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Sample records for cathodic current density

  1. High current density cathode for electrorefining in molten electrolyte

    Science.gov (United States)

    Li, Shelly X.

    2010-06-29

    A high current density cathode for electrorefining in a molten electrolyte for the continuous production and collection of loose dendritic or powdery deposits. The high current density cathode eliminates the requirement for mechanical scraping and electrochemical stripping of the deposits from the cathode in an anode/cathode module. The high current density cathode comprises a perforated electrical insulated material coating such that the current density is up to 3 A/cm.sup.2.

  2. High current density pulsed cathode experiments at SLAC

    International Nuclear Information System (INIS)

    A 1.9 microperveance beam diode has been constructed to test high current density cathodes for use in klystrons. Several standard and specially coated dispenser cathodes are being tested. Results of tests to date show average cathode current densities in excess of 25 amps/cm, and maximum electric field gradients of more than 450 kV/cm for pulses of the order of 1μsec. 3 refs., 11 figs

  3. Rf Gun with High-Current Density Field Emission Cathode

    International Nuclear Information System (INIS)

    High current-density field emission from an array of carbon nanotubes, with field-emission-transistor control, and with secondary electron channel multiplication in a ceramic facing structure, have been combined in a cold cathode for rf guns and diode guns. Electrodynamic and space-charge flow simulations were conducted to specify the cathode configuration and range of emission current density from the field emission cold cathode. Design of this cathode has been made for installation and testing in an existing S-band 2-1/2 cell rf gun. With emission control and modulation, and with current density in the range of 0.1-1 kA/cm2, this cathode could provide performance and long-life not enjoyed by other currently-available cathodes

  4. High current density nanofilament cathodes for microwave amplifiers

    NARCIS (Netherlands)

    Schnell, J-P.; Minoux, E.; Gangloff, L.; Vincent, P.; Legagneux, P.; Dieumegard, D.; David, J.-F.; Peauger, F.; Hudanski, L.; Teo, K.B.K.; Lacerda, R.; Chhowalla, M.; Hasko, D.G.; Ahmed, H.; Amaratunga, G.A.J.; Milne, W.I.; Vila, L.; Dauginet-De Pra, L.; Demoustier-Champagne, S.; Ferain, E.; Legras, R.; Piraux, L.; Gröening, O.; Raedt, H. De; Michielsen, K.

    2004-01-01

    We study high current density nanofilament cathodes for microwave amplifiers. Two different types of aligned nanofilament array have been studied: first, metallic nanowires grown by electrodeposition into nanoporous templates at very low temperature (T

  5. Radial profiles of electron density and current components at cathode surface in LaB6 hollow cathode arc

    International Nuclear Information System (INIS)

    Experimental studies on a hydrogen-fed LaB6 hollow cathode arc have been pursued. The plasma parameter in the cathode has been measured by a Langmuir probe. The radial variation in the electron density inside the cathode was calculated using the continuity and momentum equations, showing good agreement with the experimental results. The electron density at the cathode surface was estimated to be 15 % - 20 % of that at the cathode axis. It was also found from the current balance that the arc current components at the cathode surface consist of a thermionic current which takes into account the Schottky effect, the ion current and the secondary electron current induced by ion bombardment. The ion current and the cathode surface is larger than the electron current emitted from the cathode. (author)

  6. High Current Density, Long Life Cathodes for High Power RF Sources

    Energy Technology Data Exchange (ETDEWEB)

    Ives, Robert Lawrence [Calabazas Creek Research,, Inc.; Collins, George [Calabazas Creek Research, Inc.; Falce, Lou [Consultant; Schwartzkopf, Steve [Ron Witherspoon, Inc.; Busbaher, Daniel [Semicon Associates

    2014-01-22

    This program was tasked with improving the quality and expanding applications for Controlled Porosity Reservoir (CPR) cathodes. Calabazas Creek Research, Inc. (CCR) initially developed CPR cathodes on a DOE-funded SBIR program to improve cathodes for magnetron injection guns. Subsequent funding was received from the Defense Advanced Research Projects Agency. The program developed design requirements for implementation of the technology into high current density cathodes for high frequency applications. During Phase I of this program, CCR was awarded the prestigious 2011 R&D100 award for this technology. Subsequently, the technology was presented at numerous technical conferences. A patent was issued for the technology in 2009. These cathodes are now marketed by Semicon Associates, Inc. in Lexington, KY. They are the world’s largest producer of cathodes for vacuum electron devices. During this program, CCR teamed with Semicon Associates, Inc. and Ron Witherspoon, Inc. to improve the fabrication processes and expand applications for the cathodes. Specific fabrications issues included the quality of the wire winding that provides the basic structure and the sintering to bond the wires into a robust, cohesive structure. The program also developed improved techniques for integrating the resulting material into cathodes for electron guns.

  7. High-brightness, high-current-density cathode for induction linac FELs

    International Nuclear Information System (INIS)

    The authors have recently initiated an investigation to determine the intrinsic operating limits of an osmium coated dispenser cathode for use in free-electron lasers (FELs) driven by an induction linear accelerator. The experimental apparatus consists of a 5.1-cm-diam osmium coated dispenser cathode driven by a 250-kV, 10-Ω, 35-ns Blumlein pulse line. The pepper pot technique is used to measure intrinsic cathode brightness and uniformity. Recent measurements have yielded brightness values exceeding 1 x 1010 A/m2rad2 for current densities up to 140 A/cm2. They have also obtained quantitative data on cathode poisoning caused by a number of chemical agents of interest in the induction linac environment. 7 refs., 8 figs., 2 tabs

  8. High-current density, high-brightness electron beams from large-area lanthanum hexaboride cathodes

    Science.gov (United States)

    Loschialpo, P.; Kapetanakos, C. A.

    1988-04-01

    Large diameter lanthanum hexaboride (LaB6) cathodes operated at 10 kV have produced 1-5-microsec electron pulses with current density between 10 and 20 A/sq cm. Normalized beam brightness, approximately 300,000 A/sq cm sq rad has been consistently measured. To obtain this high-current density, the LaB6 cathodes have been heated to temperatures between about 1600 and 1800 C. Very uniform temperature profiles are obtained by applying a carefully tailored electron bombardment heating power distribution. These measurements have been made between pressure 10 to the -6th to -10 to the -5th Torr, i.e., under much less demanding vacuum conditions than that required by conventional dispenser-type cathodes.

  9. High-current density, high-brightness electron beams from large-area lanthanum hexaboride cathodes

    International Nuclear Information System (INIS)

    Large (∼5 cm) diameter lanthanum hexaboride (LaB6) cathodes operated at 10 kV have produced 1--5-μs electron pulses with current density between 10 and 20 A/cm2. Normalized beam brightness, B/sub n/ = I/(πβγε)2, approximately 3 x 105 A/cm2 rad2 has been consistently measured. To obtain this high-current density, the LaB6 cathodes have been heated to temperatures between ∼1600 and 1800 0C. Very uniform temperature profiles are obtained by applying a carefully tailored electron bombardment heating power distribution. These measurements have been made between pressure 10-6--10-5 Torr, i.e., under much less demanding vacuum conditions than that required by conventional dispenser-type cathodes

  10. Current densities and closure rates in diodes containing laser-driven, cesium-coated thermionic cathodes

    Science.gov (United States)

    Lee, C.; Oettinger, P. E.

    1985-09-01

    Cathodes emitting electron current pulses of 100-1,000 A/sq cm for durations of longer than 1 microsecond, with very low emittance, are desirable for free electron laser and high-power microwave tube applications. Not all of these criteria can be satisfied by either dispenser thermionic cathodes or plasma forming field emitters. However, pulse-laser heated smooth cesiated refractory metal surfaces have the potential to achieve these conditions. In this paper, test results from low-voltage (2-20 kV) diodes containing cesiated tungsten cathodes are discussed. Space-charge-limited current densities of up to 30 A/sq cm were obtained in fields with maximum strengths of 40 kV/cm. Plasma closure rates at these currents were measured to be 0.17-0.4 cm/microsecond. Such slow velocity fronts are postulated to be due to the domination of the plasma by massive cesium ions generated from species desorbed from the cathode, rather than to light hydrogen ions (as in the case of field-emission-type cathodes).

