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Plasma Science, IEEE Transactions on

Issue 2 • Date April 2005

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Displaying Results 1 - 25 of 42
  • Table of contents

    Publication Year: 2005 , Page(s): c1 - 589
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  • IEEE Transactions on Plasma Science publication information

    Publication Year: 2005 , Page(s): c2
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  • Editorial

    Publication Year: 2005 , Page(s): 590 - 592
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  • Ion temperature imaging of the Earth's magnetosphere

    Publication Year: 2005 , Page(s): 593 - 598
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    Detection of neutral atom emission from hot plasmas has evolved to the point where it is now possible to image hot plasmas in neutral atom emission. In this paper, we review the qualitative and quantitative spatially resolved information that can be obtained from neutral atom images, e.g., hot ion transport and ion temperatures. A challenging aspect of neutral atom imaging of the earth's quiet time magnetosphere is that the combination of small neutral fluxes and spacecraft motion necessitates the development of algorithms capable of summing neutral emission obtained from different vantage points over many months to obtain statistically significant images. The image summing algorithm and typical summed images are also presented in this work. View full abstract»

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  • Electromagnetic bounded States and challenges of plasma spectroscopy

    Publication Year: 2005 , Page(s): 599 - 608
    Cited by:  Papers (4)
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    We review the foundations and observational support for a new plasma wave mode that has been proposed to explain emissions stimulated by satellite-born high-power radio-frequency sounders. These sounders, which are designed to derive remote electron density profiles from electromagnetic-wave echoes, stimulate plasma resonances in the local plasma. In addition to stimulating resonances at the electron plasma frequency fpe, harmonics of electron gyrofrequency fce, and at the upper hybrid frequency fuh, resonances are also stimulated at frequencies below fpe between the gyroharmonics. The first such resonance, with frequency between fce and 2fce, was discovered by Nelms and Lockwood in 1967 using the topside sounder on Alouette 2. From its appearance, it was called a diffuse resonance (D1 in modern notation) and was originally thought to have a frequency of 3/2fce. Further observations, and theoretical insights, indicated that fD1 is dependent on fpe and fce, namely, fD1=(3/π)(fpefce)12/. The theoretical concepts used to obtain this expression indicated that the Dn resonances (n=1,2,3,...) are electron eigenmodes (electromagnetic bounded states) and led to equations describing the frequencies of the entire Dn sequence and their subsidiary resonances Dn+ and Dn-. Such formulas, based on a combined theoretical and empirical approach, describe a √n spectrum with the frequency of each mode split by the magnetic field analogous to the Zeeman splitting in quantum mechanics. The √n spectrum was first predicted for force-free electromagnetic cylindrical plasma oscillations by Osherovich in 1986. The main theoretical challenge remains to derive the frequency fD1 from first principles. Although the Dn resonances have been stimulated in the terrestrial ionosphere for decades by topside sounder satellites such as Alouette 2 and by electron guns on several rocket experiments, and in Jupiter's Io plasma torus by the sounder on the Ulysses space probe, and are currently being stimulated in the terrestrial magnetosphere by the sounder on the IMAGE spacecraft, they have yet to be observed in laboratory experiments. View full abstract»

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  • δf Simulation of the collisionless tearing mode instability with a gyrokinetic ion response

    Publication Year: 2005 , Page(s): 609 - 614
    Cited by:  Papers (1)
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    The evolution of the collisionless tearing mode instability is studied using an electromagnetic gyrokinetic δf particle-in-cell simulation model. Drift-kinetic electrons are used. High resolution, small box (less than 10 ion gyroradii) simulations have been well benchmarked with eigenmode analysis and their nonlinear evolution agrees well with theory. In this regime, the ion response is not important and can be either fixed, adiabatic or fully gyrokinetic. Here, results are presented with larger box sizes (64 ion gyroradii radially) where the ion gyrokinetic response is important and cannot be neglected. In these larger box simulations, the instability exhibits an odd parity, different than the even tearing parity. View full abstract»

