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Plasma Science, IEEE Transactions on

Issue 2 • Date Apr 2001

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Displaying Results 1 - 14 of 14
  • A periodic table of ion charge-state distributions observed in the transition region between vacuum sparks and vacuum arcs

    Page(s): 393 - 398
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    Ion charge-state distributions have been measured with high time resolution for short (20 μs) and long (250 μs) vacuum discharges of 300 A. Charge-state data for 3 μs after discharge ignition and quasi-steady-state values are given for most conductive elements in a Periodic Table, including data for a few elements (rhodium, europium, and terbium) that were never before reported in the literature. Ion charge states are significantly higher at the beginning of the discharge and decay to their quasi-steady-state arc plasma values. It was found that the mean ion charge states can be fitted by functions of the form Q¯=Q¯t→∞ [1+A exp(-t/τ)] where A is an enhancement function that depends on the power density. For the present conditions, A~1 and τ~50 μs View full abstract»

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  • The efficiency of radicals production by positive streamer in air: the role of Laplacian field

    Page(s): 313 - 317
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (112 KB) |  | HTML iconHTML  

    Two-dimensional modeling of positive streamer in the air between a point anode and a plane cathode is performed. A number of radicals (excited molecules and atoms) produced by a streamer is calculated. The streamers near sharp and dull anodes are simulated. The sharp anode has five times smaller radius of tip curvature, and three times higher Laplacian field at the tip than the dull one. The results show that near the sharp anode, the streamer produces radicals ten times faster and at lower energy cost than near the dull anode. The mean energy cost of one radical is 10 eV View full abstract»

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  • High-voltage test of feedthroughs for a high-power ICRF antenna

    Page(s): 318 - 325
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB) |  | HTML iconHTML  

    A feedthrough is one of the most important parts of an ion cyclotron range of frequencies antenna for plasma heating in nuclear fusion devices. It must transmit RF power while keeping the antenna in high vacuum, and support antenna elements against electromagnetic forces and thermal stress. The standoff voltage, a key property for high-power transmission, is experimentally studied for six different types of feedthroughs. The Princeton Plasma Physics Laboratory (PPPL), Massachusetts Institute of Technology (MIT), Japan Atomic Energy Research Institute and Oak Ridge National Laboratory types show a standoff voltage of 40-52 kV with the pulse length 1 s, which indicates the possibility of power injection 1-1.6 MW in the present 50-Ω systems. If a 30-Ω feedthrough designed for the International Thermonuclear Experimental Reactor antenna, has a similar standoff voltage, 3-4 MW can be injected. Here, the antenna loading resistance is assumed as 3 Ω. In particular, the PPPL and MIT types show higher standoff voltages, which is inferred to be due to the design of the base flange covering the ceramic end. Multipactoring is observed in the voltage range less than 0.9-1.6 kV as predicted, but it is not a crucial problem. Therefore, a key point in designing a high-voltage standoff feedthrough is the optimization of the base flange and the ceramic ends View full abstract»

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  • Three-dimensional simulation on performance of a nonequilibrium disk MHD generator under subsonic flow condition

    Page(s): 335 - 340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    The performance of a nonequilibrium disk magnetohydrodynamic (MHD) generator under subsonic flow condition is examined with time-dependent τ-θ-z three-dimensional numerical simulation for the first time. The uniform plasma structure and proper fluid flow are realized for the optimal working condition. For low-load resistance, however, the flow chokes at the throat, and shock waves and boundary layer separation are observed in the generator channel. For high-load resistance, on the other hand, the subsonic flow is maintained, although the boundary layer becomes considerably thick. When the plasma with low electron temperature flows into the generator, ionization instability takes place, which markedly reduces the enthalpy extraction ratio and isentropic efficiency. This suggests that some way to raise the electron temperature in the upstream region, for example, a pre-ionization, is needed View full abstract»

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  • Responses of a long-coil pulse-modulated induction plasma

    Page(s): 326 - 334
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    Radio-frequency inductively coupled plasma in a pulse modulated approach was generated by a MOSFET inverter supply of high electric efficiency. The plasma torch has an extremely long coil region of 153 mm, which is an attractive feature for advanced materials processing, especially for better and more efficient vaporizing of solids. The operating conditions were: argon flow of 80 or 90 L/m at atmospheric pressure; supply power of 30 kW; and pulse on-time of 10 ms at 67% duty factor. Spectroscopic measurements were carried out to determine the temporal plasma properties, including the effects of shimmer current level (SCL) upon the spectral intensities. Additionally a time-dependent two-dimensional numerical model was solved for the same operating conditions employed in the experiment to predict and compare the plasma properties. Pulsed plasma dissipation sustained for a minimum SCL of 43% for 80 L/m gas flow-rate, and at any level below 43%, the plasma disappeared. Temporal variation of argon line intensities at 751 and 763.5 nm is similar, though the upper level intensity of the former one was significantly stronger than the latter. Intensified change of intensity is found at lower SCL because of higher change in the coil current and, in turn, in the plasma power. The predicted intensity of the 751-nm argon line showed similar behavior to the experimental intensity though the response around the instant of on-pulsation is somewhat slower View full abstract»