  11. Current densities and closure rates in diodes containing laser-driven, cesium-coated thermionic cathodes

    International Nuclear Information System (INIS)

    Cathodes emitting electron current pulses of 102--103 A/cm2 for durations of longer than 1 μs, with very low emittance, are desirable for free electron laser and high-power microwave tube applications. Not all of these criteria can be satisfied by either dispenser thermionic cathodes or plasma forming field emitters. However, pulse-laser heated smooth cesiated refractory metal surfaces have the potential to achieve these conditions. In this paper, test results from low-voltage (2--20 kV) diodes containing cesiated tungsten cathodes are discussed. Space-charge-limited current densities of up to 30 A/cm2 were obtained in fields with maximum strengths of 40 kV/cm. Plasma closure rates at these currents were measured to be 0.17--0.4 cm/μs. Such slow velocity fronts are postualted to be due to the domination of the plasma by massive cesium ions generated from species desorbed from the cathode, rather than to light hydrogen ions (as in the case of field-emission-type cathodes)

  12. A carbon nanotube field emission cathode with high current density and long-term stability

    Energy Technology Data Exchange (ETDEWEB)

    Calderon-Colon, Xiomara; Zhou, Otto [Curriculum in Applied Science and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 (United States); Geng Huaizhi; Gao Bo [Xintek, Incorporated, 7020 Kit Creek Road, Research Triangle Park, NC (United States); An Lei; Cao Guohua [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 (United States)

    2009-08-12

    Carbon nanotube (CNT) field emitters are now being evaluated for a wide range of vacuum electronic applications. However, problems including short lifetime at high current density, instability under high voltage, poor emission uniformity, and pixel-to-pixel inconsistency are still major obstacles for device applications. We developed an electrophoretic process to fabricate composite CNT films with controlled nanotube orientation and surface density, and enhanced adhesion. The cathodes have significantly enhanced macroscopic field emission current density and long-term stability under high operating voltages. The application of this CNT electron source for high-resolution x-ray imaging is demonstrated.

  13. Current density at the refractory cathode of a high-current high-pressure arc (two modes of cathode spot attachment)

    Energy Technology Data Exchange (ETDEWEB)

    Nemchinsky, Valerian [ESAB Welding and Cutting Products and Francis Marion University, Florence, SC 29501 (United States)

    2003-12-07

    The attachment of a high-pressure arc at a refractory cathode was investigated theoretically and experimentally. Simple model considerations showed that an isolated cathode spot (CS) could function in two different modes. At relatively low currents and pressures, the CS mode (first mode) corresponds to the existing model (Bade W L and Yos Y M 1963 Technical Documentary Report No ASD-TDR-62-729 vol 1 (part II); Neumann W 1969 Beitr Plasmaphysik 9 499-526; Benilov M S 1993 Phys. Rev. 48 506-15, 1994 IEEE Trans. Plasma Sci. 22 73-7, 1999 J. Phys. D: Appl. Phys. 32 257-62; Benilov M S and Marotta A 1995 J. Phys. D: Appl. Phys. 28 1869-82; Benilov M S and Cunha M D 2002 J. Phys. D: Appl. Phys. 35 1736-50, 2003 J. Phys. D: Appl. Phys. 36 603-14). In this mode current density does not depend on the arc current and is directly proportional to the gas pressure. At higher currents and/or higher pressures the CS exists in a different mode (second mode). In this mode current density does not depend on pressure and decreases as the current increases. If the product of the arc current, I, and the gas pressure, p, is lower than some critical value, then the first mode is realized; at a higher Ip product, the second one is realized. For discharges in nitrogen, the critical value was estimated as {approx}7 x 10{sup 7} A Pa. In the experimental part of this work, we investigated the footprints that the arc left at the cathode after it was terminated. Cathodes were made of pure and thoriated tungsten and the gases were nitrogen and argon. We have observed both modes. At 3 x 10{sup 5} Pa, the second mode was observed at currents higher than {approx}300 A; at 200 A, it was observed at pressures higher than {approx}3 x 10{sup 5} Pa. The CS footprint appearances are quite different. In the first mode the footprint has a smooth central part and a heavily eroded periphery. We believe that the cathode temperature is maximal not at the CS centre but at its periphery in this mode. With a

  14. Current densities and closure rates in diodes containing laser driven, cesium-coated thermionic cathodes

    International Nuclear Information System (INIS)

    Although free electron laser oscillators have now been observed to lase from the visible into the microwave regions of the spectrum, the efficiency of coupling the electron beam energy to the radiative field is very low. In order to enhance this energy transfer, it is especially important to raise the current density and lower the emittance of the beam propagating down the accelerator. Of secondary interest is the elongation of the pulse length of the emitted radiation for those applications where relatively large values of this variable are desirable. Cathodes emitting 10/sub 2/ to 10/sub 3/ A/cm/sub 2/ for durations of 1 μs, with very low emittance are desirable. All of these criteria cannot be satisfied by either dispenser thermionic cathodes or plasma forming field emitters. However, laser-driven smooth cesiated surfaces have the potential to achieve these conditions. During the past year, space charge-limited current densities of up to 30 A/cm/sup 2/ with rise times under 40 ns have been generated in fields with maximum strengths of 40 kV/cm

  15. Power-Efficient, High-Current-Density, Long-Life Thermionic Cathode Developed for Microwave Amplifier Applications

    Science.gov (United States)

    Wintucky, Edwin G.

    2002-01-01

    A power-efficient, miniature, easily manufactured, reservoir-type barium-dispenser thermionic cathode has been developed that offers the significant advantages of simultaneous high electron-emission current density (>2 A/sq cm) and very long life (>100,000 hr of continuous operation) when compared with the commonly used impregnated-type barium-dispenser cathodes. Important applications of this cathode are a wide variety of microwave and millimeter-wave vacuum electronic devices, where high output power and reliability (long life) are essential. We also expect it to enable the practical development of higher purveyance electron guns for lower voltage and more reliable device operation. The low cathode heater power and reduced size and mass are expected to be particularly beneficial in traveling-wave-tube amplifiers (TWTA's) for space communications, where future NASA mission requirements include smaller onboard spacecraft systems, higher data transmission rates (high frequency and output power) and greater electrical efficiency.

  16. High current density electron gun with a LaB6 thermionic cathode

    International Nuclear Information System (INIS)

    To develop a high current electron gun for the induction linac, a small prototype of a Pierce-type electron gun using a planar 12 mm-diameter lanthanum hexaboride as an electron emitter has been made. The basic properties of the gun are under investigation and preliminary results are presented. The gun has been operated up to 21kV, obtaining current of 5.5A with 250 nsec width at 1,650degC in the space-charge-limited region. The cathode is heated by electron bombardment and radiation from a tungsten heater. The maximum temperature of the cathode reaches 1,690degC when the total heating power comes up to 590W. (author)

  17. Low platinum, high limiting current density of the PEMFC (proton exchange membrane fuel cell) based on multilayer cathode catalyst approach

    International Nuclear Information System (INIS)