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  • Transition between different modes of a capacitively coupled radio frequency discharge in CH4 in one- and two-dimensional PIC-MCC Simulations

    Publication Year: 2005 , Page(s): 615 - 623
    Cited by:  Papers (1)
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    Two regimes of a capacitevely coupled radio frequency (CCRF) gas discharge operating in methane are studied with a combined particle-in-cell Monte Carlo collisions (PIC-MCC) algorithm (one-dimensional model) and with accelerated PIC-MCC algorithm (two-dimensional model) for gas pressure P=(0.01--1) torr and discharge current j=(0.45--2.2) mA/cm2. The areas of existence of different discharge regimes are shown on a P-j phase diagram and compared with known numerical results. The role secondary electrons from electrodes during transition is discussed. The phenomena of hysteresis is observed in discharge behavior with current change over growing and falling current branches. View full abstract»

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  • Mode Characteristics of radio-frequency atmospheric glow discharges

    Publication Year: 2005 , Page(s): 624 - 630
    Cited by:  Papers (44)
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    Building on recent experimental and numerical evidence of different glow modes in atmospheric plasmas, this paper reports a systematic study of these modes in radio-frequency (RF) glow discharges in atmospheric helium. Using a one-dimensional (1-D) hybrid computer model, we present detailed characterization of three glow modes, namely the α mode, the α-γ transitional mode, and the γ-mode in a 13.56-MHz atmospheric glow discharge over a wide range of root mean square (RMS) current density from 5 mA/cm2 to 110 mA/cm2. Our focus is on sheath dynamics through spatial and temporal profiles of charged densities, electric field, electron mean energy, sheath thickness, and sheath voltage, and when appropriate our results are compared against experimental data of atmospheric glow discharges and that of glow discharges at reduced gas pressure below 1 torr. Fundamental characteristics of the three glow modes are shown to be distinctively different, and these can be used as a hitherto unavailable route to tailor the operation of radio-frequency atmospheric glow discharges to their intended applications. View full abstract»

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  • Presheath environment in weakly ionized single and multispecies plasmas

    Publication Year: 2005 , Page(s): 631 - 636
    Cited by:  Papers (11)
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    The presheath located near boundaries in weakly ionized plasmas is a rich environment in which charge exchange, and ion-ion streaming instabilities combine to establish the electric fields that accelerate ions to close to the Bohm velocity at the sheath/presheath boundary. Charge exchange sets the presheath scale length in weakly collisional plasma, in which ionization can be neglected. The transition of mobility limited ion flow near the bulk plasma to free fall motion close to the plate for single species plasmas is explored. Measurements in argon-helium multidipole plasmas of plasma potential with emissive probes and ion energy distribution functions with laser induced fluorescence are presented. These data show that the argon ions are speeded up by the presheath electric fields, argon ions are heated, and ion-ion instability is present as ions approach the boundary. View full abstract»

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  • Whistler wave propagation and whistler wave antenna radiation resistance measurements

    Publication Year: 2005 , Page(s): 637 - 646
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB) |  | HTML iconHTML  

    Whistler waves are a common feature of ionospheric and magnetospheric plasmas. While the linear behavior of these waves is generally well understood, a number of interesting observations indicate that much remains to be learned about the nonlinear characteristics of the mode. For example, in space, very low frequency (VLF) emissions triggered by whistler modes launched from ground-based transmitters have been observed. Emission is assumed to come from transverse currents formed by counterstreaming electrons that are phase bunched by the triggering signal. In the laboratory, it has been shown that with increasing amplitude of the driving signal applied to an antenna, the whistler mode radiation pattern forms a duct with diameter of the order of the parallel wavelength. The ducted waves were observed to propagate virtually undamped along the length of the plasma column. These observations have prompted an Naval Research Laboratory's (NRL) Space Physics Simulation Chamber study of whistler wave dynamics. The goals are to investigate whistler wave ducting, self-focusing, and amplification, and to study nonlinear whistler-plasma interactions. View full abstract»

