Modern Pulsed Power: Charlie Martin and Beyond

International Symposium on New Paradigm VLSI Computing, Sendai, Japan, Dec. 12-14, 2002, pp.31-36.This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. As such, it is in the public domain, and under the provisions of Title 17, United States Code, Section 105, may not be copyrighted.Modern pulsed power has its genesis in the pioneering work of the late John Christopher Martin and his colleagues at the Atomic Weapons Establishment, Aldermaston, U.K., in the 1960s [1]. “Charlie,” as he was known to the community, was a hydrodynamicist who was frustrated by his inability to purchase an adequate X-ray radiography source to image the dynamic phenomena he was interested in. As a result, he pursued a new generation of radiography sources that were based on high-power Marx generators, coupled with low-impedance transmission lines, and cold cathode single-stage accelerating gaps. Thus was the birth of modern pulsed power.U. S. Army Research OfficeSponsor/Monitor's Report Number(s):42713.8-PHDAAD19-01-1-069

Compact Pulsed-Power System for Transient Plasma Ignition

The article of record as published may be found at http://dx.doi.org10.1109/TPS.2009.2024672The use of a compact solid-state pulse generator and compact igniters for transient plasma ignition in a pulse detonation engine (PDE) is reported and compared with previous results using a pseudospark pulse generator and threaded rod electrode. Transient plasma is attractive as a technology for the ignition of PDEs and other engine applications because it results in reductions in ignition delay and has been shown to ignite leaner mixtures which allows for lower specific fuel consumption, high-repetition rates, high-altitude operation, and reduced NOx emissions. It has been applied effectively to the ignition of PDEs as well as internal combustion engines. Nonequilibrium transient plasma discharges are produced by applying high-voltage nanosecond pulses that generate streamers, which generate radicals and other electronically excited species over a volume. The pulse generator used is in this experiment is capable of delivering 180 mJ into a 200-Ω load, in the form of a 60-kV 12-ns pulse. Combined with transient plasma igniters comparable with traditional spark plugs, the system was successfully tested in a PDE, resulting in similar ignition delays to those previously reported while using a smaller electrode geometry and delivering an order of magnitude less energy.Office of Naval Researc

Transient Plasma Ignition of Quiescent and Flowing Air/Fuel Mixtures

Transient plasmas that exist during the formative phase of a pulse-ignited atmospheric pressure discharge were studied for application to ignition of quiescent and flowing fuel-air mixtures. Quiescent methane–air mixture ignition was studied as a function of equivalence ratio, and flowing ethane–air mixture was studied in a pulse detonation engine (PDE). The transient plasma was primarily comprised of streamers, which exist during approximately 50 ns prior to the formation of an equilibrated electron energy distribution. Results of significant reduction in delay to ignition and ignition pressure rise time were obtained with energy costs roughly comparable to traditional spark ignition methods (100–800 mJ). Reduction in delay to ignition by factors of typically 3 in quiescent mixes to 4 in a flowing PDE (0.35 kg/s), and other enhancements in performance were obtained. These results, along with a discussion of a pseudospark-based pulse generator that was developed for these applications, will be presented

Investigation of Transient Plasma Ignition

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 10 - 13 July 2005, Tucson, ArizonaReduction of auxiliary oxygen amounts currently used in Pulse Detonation Engines (PDEs) is necessary to compete with existing Ramjet technologies. This paper investigates a Transient Plasma Ignition (TPI) system and finds that this technology enables the complete removal of any auxiliary oxygen requirements of current PDE systems. TPI was tested and compared with a traditional capacitive discharge spark ignition system within ethylene/air mixtures under dynamic fill conditions. Successful operation was achieved at up-to 40Hz repetition rates. Ignition delay times, Deflagration-to-Detonation transition (DDT) distances and DDT times, detonation wave speeds, and detonation initiation success rates were measured and analyzed for various mass flow rates, for various ethylene-air mixtures, and for various lengths of turbulence generating Schelkhin spirals. A transient plasma dual- electrode concept was also investigated and analyzed. Results show that TPI system is more effective than conventional spark ignition systems. The TPI system shows near 20% improvements to DDT distances and up-to 2.5 reduction factor in DDT times. In addition, at high flow rates, where the flames normally extinguish when employing the spark ignition system, the TPI system was able to ignite mixtures and effectively initiate detonation waves. Detonation initiation success rates greater than 94% were obtained at cycle frequencies of up-to 40Hz. Further work is required to discern the TPI system sensitiv i ty to back pressures; additional instrumentation is requi red to determine axial variations in equivalence ratio