    Novel multilayer cathode electrodes structures for PEMFC (proton exchange membrane fuel cell) based on sputtering technique were developed to provide high performance with low loading Pt of 0.05 mg/cm² compared to the standard MEA (membrane electrode assembly) cathode (∼0.2–0.3 mg/cm²). Different configurations of cathode catalyst layer were made by altering Pt and CN (Carbon–Nafion) ink carefully prepared on gas diffusion layer containing MPL (micro porous layer). The performances of PEMFC containing the multilayer electrodes were compared based on their measured polarization curves. Higher limiting current densities were achieved compared to standard MEA with platinum loading of 0.2 mg/cm² both at the cathode and the anode sides. Limiting current densities over 1.1 A/cm2, 1.2 A/cm2 and 1.4 A/cm2 were reached whereas maximum powers were in the range of 500 mW/cm² at 600 mW/cm². The good performances obtained can be due to the structural improvement which has contributed to a better catalyst utilization compared to conventional methods. A CN loading inferior to 0.24 mg/cm² between each layer is preferred for multilayer electrode. - Highlights: • Multilayer cathode of PEM fuel cell. • Enhanced performances with carbon–Nafion layer of PEM fuel cell. • Effect of the number of Pt sputtered layers on cell performance. • Increased power densities achieved. • Increased limiting current densities achieved

  18. Influence of cathodic current density and mechanical stirring on the electrodeposition of Cu-Co alloys in citrate bath

    Directory of Open Access Journals (Sweden)

    Leandro Trinta de Farias

    2008-03-01

    Full Text Available Cathodic polarization curves of Cu-Co alloys were galvanostatically obtained on a platinum net, using electrolytes containing copper and cobalt sulfates, sodium citrate and boric acid (pH values ranging from 4.88 to 6.00, with different mechanical stirring conditions. In order to evaluate quantitatively the influence of the applied current density and the mechanical stirring on the cathodic efficiency, the alloy composition for the Cu-Co alloy deposition process, and the average deposition potential, an experimental central composite design 2² was employed, and three current density intervals (0.11 to 0.60, 0.50 to 1.98 and 2.44 to 9.94 mA.cm-2 were chosen from the polarization curves for this purpose. The results indicated that the current density (mainly in the range between 0.11 and 0.60 mA.cm-2 affected significantly all the studied variables. In the intermediate range (0.50 to 1.98 mA.cm-2, only the average potential was influenced by the current density. On the other hand, the mechanical stirring had a significant effect only on the copper content, for both the lowest (0.11 to 0.60 mA.cm-2 and the highest current density range (2.44 to 9.94 mA.cm-2. Indeed, in the last range, none of the studied deposition parameters presented significant influence on the studied variables, except for the copper content. This could probably be explained by the direct incorporation of Cu-Citrate complexes in the coating, which was enhanced at high current values.

  19. Influence of current density on the erosion of a graphite cathode and electrolytic formation of carbon nanotubes in molten NaCl and LiCl

    International Nuclear Information System (INIS)

    The electrochemical deposition of sodium and lithium from their respective molten chlorides onto a graphite cathode as the first step of carbon nanotube electrolytic production has been investigated. It has been shown that in the case of both sodium and lithium, as the cathodic current density increases, the cathode weight first increases and then decreases, i.e. the dependence of cathode weight change vs. cathodic current density passes through a maximum. The value of cathodic current density corresponding to the maximum increase in the cathode weight in the case of sodium is approximately 4 times as high as that in the case of lithium, which is explained by a higher solubility of sodium metal in molten sodium chloride compared to that of lithium metal in molten lithium chloride. The higher sodium metal solubility causes a higher electronic conductivity of the molten electrolyte, while the ratio of intercalated to dissolved sodium will be lower as compared to lithium. Curved multi-walled carbon nanotubes of an outer diameter of 20-50 nm with a wall thickness of 5-10 nm (molten NaCl) and of 20-100 nm with a wall thickness of 5-40 nm (molten LiCl) have been synthesized.

  20. Optimization of operating parameters to maximize the current density without flooding at the cathode membrane interface of a PEM fuel cell using Taguchi method and genetic algorithm

    Directory of Open Access Journals (Sweden)

    S.S.L. Rao, A. Shaija, S. Jayaraj

    2014-01-01

    Full Text Available A mathematical model was developed to investigate water accumulation at the cathode membrane interface by varying different operating parameters like fuel cell operating temperature and pressure, cathode and anode humidification temperatures and cathode stoichiometry. Taguchi optimization methodology is then combined with this model to determine the optimal combination of the operating parameters to maximize current density without flooding. Results of analysis of variance (ANOVA show that fuel cell operating temperature and cathode humidification temperature are the two most significant parameters in the ratio of 56.07% and 27.89% respectively and also that higher fuel cell temperature and lower cathode humidification temperature are favourable to get the maximum current draw without flooding at the cathode membrane interface. The global optimum value of the operating parameters to maximize the current density without flooding was obtained by formulating as an optimization problem using genetic algorithm (GA. These results were compared with the results obtained using Taguchi method and it was found to be similar and slightly better.

  1. Investigation of the liquid water distributions in a 50 cm2 PEM fuel cell: Effects of reactants relative humidity, current density, and cathode stoichiometry

    International Nuclear Information System (INIS)

    A 50 cm2 commercial PEM fuel cell has been used to investigate the effects of a set of different operating conditions on the resulting liquid water distributions in the cell. A comprehensive matrix of operating conditions was analyzed, varying the reactants relative humidity (anode and cathode), cathode stoichiometry, and cell current density. Neutron imaging was used to determine the liquid water distributions within the cell for each operating condition. The obtained neutron radiographs were post-processed and analyzed in order to assess the effects of the different operating conditions. Cell voltage and cell resistance (High Frequency Resistance) were also monitored during the experiments and included in the analysis. Overall, the well-known water distributions corresponding to serpentine flow fields were observed, featuring a progressive water accumulation along the gas flow and towards the outlet port. Cathode channels were showing water accumulation. It was found that the cathode relative humidity had a much larger effect on the cell water content and overall performance than the anode relative humidity for this particular cell. - Highlights: • Neutron radiographs were used to study the water distribution in a 50 cm2 PEMFC. • A matrix of relative humidity, current density, stoichiometry, was investigated. • Cathode RH was found to have a larger impact than anode RH for the MEA used (N117)

  2. Emission mechanism in high current hollow cathode arcs

    International Nuclear Information System (INIS)

    Large (2 cm-diameter) hollow cathodes have been operated in a magnetoplasmadynamic (MPD) arc over wide ranges of current (0.25 to 17 kA) and mass flow (10-3 to 8 g/sec), with orifice current densities and mass fluxes encompassing those encountered in low current steady-state hollow cathode arcs. Detailed cathode interior measurements of current and potential distributions show that maximum current penetration into the cathode is about one diameter axially upstream from the tip, with peak inner surface current attachment up to one cathode diameter upstream of the tip. The spontaneous attachment of peak current upstream of the cathode tip is suggested as a criterion for characteristic hollow cathode operation. This empirical criterion is verified by experiment

  3. Effect of cathodic current density on performance of tungsten coatings on molybdenum prepared by electrodeposition in molten salt

    Science.gov (United States)

    Jiang, Fan

    2016-02-01

    Smooth tungsten coatings were prepared at current density below 70 mA cm-2 by electrodeposition on molybdenum substrate from Na2WO4-WO3 -melt at 1173 K in air atmosphere. As the current density reached up to 90 mA cm-2, many significant nodules were observed on the surface of the coating. Surface characterization, microstructure and mechanical properties were performed on the tungsten coatings. As the increasing of current density, the preferred orientation of the coatings changed to (2 0 0). All coatings exhibited columnar-grained-crystalline. There was about a 2 μm thick diffusion layer between tungsten coating and molybdenum substrate. The bending test revealed the tungsten coating had -good bonding strength with the molybdenum substrate. There is a down trend of the grain size of the coating on molybdenum as the current density increased from 30 mA cm-2 to 50 mA cm-2. The coating obtained at 50 mA cm-2 had a minimum grain size of 4.57 μm, while the microhardness of this coating reached to a maximum value of 495 HV.

  4. The use of segmented cathodes to determine the spoke current density distribution in high power impulse magnetron sputtering plasmas

    Science.gov (United States)

    Poolcharuansin, Phitsanu; Estrin, Francis Lockwood; Bradley, James W.