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  • Design of a gridded gun and PPM-focusing structure for a high-power sheet electron beam

    Publication Year: 2005 , Page(s): 647 - 653
    Cited by:  Papers (13)
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    We describe the design of a gridded electron gun and periodic permanent magnet (ppm)-focusing structure to create and guide a 415-kV, 250-A sheet beam with a cross section of 100 mm × 8 mm. The gun is intended for use with a 40-MW X- band sheet beam klystron for driving accelerators. Using the three-dimensional (3-D) code suite AMAZE, we designed a ppm structure that guided the beam over 80 cm with 98% transmission. View full abstract»

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  • Rapid kinematic bunching and parametric instability in a crossed-field gap with a periodic magnetic field

    Publication Year: 2005 , Page(s): 654 - 660
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    Single particle orbit considerations show that the cycloidal orbits of electrons in a gap with crossed electric and magnetic fields lead to rapid spoke formation if the external magnetic field has a periodic variation. This spoke formation is primarily a result of kinematic bunching, which is independent of the radio frequency electric field and of the space charge field. A parametric instability in the orbits, which brings a fraction of the electrons from the cathode to the anode region, is discovered. These results are examined in light of the recent rapid startup, low noise magnetron experiments and simulations that employed periodic, azimuthal perturbations in the axial magnetic field. View full abstract»

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  • Microwave pulse compression using a helically corrugated waveguide

    Publication Year: 2005 , Page(s): 661 - 667
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB) |  | HTML iconHTML  

    There has been a drive in recent years to produce ultrahigh power short microwave pulses for a range of applications. These high-power pulses can be produced by microwave pulse compression. Sweep-frequency based microwave pulse compression using smooth bore hollow waveguides is one technique of passive pulse compression, however, at very high powers, this method has some limitation due to its operation close to cutoff. A special helical corrugation of a circular waveguide ensures an eigenwave with strongly frequency dependent group velocity far from cutoff, which makes the helically corrugated waveguide attractive for use as a passive pulse compressor for very high-power amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a particle in cell particle-in-cell (PIC) code are presented. In the experiments, a 70-ns 1-kW pulse from a conventional traveling-wave tube (TWT) was compressed in a 2-m-long helical waveguide. The compressed pulse had a peak power of 10.9 kW and duration of 3 ns. In order to find the optimum pulse compression ratio, the waveguide's dispersion characteristics must be well known. The dispersion of the helix was calculated using the PIC code Magic and verified using an experimental technique. Future work detailing plans to produce short ultrahigh power gigawatt (GW) pulses will be discussed. View full abstract»

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  • Joining of ceramic tubes using a high-power 83-GHz Millimeter-wave beam

    Publication Year: 2005 , Page(s): 668 - 678
    Cited by:  Papers (8)  |  Patents (1)
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    High purity, high density alumina tubes have been successfully joined using a high-power millimeter-wave beam. This technique exploits the use of the beam-forming capability of an 83-GHz gyrotron-based system allowing the deposition of energy into a narrow region surrounding the joint area with minimal heating (<100°C) of the metal fixturing (a modified microlathe). The power deposition and heating was modeled using a closed form analytical approach that has been compared with experimental results. The modeling results indicated areas of improvement that were implemented to make the process more effective. Conjoined tubes resulting from this technology meet the requirements for the dielectric-loaded accelerator (DLA) being developed by the Argonne National Laboratory. View full abstract»

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  • Experimental investigations on miniaturized high-frequency vacuum electron devices

    Publication Year: 2005 , Page(s): 679 - 684
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB) |  | HTML iconHTML  