Transient Plasma Ignition for Delay Reduction in Pulse Detonation Engines

This presentation reviews testing and evaluation at four laboratories of transient plasma for pulse detonation engine (PDE) ignition, and presents data showing significant reductions in times required for detonation. The aerospace community has ongoing interests in the development of propulsion technologies based on pulse detonating engines (PDE), and work is underway to determine whether this is a feasible technology. The PDE provides impulse through fuel detonation, and potential advantages include efficient operation at both subsonic and supersonic speeds. In theory a PDE can efficiently operate from Mach 0 to more than Mach 4 [1,2]. In order to achieve almost continuous thrust firing rates of 100 Hz or more are needed. Critical to achieving high repetition rates are minimal delay to detonation times. In work supported by the Office of Naval Research and the Air Force Office of Scientific Research, transient plasma ignition (TPI) has consistently shown substantial reductions in ignition delay time for various fuels [3,4,5]. Experiments have been conducted at the University of Southern California and in collaboration with researchers at the Naval Postgraduate School, Wright Patterson Air Force Research Laboratory, Stanford University, the University of Cincinnati, and California Institute of Technology [6]. In these studies it was observed that TPI significantly reduces delay times in both static and flowing systems. Transient plasma ignition is attractive as an ignition source for PDEs because it produces reductions in ignition delay times, can reduce Deflagration to Detonation Transition (DDT) times, and has been shown to provide the capability to ignite under leaner conditions. This allows for high repetition rates, high altitude operation, and reduced NO, emissions [7,8]. The geometry of the discharge area is such that ignition is achieved with a high degree of spatial uniformity over a large volume relative to traditional spark ignition. The short timescale of the pulse ( < 100 ns) prevents formation of an arc, and a voluminous array of streamers is used for ignition. It is possible that energetic electrons in the highly non-equilibrated electron energy distribution of the streamers cause dissociation of hydrocarbon chain molecules, producing active radicals throughout the ignition volume [9]. A further advantage of TPI is that a smaller fraction of the electrical energy goes into thermal heating of the mixture. These effects allow for large numbers of active species to be generated throughout the volume

Transient Plasma Ignition for Delay Reduction in Pulse Detonation Engines

45th AIAA Aerospace Sciences Meeting and Exhibit 8 - 11 January 2007, Reno, NevadaThis paper reviews the testing and evaluation of transient plasma for pulse detonation engine (PDE) ignition conducted at five laboratories. It also presents data showing significant reductions in times required for detonation. Critical to achieving functional levels of thrust are increased repetition rates, thus minimal delay to detonation times are an important parameter. Experiments have been conducted at the University of Southern California and in collaboration with researchers at the Naval Postgraduate School, Wright Patterson Air Force Research Laboratory, Stanford University, Ohio State University and the University of Cincinnati. In these studies it was observed that TPI significantly reduces delay times (factor of 2 to 9) in both static and flowing systems

A Bright Submillimeter Source in the Bullet Cluster (1E0657--56) Field Detected with BLAST

We present the 250, 350, and 500 micron detection of bright submillimeter emission in the direction of the Bullet Cluster measured by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). The 500 micron centroid is coincident with an AzTEC 1.1 mm point-source detection at a position close to the peak lensing magnification produced by the cluster. However, the 250 micron and 350 micron centroids are elongated and shifted toward the south with a differential shift between bands that cannot be explained by pointing uncertainties. We therefore conclude that the BLAST detection is likely contaminated by emission from foreground galaxies associated with the Bullet Cluster. The submillimeter redshift estimate based on 250-1100 micron photometry at the position of the AzTEC source is z_phot = 2.9 (+0.6 -0.3), consistent with the infrared color redshift estimation of the most likely IRAC counterpart. These flux densities indicate an apparent far-infrared luminosity of L_FIR = 2E13 Lsun. When the amplification due to the gravitational lensing of the cluster is removed, the intrinsic far-infrared luminosity of the source is found to be L_FIR <= 10^12 Lsun, consistent with typical luminous infrared galaxies.Comment: Accepted for publication in the Astrophysical Journal. Maps are available at http://blastexperiment.info

Over half of the far-infrared background light comes from galaxies at z >= 1.2

Submillimetre surveys during the past decade have discovered a population of luminous, high-redshift, dusty starburst galaxies. In the redshift range 1 <= z <= 4, these massive submillimetre galaxies go through a phase characterized by optically obscured star formation at rates several hundred times that in the local Universe. Half of the starlight from this highly energetic process is absorbed and thermally re-radiated by clouds of dust at temperatures near 30 K with spectral energy distributions peaking at 100 microns in the rest frame. At 1 <= z <= 4, the peak is redshifted to wavelengths between 200 and 500 microns. The cumulative effect of these galaxies is to yield extragalactic optical and far-infrared backgrounds with approximately equal energy densities. Since the initial detection of the far-infrared background (FIRB), higher-resolution experiments have sought to decompose this integrated radiation into the contributions from individual galaxies. Here we report the results of an extragalactic survey at 250, 350 and 500 microns. Combining our results at 500 microns with those at 24 microns, we determine that all of the FIRB comes from individual galaxies, with galaxies at z >= 1.2 accounting for 70 per cent of it. As expected, at the longest wavelengths the signal is dominated by ultraluminous galaxies at z > 1.Comment: Accepted to Nature. Maps available at http://blastexperiment.info