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Plasma Science, IEEE Transactions on

Issue 3 • Date March 2009

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Displaying Results 1 - 18 of 18
  • Table of contents

    Page(s): C1 - 389
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  • IEEE Transactions on Plasma Science publication information

    Page(s): C2
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  • Design of an Energy Recovery System for a Gyrotron Backward-Wave Oscillator

    Page(s): 390 - 394
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (681 KB) |  | HTML iconHTML  

    To realize the full potential of a gyrotron backward-wave oscillator (gyro-BWO), an energy recovery system was designed using Particle-In-Cell (PIC) simulations and optimized using both a genetic algorithm and PIC simulations. Simulations were carried out to optimize a periodic structure for separation of the spent electron beam and the output radiation produced by a gyro-BWO in the 8.0-9.5 GHz frequency range. The spent electron beam can be collected using a multistage depressed collector. The number and electric potentials of the electrodes were optimized to achieve the best overall recovery efficiency for specific parameters of the spent beam. The 3-D PIC code MAGIC was used to simulate the electrons' trajectories and a genetic algorithm was used to refine the electrode shapes for optimum efficiency. View full abstract»

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  • Progress and First Results With the New Multifrequency ECRH System for ASDEX Upgrade

    Page(s): 395 - 402
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (821 KB) |  | HTML iconHTML  

    A multifrequency electron cyclotron resonance heating (ECRH) system is currently under construction at the ASDEX Upgrade tokamak experiment. The system employs depressed collector gyrotrons, step tunable in the range of 105-140 GHz, with a maximum output power of 1 MW and a pulse length of 10 s. One two-frequency GYCOM gyrotron has been in routine operation at ASDEX Upgrade since 2006. A further extension of the system with three more gyrotrons is underway. An in situ calibration scheme for the broadband torus window has been developed. The system is equipped with fast steerable mirrors for real-time MHD control. The gyrotron and the mirrors are fully integrated into the discharge control system. The ECRH system turned out to be essential for the operation of H-modes after covering the plasma facing components of ASDEX Upgrade with tungsten. Deposition of ECRH inside rhotor < 0.2 is necessary to prevent accumulation of W in plasmas with high pedestal temperatures. With respect to the limited loop voltage available in ITER, the use of ECRH for neutral-gas preionization to facilitate plasma breakdown and its application during the current ramp-up to increase the conductivity in order to save transformer flux have been demonstrated successfully for 105 GHz, 3.2 T (O1-mode) and 140 GHz, 2.2 T (X2-mode), corresponding to 170 GHz at ITER with the full and half values of its foreseen toroidal field of 5.3 T. View full abstract»

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  • Theoretical Investigation of Iterative Phase Retrieval Algorithm for Quasi-Optical Millimeter-Wave RF Beams

    Page(s): 403 - 413
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    In this paper, we present a detailed analysis of the iterative phase retrieval approach (IPRA) for determining the phase profile of the output microwave beam of a gyrotron from known intensity patterns emphasizing the field propagation techniques which are used to propagate the RF field of the microwave beam between known intensity planes. The propagation method, based on first Rayleigh-Sommerfeld diffraction integral (RSDI), is solved using fast Fourier transform (FFT) technique and zero padding. It is observed that the use of FFT and, therefore, the discretization of the RSDI propagation kernel introduce aberrations in the propagated field due to the superposition of the original field with its replicated versions. This problem is solved by approximations leading to the Huygens-Fresnel propagation method which further imposes the restrictions on the distances of propagation depending on the size of the transverse plane used to discretize the intensity pattern. This constraint of the distance of propagation causes problem in the iterative phase retrieval approach (IPRA) when more than two intensity planes are used. A method based on interpolation is proposed to overcome this restriction. IPRA is then further discussed to optimize several parameters, such as plane separation, plane dimension, mesh size, and measurement accuracies, which become more of an issue during the measurements of infrared intensity thermograms of the output microwave beam. View full abstract»

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  • Infrared Measurements of the RF Output of 170-GHz/2-MW Coaxial Cavity Gyrotron and Its Phase Retrieval Analysis