    We investigated the foundations for high-frequency vacuum electron devices experimentally, with emphasis on deep etch X-ray lithography: lithographie, galvanoformung, abformung (LIGA) to fabricate a miniaturized interaction circuit and a photonic crystal (PC) resonator to excite a stable high-order mode. The successful operation of a LIGA-fabricated folded-waveguide traveling-wave tube was reported. From such physical considerations as Debye length and photonic band gap, we proposed a reflex klystron adopting a cold cathode and a PC resonator. View full abstract»

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  • Eighteen-beam gun design for high power, high repetition rate, broadband multiple-beam klystrons

    Publication Year: 2005 , Page(s): 685 - 695
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB) |  | HTML iconHTML  

    This paper presents the design of a high repetition rate electron gun to be employed in future high-power broadband multiple-beam amplifiers operating in S-band. Special emphasis is placed on the geometric layout of the gun to ensure high repetition rate operation at moderate beam switching voltages, good beam optics, and optimal beam packing for long life, efficient beam-wave interaction and broad bandwidth. The resulting gun design employs an eighteen-beam magnetically shielded cathode topology capable of generating a total current of 41.6 A (evenly divided among eighteen beams) at a voltage of 42 kV. In the beam tunnels, each beamlet has a radial fill factor of 48%. The nominal beam modulation voltage is 5.2 kV. With an estimated gun capacitance of 150 pF, a repetition rate in excess of 10 kHz is feasible with the current state-of-the-art in modulator technology. View full abstract»

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  • Characterization of a self-magnetic-pinched diode

    Publication Year: 2005 , Page(s): 696 - 703
    Cited by:  Papers (8)
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    Self-magnetic-pinched diode behavior at 1.5-2 MV was diagnosed using a variety of electrical, radiation, and optical diagnostics. Results are compared with predictions of the LSP particle-in-cell code, and shown to be in good agreement. A practical diagnostic of electron incidence angles is demonstrated. A quadrature interferometer is shown to be capable of measuring the time-dependent position of the effective electrode-plasma boundaries. Both one-dimensional (1-D) and two-dimensional (2-D) interferometry show the importance of anode plasma expansion in such diodes with high anode-power concentration. Not only does the anode plasma contribute significantly to gap closure, but there is evidence that anode plasma expansion results in a distortion of the effective anode shape, which can significantly affect the diode performance. View full abstract»

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  • Paraxial gas-cell focusing of relativistic electron beams for radiography

    Publication Year: 2005 , Page(s): 704 - 711
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    A description of the underlying physics governing the operation of pulsed-power driven, gas-filled, paraxial diodes is presented. Gas-filled focusing cells are routinely used to transport high energy density electron beams for use in flash X-ray radiography experiments. The paraxial diode acts as a 1/4 betatron focusing element with a focal length F proportional to the square root of the beam energy and inversely proportional to the square root of the net current in the gas cell F∝(γ/Inet)12/. Particle-in-cell simulations demonstrate that the time integrated radiation spot is determined both by focal sweeping due to time varying net currents and by finite beam emittance. The calculated radiation focal plane, spot, and dose are compared to data obtained by the Atomic Weapons Establishment, U.K., from a variety of experimental configurations and demonstrate good agreement between simulation and experiment. Suggestions to improve the focal properties of the diode are presented. View full abstract»

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  • Trapping and acceleration of nonideal injected electron bunches in laser Wakefield accelerators

    Publication Year: 2005 , Page(s): 712 - 722
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    Most conceptual designs for future laser wakefield accelerators (LWFA) require external injection of precisely-phased, monoenergetic, ultrashort bunches of MeV electrons. This paper reports simulation and Hamiltonian models of several nonideal injection schemes that demonstrate strong phase bunching and good accelerated beam quality in a channel-guided LWFA. For the case of monoenergetic, unphased (long bunch) injection, there is an optimum range of injection energies for which the LWFA can trap a significant fraction of the injected pulse while producing an ultrashort, high-quality accelerated pulse. These favorable results are due to a combination of pruning of particles at unfavorable phases, rapid acceleration, and strong phase bunching. Also, the plasma channel introduces a favorable shift in the region of accelerating phase where electrons are focused, which can significantly reduce the required injection energy. Simulation results agree well with the predictions of the Hamiltonian model. Simulations of phased injection with a broad injected energy spread also exhibit final accelerated bunches with small energy spread. These results suggest that relatively poor quality injection pulses may still be useful in LWFA demonstration experiments. View full abstract»