    2015-04-01

    The localized target current density associated with quasi-periodic ionization zones (spokes) has been measured in a high power impulse magnetron sputtering (HiPIMS) discharge using an array of azimuthally separated and electrical isolated probes incorporated into a circular aluminum target. For a particular range of operating conditions (pulse energies up to 2.2 J and argon pressures from 0.2 to 1.9 Pa), strong oscillations in the probe current density are seen with amplitudes up to 52% above a base value. These perturbations, identified as spokes, travel around the discharge above the target in the E×B direction. Using phase information from the angularly separated probes, the spoke drift speeds, angular frequencies, and mode number have been determined. Generally, at low HiPIMS pulse energies Ep velocities between 6.5 and 10 km s-1 and mode numbers m = 3 or above. At Ep > 1.8 J, the plasma becomes spoke-free. The boundaries between chaotic, coherent, and no-spoke regions are weakly dependent on pressure. During each HiPIMS pulse, the spoke velocities increase by about 50%. Such an observation is explained by considering spoke velocities to be determined by the critical ionization velocity, which changes as the plasma composition changes during the pulse. From the shape of individual current density oscillations, it appears that the leading edge of the spoke is associated with a slow increase in local current density to the target and the rear with a more rapid decrease. The measurements show that the discharge current density associated with individual spokes is broadly spread over a wide region of the target.

  5. The use of segmented cathodes to determine the spoke current density distribution in high power impulse magnetron sputtering plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Poolcharuansin, Phitsanu [Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, Liverpool L69 3GJ (United Kingdom); The Technological Plasma Research Unit, Department of Physics, Mahasarakham University, Maha Sarakham 44150 (Thailand); Estrin, Francis Lockwood; Bradley, James W., E-mail: j.w.bradley@liverpool.ac.uk [Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, Liverpool L69 3GJ (United Kingdom)

    2015-04-28

    The localized target current density associated with quasi-periodic ionization zones (spokes) has been measured in a high power impulse magnetron sputtering (HiPIMS) discharge using an array of azimuthally separated and electrical isolated probes incorporated into a circular aluminum target. For a particular range of operating conditions (pulse energies up to 2.2 J and argon pressures from 0.2 to 1.9 Pa), strong oscillations in the probe current density are seen with amplitudes up to 52% above a base value. These perturbations, identified as spokes, travel around the discharge above the target in the E×B direction. Using phase information from the angularly separated probes, the spoke drift speeds, angular frequencies, and mode number have been determined. Generally, at low HiPIMS pulse energies E{sub p} < 0.8 J, spokes appear to be chaotic in nature (with random arrival times), however as E{sub p} increases, coherent spokes are observed with velocities between 6.5 and 10 km s{sup −1} and mode numbers m = 3 or above. At E{sub p} > 1.8 J, the plasma becomes spoke-free. The boundaries between chaotic, coherent, and no-spoke regions are weakly dependent on pressure. During each HiPIMS pulse, the spoke velocities increase by about 50%. Such an observation is explained by considering spoke velocities to be determined by the critical ionization velocity, which changes as the plasma composition changes during the pulse. From the shape of individual current density oscillations, it appears that the leading edge of the spoke is associated with a slow increase in local current density to the target and the rear with a more rapid decrease. The measurements show that the discharge current density associated with individual spokes is broadly spread over a wide region of the target.

  6. The use of segmented cathodes to determine the spoke current density distribution in high power impulse magnetron sputtering plasmas

    International Nuclear Information System (INIS)

    The localized target current density associated with quasi-periodic ionization zones (spokes) has been measured in a high power impulse magnetron sputtering (HiPIMS) discharge using an array of azimuthally separated and electrical isolated probes incorporated into a circular aluminum target. For a particular range of operating conditions (pulse energies up to 2.2 J and argon pressures from 0.2 to 1.9 Pa), strong oscillations in the probe current density are seen with amplitudes up to 52% above a base value. These perturbations, identified as spokes, travel around the discharge above the target in the E×B direction. Using phase information from the angularly separated probes, the spoke drift speeds, angular frequencies, and mode number have been determined. Generally, at low HiPIMS pulse energies Ep < 0.8 J, spokes appear to be chaotic in nature (with random arrival times), however as Ep increases, coherent spokes are observed with velocities between 6.5 and 10 km s−1 and mode numbers m = 3 or above. At Ep > 1.8 J, the plasma becomes spoke-free. The boundaries between chaotic, coherent, and no-spoke regions are weakly dependent on pressure. During each HiPIMS pulse, the spoke velocities increase by about 50%. Such an observation is explained by considering spoke velocities to be determined by the critical ionization velocity, which changes as the plasma composition changes during the pulse. From the shape of individual current density oscillations, it appears that the leading edge of the spoke is associated with a slow increase in local current density to the target and the rear with a more rapid decrease. The measurements show that the discharge current density associated with individual spokes is broadly spread over a wide region of the target

  7. Nano-scale investigations of electric-dipole-layer enhanced field and thermionic emission from high current density cathodes

    Science.gov (United States)

    Vlahos, Vasilios

    Cesium iodide coated graphitic fibers and scandate cathodes are two important electron emission technologies. The coated fibers are utilized as field emitters for high power microwave sources. The scandate cathodes are promising thermionic cathode materials for pulsed power vacuum electron devices. This work attempts to understand the fundamental physical and chemical relationships between the atomic structure of the emitting cathode surfaces and the superior emission characteristics of these cathodes. Ab initio computational modeling in conjunction with experimental investigations was performed on coated fiber cathodes to understand the origin of their very low turn on electric field, which can be reduced by as much as ten-fold compared to uncoated fibers. Copious amounts of cesium and oxygen were found co-localized on the fiber, but no iodine was detected on the surface. Additional ab initio studies confirmed that cesium oxide dimers could lower the work function significantly. Surface cesium oxide dipoles are therefore proposed as the source of the observed reduction in the turn on electric field. It is also proposed that emission may be further enhanced by secondary electrons from cesium oxide during operation. Thermal conditioning of the coated cathode may be a mechanism by which surface cesium iodide is converted into cesium oxide, promoting the depletion of iodine by formation of volatile gas. Ab initio modeling was also utilized to investigate the stability and work functions of scandate structures. The work demonstrated that monolayer barium-scandium-oxygen surface structures on tungsten can dramatically lower the work function of the underlying tungsten substrate from 4.6 eV down to 1.16 eV, by the formation of multiple surface dipoles. On the basis of this work, we conclude that high temperature kinetics force conventional dispenser cathodes (barium-oxygen monolayers on tungsten) to operate in a non-equilibrium compositional steady state with higher than

  8. High-current carbon-epoxy capillary cathode

    Science.gov (United States)

    Gleizer, J. Z.; Queller, T.; Bliokh, Yu.; Yatom, S.; Vekselman, V.; Krasik, Ya. E.; Bernshtam, V.

    2012-07-01

    The results of experiments on the reproducible generation of an electron beam having a high current density of up to 300 A/cm2 and a satisfactorily uniform cross-sectional distribution of current density in a ˜200 kV, ˜450 ns vacuum diode with a carbon-epoxy capillary cathode are presented. It was found that the source of the electrons is the plasma formed as a result of flashover inside the capillaries. It is shown that the plasma formation occurs at an electric field ≤15 kV/cm and that the cathode sustains thousands of pulses without degradation in its emission properties. Time- and space-resolved visible light observation and spectroscopy analyses were used to determine the cathode plasma's density, temperature, and expansion velocity. It was found that the density of the cathode plasma decreases rapidly in relation to the distance from the cathode. In addition, it was found that the main reason for the short-circuiting of the accelerating gap is the formation and expansion of the anode plasma. Finally, it was shown that when an external guiding magnetic field is present, the injection of the electron beam into the drift space with a current amplitude exceeding its critical value changes the radial distribution of the current density of the electron beam because the inner electrons are reflected from the virtual cathode.