    Page(s): 414 - 424
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    We report the experimental results of the infrared measurements of output RF beam of the European 2-MW 170-GHz coaxial cavity gyrotron for ITER. The output beam profile is measured by the infrared thermographic technique using an infrared camera and a target material which is being irradiated by the RF output. The beam intensity was measured at several locations along the propagation direction. The data were processed for noise reduction and perspective correction and then used with the phase retrieval algorithm to yield an accurate estimate of the phase profile. The moments of the measured intensity arrays are calculated to improve the reliability of the measured infrared image data and data processing. The beam profile is also measured at specific locations in order to compare the phase calculated with the Huygens-Fresnel propagation method for fixed distance and Rayleigh-Sommerfeld diffraction integral method used for field propagation in the phase retrieval algorithm. View full abstract»

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  • Neutron Energy Distribution Function Reconstructed From Time-of-Flight Signals in Deuterium Gas-Puff Z -Pinch

    Page(s): 425 - 432
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (952 KB) |  | HTML iconHTML  

    The implosion of a solid deuterium gas-puff Z-pinch was studied on the S-300 pulsed power generator [A. S. Chernenko, , Proceedings of 11th Int. Conf. on High Power Particle Beams, 154 (1996)]. The peak neutron yield above 1010 was achieved on the current level of 2 MA. The fusion neutrons were generated at about 150 ns after the current onset, i.e., during the stagnation and at the beginning of the expansion of a plasma column. The neutron emission lasted on average 25 ns. The neutron energy distribution function was reconstructed from 12 neutron time-of-flight signals by the Monte Carlo simulation. The side-on neutron energy spectra peaked at 2.42 plusmn 0.04 MeV with about 450-keV FWHM. In the downstream direction (i.e., the direction of the current flow from the anode toward the cathode), the peak neutron energy and the width of a neutron spectrum were 2.6 plusmn 0.1 MeV and 400 keV, respectively. The average kinetic energy of fast deuterons, which produced fusion neutrons, was about 100 keV. The generalized beam-target model probably fits best to the obtained experimental data. View full abstract»

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  • Investigation of Carbon X -Pinches as a Source for Point-Projection Radiography

    Page(s): 433 - 437
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    We report on the first investigations of the use of carbon fibers in an X-pinch load using a 250-kA linear transformer driver (LTD). Multiframe laser shadowgraphy is used to examine the evolution of the pinch and shows that carbon loads demonstrate wire expansion and cross-point pinch and gap formation as observed in X-pinches constructed from high Z materials. Radiographs taken using the carbon X-pinch as the source demonstrate both that sufficient flux is emitted to provide a good contrast image at source-to-image distances of > 10 cm and that the cross point produces a relatively small hot spot. Radiographs of a series of fine wires (5-30 mum) using X-rays > 500 eV demonstrated that 25-mum wires can be resolved in this energy range. Time-resolved X-ray emission measurements showed that, while emission in the hnu > 500 eV range shows long (> 100 ns) timescales, emission in the hnu > 1 keV range shows a multiple-peaked structure with durations as short as 20 ns. View full abstract»

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  • Plasma Diffusion Along a Fine Tube Positive Column

    Page(s): 438 - 443
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    The propagation velocity of light emission is observed to be up ~0.92 times10+5 m/s along a tube of an inner diameter ro ~1.5 times10-3 m with an external electrode fluorescent lamp filled with 97% Ne and 3% Ar at a total pressure of 30 torr, a mercury-free lamp without phosphor coating the inside glass wall. The origin of this propagation is shown to be ambipolar diffusion with a plasma diffusion speed of up ~ (4.8/ro)Da for diffusion coefficient Da along the positive column. When a high voltage magnitude is applied at the external electrode, a high-density plasma is generated inside the hollow electrode, and the plasma diffuses along the positive column toward the ground electrode. View full abstract»

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  • Analysis of the By-Products in the Ammonia Production From Urea by Dielectric Barrier Discharge