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  • Applicability of the hydrodynamic approximation to current-carrying plasma jets during their radial expansion

    Page(s): 371 - 376
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB) |  | HTML iconHTML  

    Supersonic spherically symmetric vacuum-arc plasma jets are considered using a two-liquid model. The jet starts from a radial distance of 3×10-3 m from the cathode surface with a radial directed electric current of 50-1000 A. Joule heating of the electron component and heat transfer to the ion component were calculated. The spatial distribution of plasma density, velocity, and electron and ion temperatures were obtained by numerically solving the equations of conservation of mass, energy, and momentum. The mean free path for the ion-ion collisions and the Mach number for the ion component of the plasma jet were also calculated as a function of the radial distance. The Knudsen number (Kn) for the ion component of plasma was calculated as a criterion of applicability of the hydrodynamical approximation. It was found that if Kn≪1 at the starting radial distance, it remains much less than unity, in spite of the decrease in the plasma density during the radial plasma expansion View full abstract»

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  • Electronic excitation temperature profiles in an air microwave plasma torch

    Page(s): 399 - 406
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    A 0.9- to 1.5-kW 2.45-GHz atmospheric pressure air microwave plasma torch has been operated efficiently with less than 1% reflected power. The plasma is sustained in a 28-mm internal diameter fused quartz tube, which penetrates perpendicularly through the wide walls of a tapered and shorted WR-284 (72×17-mm cross section) waveguide. A study has been made of the effects of power and airflow on the electronic excitation temperature, Texc. Abel inversion of radial profile chord averaged Fe I emission lines in the 370-377-nm range have been used to obtain localized profile measurements of Texc inside the waveguide excitation region. In general, temperature profiles peak on axis with no evidence of a skin effect in the large diameter (10-mm full width at half maximum emission intensity) plasmas. A maximum central Texc of 6550 K±350 K is observed at an airflow rate of 28 Ipm. When maintaining a constant flow rate of 14 Ipm, a 55% increase in microwave power from 0.9 to 1.4 kW causes a ~100% increase in plasma volume without any noticeable effect on the central Texc value. At a constant microwave power of 1.4 kW, an increase in total flow rate from 11 to 28 Ipm decreases the volume of the plasma by ~25% and increases the central Texc by ~13%. The axially peaked temperature profiles are consistent with an electron density of ~1013 cm-3 View full abstract»

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  • Analytic formulas for current density profiles in small-orbit spiralling electron beams

    Page(s): 349 - 359
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    Analytic expressions for the current density as a function of radius in small-orbit, spiralling electron beams, including guiding center spread, are derived using probability theory. The expressions are valid for beams with a small spread in Larmor radius compared to the guiding center spread and a space charge depression below 10%, which are typical for beams produced by modern magnetron injection guns. The current density profile is shown to exhibit a number of functional forms, depending on the relative size of the spread in guiding center radii compared to the average Larmor radius. Several applications for the new expressions are explored, including the calculation of the thermal loading experienced by beam-intercepting metal objects, as well as the computation of average electron density per unit volume (used in predicting the growth of electrostatic cyclotron instabilities). The analytic results are extended, in the vicinity of the beam edges, to include the effects of Larmor radius spread. The edge expressions are employed to predict the amount of current intercepted by a tunnel that closely surrounds the beam, which can be useful in selecting radial clearances View full abstract»

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  • The improvement of discharge characteristics by the use of asymmetric pulse driving in an alternating current plasma display panel

    Page(s): 377 - 382
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    Asymmetric pulse driving was employed to enhance the luminance and luminous efficacy of an AC plasma display panel (PDP). We observed dependencies of operating voltages, luminance and luminous efficacy on the pulse off-time ratio in asymmetric pulse driving. The luminance and luminous efficacy of the ac PDP improved when it was operated with small pulse-off time ratios in the asymmetric pulse driving. The spectral and temporal emission characteristics of vacuum ultraviolet (VUV) were investigated to explain the improvements. The luminous efficacy and VUV emission increased with the decrease of pulse off-time ratio, and with the increase of gas pressure View full abstract»