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  • Initial studies of steady inductive helicity injection on the HIT-SI experiment

    Publication Year: 2005 , Page(s): 723 - 728
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB) |  | HTML iconHTML  

    The helicity-injected torus (HIT-SI) is designed to produce a "bow tie" spheromak, formed and sustained by steady inductive helicity injection (SIHI) current drive (Jarboe, 1999). SIHI is implemented via two "helicity injectors." Each injector acts as a 180° segment of a reversed-field pinch (RFP), with a typical peak current of 11 kA and a peak flux of 0.5 mWb. The toroidal loop voltage, toroidal injector plasma current, and toroidal flux of a single injector all oscillate sinusoidally at a frequency of 5 kHz and nearly in phase, so the single injector helicity injection rate and power input to the plasma are always positive. Operating the two injectors 90° out of phase in time provides nearly constant power input and helicity injection rate. To date, injector plasmas have been sustained in this manner for over 5 ms. An internal magnetic probe array has been installed in one of the injectors. Observations of the injector fields will be presented, illustrating the evolution of the field structure through the injector cycle. View full abstract»

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  • Continued development of a 12-cm-diameter nozzle for argon Z-pinches

    Publication Year: 2005 , Page(s): 729 - 734
    Cited by:  Papers (2)
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    We report on the variation of K-shell X-ray output of an argon Z-pinch as a function of the radial gas distribution. The tests, conducted on the Double-EAGLE simulator at ∼3.5-MA peak current, utilized a 12-cm-diameter double-shell nozzle that was designed for use with the 300-ns rise-time current pulse (∼6 MA) of the DECADE QUAD pulsed power machine. By varying the plena gas pressures of the inner and outer shells, the net radial distribution could be changed from one that was strongly concentrated near the axis to one more broadly distributed as a function of radius. Previous work has shown that a roughly uniform radial distribution gives higher X-ray output than shell-like flows for gas Z-pinches. The present work was focused on refining the optimum radial distribution and to establish benchmarks for modeling calculations. The present data show that the K-shell yield has a broad optimum (and the relative strength of the K continuum >4 keV systematically changes) as the mass distribution becomes more peaked near the axis. Very-high-quality K-emitting volumes (<5 ns pulse width from <1 mm diameters) were achieved over a significant fraction of the pinch length. View full abstract»

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  • Generation of high-energy electrons in a double gas jet and laser wakefield acceleration

    Publication Year: 2005 , Page(s): 735 - 738
    Cited by:  Papers (3)
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    High-energy electrons were generated by the synchronized interaction of a 2-TW laser beam with a nitrogen gas jet and a 10-TW laser beam with helium gas jet. The jets centers are separated by 0.5 mm distance and the propagation of the lasers are collinear. Plasma electrons were trapped and accelerated by the wakefields generated in the gas jet plasmas to above 20 MeV. View full abstract»

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  • Heating of on-axis plasma heating for keV X-ray production with Z-pinches