  9. Salt taste inhibition by cathodal current

    OpenAIRE

    Hettinger, Thomas P.; Frank, Marion E.

    2009-01-01

    Effects of cathodal current, which draws cations away from the tongue and drives anions toward the tongue, depend on the ionic content of electrolytes through which the current is passed. To address the role of cations and anions in human salt tastes, cathodal currents of −40 to −80 µA were applied to human subjects’ tongues through supra-threshold salt solutions. The salts were sodium chloride, sodium bromide, potassium chloride, ammonium chloride, calcium chloride, sodium nitrate, sodium su...

  10. Emission current from a single micropoint of explosive emission cathode

    International Nuclear Information System (INIS)

    Explosive emission cathodes (EECs) are widely used due to their large current. There has been much research on the explosive electron emission mechanism demonstrating that a current density of 108–109 A/cm2 is necessary for a micropoint to explode in several nanoseconds and the micropoint size is in micron-scale according to the observation of the cathode surface. This paper, however, makes an effort to research the current density and the micropoint size in another way which considers the space charge screening effect. Our model demonstrates that the relativistic effect is insignificant for the micropoint emission due to the small size of the micropoint and uncovers that the micron-scale size is an intrinsic demand for the micropoint to reach a space charge limited current density of 108–109 A/cm2. Meanwhile, our analysis shows that as the voltage increases, the micropoint emission will turn from a field limited state to a space charge limited state, which makes the steady-state micropoint current density independent of the cathode work function and much less dependent on the electric field and the field enhancement factor than that predicted by the Fowler-Nordheim formula

  11. Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics.

    Science.gov (United States)

    Lopatin, I V; Akhmadeev, Yu H; Koval, N N

    2015-10-01

    The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. When the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8-12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa). PMID:26520947

  12. Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics

    International Nuclear Information System (INIS)

    The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. When the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8–12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa)

  13. Emission current control system for multiple hollow cathode devices

    Science.gov (United States)

    Beattie, John R. (Inventor); Hancock, Donald J. (Inventor)

    1988-01-01

    An emission current control system for balancing the individual emission currents from an array of hollow cathodes has current sensors for determining the current drawn by each cathode from a power supply. Each current sensor has an output signal which has a magnitude proportional to the current. The current sensor output signals are averaged, the average value so obtained being applied to a respective controller for controlling the flow of an ion source material through each cathode. Also applied to each controller are the respective sensor output signals for each cathode and a common reference signal. The flow of source material through each hollow cathode is thereby made proportional to the current drawn by that cathode, the average current drawn by all of the cathodes, and the reference signal. Thus, the emission current of each cathode is controlled such that each is made substantially equal to the emission current of each of the other cathodes. When utilized as a component of a multiple hollow cathode ion propulsion motor, the emission current control system of the invention provides for balancing the thrust of the motor about the thrust axis and also for preventing premature failure of a hollow cathode source due to operation above a maximum rated emission current.

  14. Space-charge-limited currents for cathodes with electric field enhanced geometry

    Science.gov (United States)

    Lai, Dingguo; Qiu, Mengtong; Xu, Qifu; Huang, Zhongliang

    2016-08-01

    This paper presents the approximate analytic solutions of current density for annulus and circle cathodes. The current densities of annulus and circle cathodes are derived approximately from first principles, which are in agreement with simulation results. The large scaling laws can predict current densities of high current vacuum diodes including annulus and circle cathodes in practical applications. In order to discuss the relationship between current density and electric field on cathode surface, the existing analytical solutions of currents for concentric cylinder and sphere diodes are fitted from existing solutions relating with electric field enhancement factors. It is found that the space-charge-limited current density for the cathode with electric-field enhanced geometry can be written in a general form of J = g(βE)2J0, where J0 is the classical (1D) Child-Langmuir current density, βE is the electric field enhancement factor, and g is the geometrical correction factor depending on the cathode geometry.

  15. Single crystal LaB6: a comparison with currently used thermionic cathodes for broad beam applications

    International Nuclear Information System (INIS)

    The use of single crystal LaB6 cathodes in microbeam applications has grown dramatically in the past few years, due to recognition of the high current density/low volatility characteristics of this material. We present here experimental results suggesting that advanced, single crystal LaB6 cathodes should also satisfy the requirements of broad beam applications, such as satellite-borne traveling wave tubes, where high current density, long lifetime and excellent stability and reproducibility are necessary. The most important parameters for cathode characterization are available emitted current density, material vaporization rate, lifetime and power consumption. Other important characteristics are activation procedure, resistance to poisoning by impurities, emission stability and emission uniformity across the cathode emitting surface. The current state of the art cathode type used in commercial devices is the impregnated dispenser cathode (IDC). The construction of such cathodes are outlined briefly, and their operating properties are discussed

  16. Large area dispenser cathode applied to high current linac

    International Nuclear Information System (INIS)

    The paper introduced a dispenser cathode (411 M) which was 55 mm in diameter. A 200 kV long pulsed power generator with 2 μs flattop based on Marx-PEN and system with heat and voltage insulation were built. A 52 A space charge limited current was gained, when the temperature was 1165 degree C and the filament current was 18 A on the cathode and the voltage of the pulse was 75 kV at the cathode test stand. Experimental results show that the current values are consistent with the numerical simulation. The experiment reveals that the deflated gas will influence the cathode emission ability. (authors)

  17. Heat flux at the refractory cathode of a high-current, high-pressure arc (two modes of cathode spot attachment)

    Energy Technology Data Exchange (ETDEWEB)

    Nemchinsky, Valerian [ESAB Welding and Cutting Products and Francis Marion University, Florence SC 29501 (United States)

    2004-04-07

    Calorimetric measurements of a refractory (pure and thoriated tungsten) cathode in a high-current (100-500 A) high-pressure (1-5 atm) arc in nitrogen were performed. The measurements confirmed the existence of a 'high-current' mode of cathode spot (CS) operation-the mode we observed by a footprint method in our work (2003 J. Phys. D: Appl. Phys. 36 3007). In this mode, the heat load of a cathode does not depend on the pressure and is directly proportional to the arc current as opposed to the 'low current' mode where it is inversely proportional to the square root of pressure and directly proportional to the square root of current. The current density at the cathode surface calculated from the measured heat flux to the cathode is approximately half of the current density obtained by a footprint method. Both densities exhibit the same current and pressure dependences. The radial distribution of the cathode temperature inside the CS is discussed. We hypothesize that the temperature has its maximum at the spot periphery. In the case of the thoriated tungsten cathode, this maximum may be so high that, at this location, the cathode is virtually thorium free.

  18. Visualizing Current-Dependent Morphology and Distribution of Discharge Products in Sodium-Oxygen Battery Cathodes.

    Science.gov (United States)

    Schröder, Daniel; Bender, Conrad L; Osenberg, Markus; Hilger, André; Manke, Ingo; Janek, Jürgen

    2016-01-01

    Synchrotron X-ray tomography and scanning electron microscopy were applied to elucidate the spatial distribution of discharge product (NaO2) in the carbon cathode of sodium-oxygen batteries. Various batteries were discharged galvanostatically and their cathodes were analyzed. We observe a particle density gradient along the cathode that scales with the current density applied. Besides, we show that the particle size and shape of discharge product strongly depend on current density, and on whether the particles are deposited close to the oxygen reservoir or near the separator. We correlate our findings to transport limitations for the supplied oxygen and gain crucial information for optimal operation of sodium-oxygen batteries. Our findings imply that for low current densities pore clogging might occur, and that for elevated current densities small high surface area particles with limited electric conductivity form; both phenomena can decrease the available discharge and charge capacity significantly. PMID:27068448

  19. Visualizing Current-Dependent Morphology and Distribution of Discharge Products in Sodium-Oxygen Battery Cathodes

    Science.gov (United States)

    Schröder, Daniel; Bender, Conrad L.; Osenberg, Markus; Hilger, André; Manke, Ingo; Janek, Jürgen

    2016-04-01

    Synchrotron X-ray tomography and scanning electron microscopy were applied to elucidate the spatial distribution of discharge product (NaO2) in the carbon cathode of sodium-oxygen batteries. Various batteries were discharged galvanostatically and their cathodes were analyzed. We observe a particle density gradient along the cathode that scales with the current density applied. Besides, we show that the particle size and shape of discharge product strongly depend on current density, and on whether the particles are deposited close to the oxygen reservoir or near the separator. We correlate our findings to transport limitations for the supplied oxygen and gain crucial information for optimal operation of sodium-oxygen batteries. Our findings imply that for low current densities pore clogging might occur, and that for elevated current densities small high surface area particles with limited electric conductivity form; both phenomena can decrease the available discharge and charge capacity significantly.