    Page(s): 444 - 448
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    Ammonia, which is the main product of urea decomposition, is used as the reducing agent in the gas phase plasma NOx treatment. Urea, because of its cheap price and relatively low decomposition temperature (150degC ), represents an excellent direct source of ammonia. In a dielectric barrier discharge (DBD), such temperatures can be achieved within a few minutes of applying voltage. This paper deals with the chemical analysis of the by-products formed by urea decomposition at about 150degC-200degC in a DBD, since it is well known that, depending on the temperature, urea decomposition by-products can be quite different. It was found that 0.25 g of urea used can be completely decomposed in several minutes at a constant input applied voltage of 9 kV (10 kHz). The main by-products are ammonia, isocyanic acid, and cyanuric acid. Moreover, it was found that dry and humid air showed no difference in the by-products formed. View full abstract»

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  • Destruction of Chlorodifluoromethane (\hbox {CHF}_{2} \hbox {Cl}) by Using Dielectric Barrier Discharge Plasma

    Page(s): 449 - 455
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    The destruction of chlorodifluoromethane (CHF2Cl) was studied in a nonthermal atmospheric pressure plasma reactor with a perforated dielectric barrier, which is capable of producing intense streamers without significant pressure drop across the reactor. The performance of the dielectric barrier discharge reactor was evaluated with the parameters including oxygen content, input power, feed-gas flow rate, and initial CHF2Cl concentration. It was found that the reactive species from N2 mainly contributed to the destruction of CHF2Cl rather than those from oxygen and that the destruction efficiency largely decreased as the oxygen content increased. The change in the initial concentration did not nearly affect the destruction efficiency, which can partly be explained by the secondary destruction mechanism. The principle byproducts were identified using Fourier transform infrared spectroscopy, and chemical mechanisms were proposed for the destruction processes. According to the proposed mechanisms, COF2 was found to act as the key intermediate destruction product to convert CHF2Cl into CO2 and CO. View full abstract»

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  • A High-Density Hydrogen-Based Capillary Plasma Source for Particle-Beam-Driven Wakefield Accelerator Applications

    Page(s): 456 - 462
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    We report the generation of variable plasma densities up to 1019 cm-3 in hydrogen-filled hollow cathode capillary discharges and consider their applications as a practical plasma source for particle-beam-driven plasma wakefield accelerators. The capillary consists of a transparent cylindrical borosilicate glass tube. The plasma density is determined as a function of time, using Stark broadening of the Halpha line, with a resolution of 50 ns, and is found to decay exponentially with a typical time constant of several hundreds of nanoseconds. The time delay between the discharge and the drive electron beam can therefore be tuned to reach the density appropriate for the maximum acceleration gradient. The dependence of the plasma density on the capillary geometry and gas pressure is discussed, and the results of optical studies of the discharge channel formation process are presented. The implications of the results for beam-driven plasma accelerators araree discussed. View full abstract»

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  • Ferromagnetic Material Effects on Air Arc Behavior

    Page(s): 463 - 469
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    This paper is devoted to study the influence of ferromagnetic material on arc behavior in low voltage electric apparatus. With the self-programmed interface, one 2-D magnetohydrodynamic arc model can be developed based on the commercial software FLUENT and ANSYS, to study the vapor of ferromagnetic material effects on air arc behavior. Then, the corresponding interruption experiments are performed to verify the simulation qualitatively. It demonstrates that the vapor of ferromagnetic material is disadvantageous to arc interruption characteristics. In addition, the influence of the size of the ferromagnetic splitter plate on arc motion is simulated. It shows that the bigger splitter plate may accelerate the arc motion. View full abstract»

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  • Corrections to “Off-Axis Space-Charge Limit for a Bunched Electron Beam in a Coaxial Conducting Structure” [Jun 08 729-734]

    Page(s): 470
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    We discuss a correction to the Green's function used to calculate the off-axis space charge limit of bunched annular electron beams in coaxial conducting structures. In addition, we discuss how the space-charge limit is affected and update our previous comparison of the experimental design parameters of the UC-Davis/SLAC 2.8-GHz coaxial ubitron oscillator with the space-charge limit. View full abstract»

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    Page(s): 471
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    Page(s): 472
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  • IEEE Transactions on Plasma Science information for authors

    Page(s): C3
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  • Affiliate Plan of the IEEE Nuclear and Plasma Sciences Society

    Page(s): C4
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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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