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  • Improved cathode design for long-pulse MILO operation

    Page(s): 388 - 392
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB) |  | HTML iconHTML  

    An improved cathode design for a magnetically insulated transmission line oscillator (MILO) has resulted in extending the radiated microwave pulse duration from 200 ns to over 400 ns. This was accomplished by maximizing the emission uniformity in the launch-point region of the cathode which, in turn, minimized anode plasma formation. The extended RF pulse duration has allowed us to find evidence of a new pulse-shortening mechanism late in the beam pulse: anode plasma formation in the load region View full abstract»

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  • The temperature measurement of the electrothermal-chemical launcher plasma by atomic emission spectroscopy

    Page(s): 360 - 364
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    The temperatures of electrothermal-chemical launcher plasmas of different capillary sizes and discharge conditions have been measured by atomic emission spectroscopy. The six copper neutral atomic lines of 510.554, 515.324. 521.820, 529.250, 570.020, and 578.213 mm were used. The measured temperatures are between 5670.0 (0.49 eV) and 8230.4 K (0.71 eV). In addition, the effect of the spectroscopic parameters of copper lines, such as the transition probability (A), the statistical weight of the upper level (g), and the energy of the upper level (Ei), on the calculated Bolzmann temperature has been discussed in detail. The results showed, however, that the Boltzmann function has a better linear correlation coefficient, the experimental results have higher reliability, and the accurate measurement of the plasma temperature can be obtained only when the spectroscopic parameters are selected correctly View full abstract»

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  • FDTD and PSTD simulations for plasma applications

    Page(s): 341 - 348
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB) |  | HTML iconHTML  

    Three-dimensional finite-difference time domain (FDTD) and pseudospectral time-domain (PSTD) algorithms, with perfectly matched layer absorbing boundary condition, are presented for nonmagnetized plasma as a special case of general inhomogeneous, dispersive, conductive media. The algorithms are tested for three typical frequency bands, and an excellent agreement between the FDTD/PSTD numerical results and analytical solutions is obtained for all cases. Several applications, such as laser-pulse propagation in plasma hollow channels, surface-wave propagation along a plasma column of finite length, and energy deposition of electron cyclotron resonance plasma source, demonstrate the capability and effectiveness of these algorithms. The PSTD algorithm is more efficient and accurate than the FDTD algorithm, and is suitable for large-scale problems, while the FDTD algorithm is more suitable for fine details. The numerical results also show that plasma has complex transient responses, especially in the low-frequency and resonance regimes. Because of their flexibility and generality, the algorithms and computer programs can be used to simulate various electromagnetic waves-plasma interactions with complex geometry and medium properties, both in time and frequency domains View full abstract»

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  • A transmission line filled with fast switched periodic plasma as a wide-band frequency transformer

    Page(s): 365 - 370
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    An adiabatic theory is first presented to show the enhancing effects of a periodic structure and a magnetic field on wave frequency-shifting process by rapidly produced plasma. A device having a cylindrical coaxial line configuration and featuring with a periodic cusp magnetic field is then constructed to study the theoretically predicted time-domain wave phenomena. The magnetic field is introduced by ring-shaped permanent magnets installed outside the outer cylinder of the coax in an arrangement with alternating polarities. A rapid discharge by a rectangular voltage pulse between the center conductor and the outer cylinder of the coax generates periodically distributed plasma inside the coax. As an x-band test wave is introduced to propagate through the line, it is shown that the wave frequency is shifted both upward and downward by suddenly created periodically distributed plasma. The effectiveness of the magnetic field (periodic as well as uniform distribution) on broadening the power spectra of frequency-shifted waves is demonstrated by comparing the spectra for the magnetized cases with that for the unmagnetized case View full abstract»

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  • Plasma uniformity of inductively coupled plasma reactor with helical heating coil

    Page(s): 383 - 387
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    For a plasma reactor consisting of a reactor and an inductively coupled plasma source, a simple method to adjust the plasma uniformity of the reactor is proposed. The source has a helical resonator structure with a helical coil short-circuited at one end and open-circuited at the other end. To adjust the plasma uniformity, this method uses an RF tap which is located at the helical coil and feeds RF power into the plasma source. Depending on the location of the RF tap, the axial density profile at the source changes and that adjusts the plasma uniformity of the reactor. The achieved plasma uniformity within a diameter of 120 mm is less than ±2.5%. Effects of various process conditions on plasma uniformity are also examined. It is concluded that the proposed method has a great potential for uniformity adjustment in an advanced plasma processing system View full abstract»

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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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