    Publication Year: 2005 , Page(s): 739 - 751
    Cited by:  Papers (17)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    We discuss a new opportunity of using Z-pinch plasma radiation sources for generating Ar K-shell radiation and harder keV quanta. Our approach to keV X-ray generation is based upon an analogy with laser fusion, where the imploding shell compressionally heats the low-density inner mass. The suggested design of a Z-pinch load consists then of one or two heavy outer shell(s) with a lower mass on-axis fill (i.e., central gas jet) producing most of the radiation. The outer shell is not supposed to radiate and thus does not need to have high specific energy characterized by the large η parameter (Whitney et al., 1990). Thus, the heavy outer shell does not need to have a very large initial diameter for its implosion to be matched to the long-pulse current driver. Rather, we want to have a large amount of energy from the driver coupled to this shell by the moment when the shell collides with the low-density fill and eventually converts much of this energy to the thermal energy of the on-axis plasma. This configuration is investigated numerically in the framework of a one-dimensional radiation-magneto-hydrodynamics model for the case of Ar K-shell radiators. It is demonstrated that the Ar fill is heated in two stages. The first stage corresponds to the shock heating and thermal conduction in an initially low-density fill, and it allows preheating the fill while avoiding significant losses in soft radiation. The fill radiator is then compressed quasi-adiabatically and is heated-up to the temperature optimum for K-shell quanta generation. Diffusion of the driving magnetic field is shown to always suppress the conductive heat losses from the hot on-axis plasma to the cold outer shell. Absorption of the K-lines emitted near the axis in the surrounding plasma could be avoided by filling the outer shell with a different gas (like N-on-Ar), which allows a substantial increase in the observed keV X-ray radiation yields. View full abstract»

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  • Two-dimensional gas density and velocity distributions of a 12-cm-diameter, triple-nozzle argon Z-pinch load

    Publication Year: 2005 , Page(s): 752 - 762
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2000 KB)  

    We have developed a 12-cm-diameter Ar gas Z-pinch load, which produces two annular gas shells and a center gas jet. The two-dimensional (2-D) gas density profiles of the load, in r-θ and r-z planes, were measured with submillimeter spatial resolutions using the planar-laser-induced fluorescence (PLIF) method, for conditions used in Z-pinch experiments. Due to interactions between the shells, the net gas density profile differs from the superposition of the individual shell profiles. Narrow density peaks are observed both at smaller and larger radii than the radius where the shells come in contact with each other. Two-dimensional flow velocity distributions are determined from the displacements between the fluorescence and later time phosphorescence images. The measured stream velocities of argon gas puffs are 650 ± 20 m/s, higher than the ideal gas velocity due to the formation of clusters in the supersonic gas flow. Indeed, clusters were observed in earlier Rayleigh scattering experiments. The gas measurements of the initial phase using the PLIF will be combined with other density measurements of the implosion and pinch phases to better understand the implosion dynamics and to provide initial conditions for simulation codes. View full abstract»

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  • Correlation of energy efficiency of NO removal by intermittent DBD radical injection method

    Publication Year: 2005 , Page(s): 763 - 770
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    Ammonia radicals are produced by a dielectric barrier discharge (DBD) in a chamber separate from the chamber that NO gas flows, and are injected in the NO gas flowing field to decompose NO gas. The power source for generating the DBD is a one-cycle sinusoidal (OCS) waveform so as to easily control the power consumed in the DBD plasma. The fundamental frequency of the OCS power source is 150 kHz. The correlation of the DeNOx characteristics was discussed, where the residence time of the ammonia gas in the radical injector and the power density consumed in the DBD plasma were considered. Their product was called residence energy density (RED). It was confirmed that the parametric data of the DeNOx energy efficiency were clearly correlated by the RED. Currently, the energy efficiency of 250 g/kWh was attained at a NO gas temperature of 600°C. In order to obtain a high-energy efficiency in this system, the suppression of the energy consumed in the DBD plasma is effective, and instead, the ammonia flow rate decreases, compensating the accepted energy of the ammonia particles by the residence in the radical injector. View full abstract»

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Aims & Scope

IEEE Transactions on Plasma Sciences focuses on plasma science and engineering, including: magnetofluid dynamics and thermionics; plasma dynamics; gaseous electronics and arc technology.

 

 

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Meet Our Editors

Editor-in-Chief
Steven J. Gitomer, Ph.D.
Senior Scientist, US Civilian Research & Development Foundation
Guest Scientist, Los Alamos National Laboratory
1428 Miracerros Loop South
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