram. Film thickness was measured by visible reflectance spectroscopy technique and was in the range of 40 – 230 nm. The nature of chemical bonding, namely, the ratio (sp3/sp3+sp2) and nanocrystallinity percentage were estimated using visible Raman spectroscopy technique. The films prepared from the ablation of a highly ordered pyrolytic graphite (HOPG) target on different substrates consisted mainly of nanocrystalline diamond material in association with a diamond-like carbon phase. The micro-structural properties and surface morphology of the films were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The mechanical properties of the NCD films were evaluated by nano-indentation.