  20. Analysis of cathode geometry to minimize cathode erosion in direct current microplasma jet

    Energy Technology Data Exchange (ETDEWEB)

    Causa, Federica [Dipartimento di Scienze dell' Ambiente, della Sicurezza, del Territorio, degli Alimenti e della Salute, Universita degli studi di Messina, 98122 Messina (Italy); Ghezzi, Francesco; Caniello, Roberto; Grosso, Giovanni [Istituto di Fisica del Plasma, Consiglio Nazionale delle Ricerche, EURATOM-ENEA-CNR Association, Via R. Cozzi 53, 20125 Milano (Italy); Dellasega, David [Istituto di Fisica del Plasma, Consiglio Nazionale delle Ricerche, EURATOM-ENEA-CNR Association, Via R. Cozzi 53, 20125 Milano (Italy); Dipartimento di Energia, Politecnico di Milano, Via Ponzio 34/3, 20133 Milano (Italy)

    2012-12-15

    Microplasma jets are now widely used for deposition, etching, and materials processing. The present study focuses on the investigation of the influence of cathode geometry on deposition quality, for microplasma jet deposition systems in low vacuum. The interest here is understanding the influence of hydrogen on sputtering and/or evaporation of the electrodes. Samples obtained with two cathode geometries with tapered and rectangular cross-sections have been investigated experimentally by scanning electron microscopy and energy dispersion X-ray spectroscopy. Samples obtained with a tapered-geometry cathode present heavy contamination, demonstrating cathode erosion, while samples obtained with a rectangular-cross-section cathode are free from contamination. These experimental characteristics were explained by modelling results showing a larger radial component of the electric field at the cathode inner wall of the tapered cathode. As a result, ion acceleration is larger, explaining the observed cathode erosion in this case. Results from the present investigation also show that the ratio of radial to axial field components is larger for the rectangular geometry case, thus, qualitatively explaining the presence of micro-hollow cathode discharge over a wide range of currents observed in this case. In the light of the above findings, the rectangular cathode geometry is considered to be more effective to achieve cleaner deposition.

  1. Physics of Plasma Cathode Current Injection During LHI

    Science.gov (United States)

    Hinson, E. T.; Barr, J.; Bongard, M.; Burke, M. G.; Fonck, R.; Perry, J.

    2015-11-01

    Localized helicity injection (LHI) ST startup employs current sources at the tokamak edge. Max Ip in LHI scales with injection voltage Vinj, requiring an understanding of injector impedance. For the arc-plasma cathode electron injectors in Pegasus, impedance is plasma-determined, and typically Vinj>1kV for Iinj = 2kA. At low Iinj, Iinj Vinj3 / 2 , an indication of a double layer (DL) common to such devices. However, at Iinj> 1kA, Iinj Vinj1 / 2 occurs, a scaling expected for limited launched beam density, nb ≡Iinj / (e√{ 2eVinj /me }Ainj) Iinj /Vinj1 / 2 . An ohmic discharge injection target was created to test this hypothesis. Langmuir probe data showed Iinj/Vinj1 / 2 nedge at low nedge, consistent with a limit (nedge >=ne , b) imposed by quasineutrality. If edge fueling maintained nedge >=ne , b , spectroscopic measurements of source density narc indicated Iinj/Vinj1 / 2 narc , as expected from DL expansion. Thus nb established by narc or nedge determines Vinj up to the onset of cathode spot (CS) arcing. Technology development has increased obtainable Vinj and reduced CS damage using new ring shielding and a cathode design drawing CS's away from insulators. This involved a novel optimization of conical frustum geometry. Finally, consistent with NIMROD predictions of coherent streams in the edge during LHI, pairwise triangulation of outboard Mirnov data assuming beam m =1 motion has allowed an estimate of beam R(t), Z(t) location that is near the injector R, and consistent across the array. Supported by U.S. DOE Grant DE-FG02-96ER54375.

  2. Current crowding effects in a CdS/LaS cold cathode

    International Nuclear Information System (INIS)

    We analyze the importance of current crowding in a new cold cathode emitter that consists of a thin wide band-gap semiconductor material sandwiched between a metallic contact and a low work function semimetallic thin film. Potential material candidates are suggested to achieve low-voltage (2. We calculate the lateral potential drop that occurs across the emission window of cold cathodes with rectangular geometry and describe its effects on the emitted current density profile. The power dissipation in the cold cathode is calculated as a function of a dimensionless parameter characterizing the importance of current crowding. We determine the range of dc bias over which cold cathodes of different width must be operated to minimize current crowding effects. copyright 1997 American Institute of Physics

  3. Os-coated cathode for very high emission-density applications

    Science.gov (United States)

    Shih, Arnold; Berry, Alan; Marrian, Christie R. K.; Haas, George A.

    1987-05-01

    Emission densities of 35 to 100 A/sq cm, demanded by free-electron lasers (FELs), have set far more stringent requirements on thermionic cathodes than what is considered state of the art with current technology. The purpose of the work considered here is to evaluate Os-coated cathodes for these ultrahigh-current-density applications. Organometallic CVD techniques were used to coat 'B' type tungsten dispenser cathodes. The coatings were found to show good adhesion and rapid activation. The activation process involves not only the standard formation of a BaO layer on the surface but also the formation of an optimum surface alloy composition of near 50-percent Os and 50-percent W. These cathodes showed excellent emission capabilities, and at a brightness temperature of 1085 C, a zero-field emission density near 50 A/sq cm was obtained. Subsequent life studies at a brightness temperature of 1085 C indicated that at an emission level of 40-50 A/sq cm over 800 h of life is obtainable with this type of cathode. During life, the pulsed emission density and surface composition were monitored. Surface Ba/BaO coverage as well as surface Os content were observed to decrease with life, but an S impurity was found to increase with life. However, the surface alloy composition change was identified as being the major cause for the emission degradation.

  4. A Robust High Current Density Electron Gun

    Science.gov (United States)

    Mako, F.; Peter, W.; Shiloh, J.; Len, L. K.

    1996-11-01

    Proof-of-principle experiments are proposed to validate a new concept for a robust, high-current density Pierce electron gun (RPG) for use in klystrons and high brightness electron sources for accelerators. This rugged, long-life electron gun avoids the difficulties associated with plasma cathodes, thermionic emitters, and field emission cathodes. The RPG concept employs the emission of secondary electrons in a transmission mode as opposed to the conventional mode of reflection, i.e., electrons exit from the back face of a thin negative electron affinity (NEA) material, and in the same direction as the incident beam. Current amplification through one stage of a NEA material could be over 50 times. The amplification is accomplished in one or more stages consisting of one primary emitter and one or more secondary emitters. The primary emitter is a low current density robust emitter (e.g., thoriated tungsten). The secondary emitters are thin NEA electrodes which emit secondary electrons in the same direction as the incident beam. Specific application is targeted for a klystron gun to be used by SLAC with a cold cathode at 30-40 amps/cm^2 output from the secondary emission stage, a ~2 μs pulse length, and ~200 pulses/second.

  5. THE CURRENT EFFICIENCY FOR ALUMINIUM DEPOSITION FROM CRYOLITEALUMINAMELTS AT HIGH CURRENT DENSITY

    OpenAIRE

    Armoo, Joseph Prince

    2010-01-01

    A laboratory study was performed to investigate first and foremost the effects of cathodic current density on the current efficiency with respect to aluminium electrolysis in cryolite-aluminamelts. Effects of NaF/AlF3 ratio and impurity concentration on CE were also investigated at a high current density of 1.5A/cm2.The laboratory cell used in the present study has been designed specifically to ensure evenly distributed current density on the aluminium cathode surface and to ensure good and r...

  6. Robust, easily shaped, and epoxy-free carbon-fiber-aluminum cathodes for generating high-current electron beams

    Science.gov (United States)

    Liu, Lie; Li, Limin; Wen, Jianchun; Wan, Hong

    2009-02-01

    This paper presents the construction of carbon-fiber-aluminum (CFA) cathode by squeezing casting and its applications for generating high-current electron beams to drive high-power microwave sources. The fabrication process avoided using epoxy, a volatile deteriorating the vacuum system. These cathodes had a higher hardness than conventional aluminum, facilitating machining. After surface treatment, carbon fibers became the dominator determining emission property. A multineedle CFA cathode was utilized in a triode virtual cathode oscillator (vircator), powered by a ˜450 kV, ˜400 ns pulse. It was found that 300-400 MW, ˜250 ns microwave was radiated at a dominant frequency of 2.6 GHz. Further, this cathode can endure high-current-density emission without detectable degradation in performance as the pulse shot proceeded, showing the robust nature of carbon fibers as explosive emitters. Overall, this new class of cold cathodes offers a potential prospect of developing high-current electron beam sources.

  7. Mesh optimization for microbial fuel cell cathodes constructed around stainless steel mesh current collectors

    KAUST Repository

    Zhang, Fang

    2011-02-01

    Mesh current collectors made of stainless steel (SS) can be integrated into microbial fuel cell (MFC) cathodes constructed of a reactive carbon black and Pt catalyst mixture and a poly(dimethylsiloxane) (PDMS) diffusion layer. It is shown here that the mesh properties of these cathodes can significantly affect performance. Cathodes made from the coarsest mesh (30-mesh) achieved the highest maximum power of 1616 ± 25 mW m-2 (normalized to cathode projected surface area; 47.1 ± 0.7 W m-3 based on liquid volume), while the finest mesh (120-mesh) had the lowest power density (599 ± 57 mW m-2). Electrochemical impedance spectroscopy showed that charge transfer and diffusion resistances decreased with increasing mesh opening size. In MFC tests, the cathode performance was primarily limited by reaction kinetics, and not mass transfer. Oxygen permeability increased with mesh opening size, accounting for the decreased diffusion resistance. At higher current densities, diffusion became a limiting factor, especially for fine mesh with low oxygen transfer coefficients. These results demonstrate the critical nature of the mesh size used for constructing MFC cathodes. © 2010 Elsevier B.V. All rights reserved.

  8. Numerical Simulation of Current Distribution in Cathode Carbon Block of an Aluminum Reduction Cell

    Science.gov (United States)

    Tao, Wenju; Li, Tuofu; Wang, Zhaowen; Gao, Bingliang; Shi, Zhongning; Hu, Xianwei; Cui, Jianzhong

    2015-11-01

    Cathode carbon block wear is the main limiting factor for the lifetime of aluminum reduction cells. The wear rate is enhanced by current density. In this article, the current distribution at the surface of carbon block was calculated using a thermoelectric coupled model. Then the effects of effective length ( l e), height of the cathode carbon block ( h c), and width and height of the collector ( w b and h b) on current distribution were investigated. The results show that l e has a great effect on the current distribution. With l e decreasing, the maximum current density increases rapidly and shifts toward the cell center. When the l e decreases from 1.67 m to 1.51 m, the maximum current density increases by 57.9%. Moreover, the maximum current density will be reduced with increasing h c or h b × w b. For h b × w b = 180 mm × 180 mm2, the maximum current density is reduced by 27.8%. However, increasing h c or h b × w b will decrease the temperature in the cathode carbon block. The results of this study may provide the database optimization of cell operation and design.

  9. Cathode erosion in high-current high-pressure arc

    CERN Document Server

    Nemchinsky, V A

    2003-01-01

    Cathode erosion rate was experimentally investigated for two types of arcs: one with tungsten cathode in nitrogen atmosphere and one with hafnium cathode in oxygen atmosphere. Conditions were typical for plasma arc cutting systems: gas pressure from 2 to 5 atm, arc current from 200 to 400 A, gas flow rate from 50 to 130 litre min sup - sup 1. It was found that the actual cathode evaporation rate G is much lower than G sub 0 , the evaporation rate that follows from the Hertz-Knudsen formula: G = nu G sub 0. The difference is because some of the evaporated particles return back to the cathode. For conditions of our experiments, the factor nu could be as low as 0.01. It was shown experimentally that nu depends strongly on the gas flow pattern close to the cathode. In particular, swirling the gas increases nu many times. To explain the influence of gas swirling, model calculations of gas flows were performed. These calculations revealed difference between swirling and non-swirling flows: swirling the gas enhances...

  10. Asymmetric battery having a semi-solid cathode and high energy density anode

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Taison; Chiang, Yet-Ming; Ota, Naoki; Wilder, Throop; Duduta, Mihai

    2016-09-06

    Embodiments described herein relate generally to devices, systems and methods of producing high energy density batteries having a semi-solid cathode that is thicker than the anode. An electrochemical cell can include a positive electrode current collector, a negative electrode current collector and an ion-permeable membrane disposed between the positive electrode current collector and the negative electrode current collector. The ion-permeable membrane is spaced a first distance from the positive electrode current collector and at least partially defines a positive electroactive zone. The ion-permeable membrane is spaced a second distance from the negative electrode current collector and at least partially defines a negative electroactive zone. The second distance is less than the first distance. A semi-solid cathode that includes a suspension of an active material and a conductive material in a non-aqueous liquid electrolyte is disposed in the positive electroactive zone, and an anode is disposed in the negative electroactive zone.

  11. Design and characterization of the annular cathode high current pulsed electron beam source for circular components

    Science.gov (United States)

    Jiang, Wei; Wang, Langping; Wang, Xiaofeng

    2016-08-01

    In order to irradiate circular components with high current pulsed electron beam (HCPEB), an annular cathode based on carbon fiber bunches was designed and fabricated. Using an acceleration voltage of 25 kV, the maximum pulsed irradiation current and energy of this annular cathode can reach 7.9 kA and 300 J, respectively. The irradiation current density distribution of the annular cathode HCPEB source measured along the circumferential direction shows that the annular cathode has good emission uniformity. In addition, four 9310 steel substrates fixed uniformly along the circumferential direction of a metal ring substrate were irradiated by this annular cathode HCPEB source. The surface and cross-section morphologies of the irradiated samples were characterized by scanning electron microscopy (SEM). SEM images of the surface reveal that crater and surface undulation have been formed, which hints that the irradiation energy of the HCPEB process is large enough for surface modification of 9310 steel. Meanwhile, SEM cross-section images exhibit that remelted layers with a thickness of about 5.4 μm have been obtained in all samples, which proves that a good practical irradiation uniformity can be achieved by this annular cathode HCPEB source.

  12. Plasma-induced evolution behavior of space-charge-limited current for multiple-needle cathodes

    International Nuclear Information System (INIS)

    Properties of the plasma and beam flow produced by tufted carbon fiber cathodes in a diode powered by a ∼500 kV, ∼400 ns pulse are investigated. Under electric fields of 230-260 kV cm-1, the electron current density was in the range 210-280 A cm-2, and particularly at the diode gap of 20 mm, a maximum beam power density of about 120 MW cm-2 was obtained. It was found that space-charge-limited current exhibited an evolution behavior as the accelerating pulse proceeded. There exists a direct relation between the movement of plasma within the diode and the evolution of space-charge-limited current. Initially in the accelerating pulse, the application of strong electric fields caused the emission sites to explode, forming cathode flares or plasma spots, and in this stage the space-charge-limited current was approximately described by a multiple-needle cathode model. As the pulse proceeded, these plasma spots merged and expanded towards the anode, thus increasing the emission area and shortening the diode gap, and the corresponding space-charge-limited current followed a planar cathode model. Finally, the space-charge-limited current is developed from a unipolar flow into a bipolar flow as a result of the appearance of anode plasma. In spite of the nonuniform distribution of cathode plasma, the cross-sectional uniformity of the extracted electron beam is satisfactory. The plasma expansion within the diode is found to be a major factor in the diode perveance growth and instability. These results show that these types of cathodes can offer promising applications for high-power microwave tubes.

  13. HIGH-CURRENT COLD CATHODE FIELD EMISSION ARRAY FOR ELECTRON LENS APPLICATION

    Energy Technology Data Exchange (ETDEWEB)

    Hirshfield, Jay L

    2012-12-28

    During Phase I, the following goals were achieved: (1) design and fabrication of a novel, nano-dimensional CNT field emitter assembly for high current density application, with high durability; (2) fabrication of a ceramic based micro channel plate (MCP) and characterization of its secondary electron emission; and (3) characterizing the CNT/MCP cathode for high field emission and durability. As a result of these achievements, a relatively high current density of ~ 1.2 A/cm2 from a CNT cathode and single channel MCP were measured. The emission current was also extremely stable with a peak-to-peak variation of only 1.8%. The emission current could be further enhanced to meet requirements for electron lens applications by increasing the number of MCP channels. A calculation for maximum possible current density with a 1200 channel/cm2 MCP, placed over a cathode with 1200 uniformly functioning CNTs, would be ~1.46 kA/cm2, neglecting space charge limitations. Clearly this level of emission is far greater than what is needed for the electron lens application, but it does offer a highly comforting margin to account for sub-standard emitters and/or to allow the lesser challenge of building a cathode with fewer channels/cm2. A satisfactory goal for the electron lens application would be a controllable emission of 2-4 mA per channel in an ensemble of 800-1200 uniformly-functioning channels/cm2, and a cathode with overall area of about 1 cm2.

  14. Low-voltage operating mode of a high-current magnetized cold-cathode plasma

    Science.gov (United States)

    Sommerer, Timothy; Aceto, Steven; Smith, David; Hitchon, Nicholas; Lawler, James

    2015-09-01

    A series of approximations and simple models is used to estimate the properties of a cold-cathode plasma in a high-voltage, high-power gas switch for use in grid-scale electric power conversion. The active plasma volume is a plane-parallel gap ~1 cm filled with helium at a pressure on order 0.1 torr. A magnetic field in the region adjacent to the cathode is used to increase the current density to practical levels >1 A/cm2. The plasma can operate in a ``low voltage mode'' (~80 V) that has the appearance of a constricted attachment at the cathode surface and a more diffuse region toward the anode. Cathode material is absent from the plasma emission spectrum. Various attempts to model the spot indicate that the plasma in the constriction is near full ionization, and that there is a dynamic balance of neutral gas atoms between the constriction, the cathode surface, and the neighboring diffuse plasma. The electron emission mechanism is assumed to be conventional, by ion impact, but field emission may contribute. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000298.

  15. Ultrasound Current Source Density Imaging

    OpenAIRE

    Olafsson, Ragnar; Witte, Russell S.; Huang, Sheng-Wen; O’Donnell, Matthew

    2008-01-01

    Surgery to correct severe heart arrhythmias usually requires detailed maps of the cardiac activation wave prior to ablation. The pinpoint electrical mapping procedure is laborious and limited by its spatial resolution (5–10 mm). We propose ultrasound current source density imaging (UCSDI), a direct 3-D imaging technique that potentially facilitates existing mapping procedures with superior spatial resolution. The technique is based on a pressure-induced change in resistivity known as the acou...

  16. Experimental research of different plasma cathodes for generation of high-current electron beams

    International Nuclear Information System (INIS)

    The results of experimental studies of different types of cathodes—carbon-epoxy rods, carbon-epoxy capillary, edged graphite, and metal-dielectric—under the application of high-voltage pulses with an amplitude of several hundreds of kV and pulse duration of several nanoseconds are presented. The best diode performance was achieved with the edged graphite and carbon-epoxy-based cathodes characterized by uniform and fast (<1 ns) formation of explosive emission plasma spots and quasi-constant diode impedance. This result was achieved for both annular cathodes in a strong magnetic field and planar cathodes of a similar diameter (∼2 cm) with no external magnetic field. The cathodes based on carbon-epoxy rods and carbon-epoxy capillaries operating with an average current density up to 1 kA/cm2 showed insignificant erosion along 106 pulses of the generator and the generated electron beam current showed excellent reproducibility in terms of the amplitude and waveform

  17. Experimental research of different plasma cathodes for generation of high-current electron beams

    Energy Technology Data Exchange (ETDEWEB)

    Shafir, G.; Kreif, M.; Gleizer, J. Z.; Gleizer, S.; Krasik, Ya. E. [Physics Department, Technion, Haifa 32000 (Israel); Gunin, A. V.; Kutenkov, O. P.; Rostov, V. V. [Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk 634055 (Russian Federation); Pegel, I. V. [Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk 634055 (Russian Federation); Tomsk Polytechnic University, Tomsk 634034 (Russian Federation)

    2015-11-21

    The results of experimental studies of different types of cathodes—carbon-epoxy rods, carbon-epoxy capillary, edged graphite, and metal-dielectric—under the application of high-voltage pulses with an amplitude of several hundreds of kV and pulse duration of several nanoseconds are presented. The best diode performance was achieved with the edged graphite and carbon-epoxy-based cathodes characterized by uniform and fast (<1 ns) formation of explosive emission plasma spots and quasi-constant diode impedance. This result was achieved for both annular cathodes in a strong magnetic field and planar cathodes of a similar diameter (∼2 cm) with no external magnetic field. The cathodes based on carbon-epoxy rods and carbon-epoxy capillaries operating with an average current density up to 1 kA/cm{sup 2} showed insignificant erosion along 10{sup 6} pulses of the generator and the generated electron beam current showed excellent reproducibility in terms of the amplitude and waveform.

  18. New approaches for high energy density lithium-sulfur battery cathodes.

    Science.gov (United States)

    Evers, Scott; Nazar, Linda F

    2013-05-21

    The goal of replacing combustion engines or reducing their use presents a daunting problem for society. Current lithium-ion technologies provide a stepping stone for this dramatic but inevitable change. However, the theoretical gravimetric capacity (∼300 mA h g(-1)) is too low to overcome the problems of limited range in electric vehicles, and their cost is too high to sustain the commercial viability of electrified transportation. Sulfur is the one of the most promising next generation cathode materials. Since the 1960s, researchers have studied sulfur as a cathode, but only recently have great strides been made in preparing viable composites that can be used commercially. Sulfur batteries implement inexpensive, earth-abundant elements at the cathode while offering up to a five-fold increase in energy density compared with present Li-ion batteries. Over the past few years, researchers have come closer to solving the challenges associated with the sulfur cathode. Using carbon or conducting polymers, researchers have wired up sulfur, an excellent insulator, successfully. These conductive hosts also function to encapsulate the active sulfur mass upon reduction/oxidation when highly soluble lithium polysulfides are formed. These soluble discharge products remain a crux of the Li-S cell and need to be contained in order to increase cycle life and capacity retention. The use of mesoporous carbons and tailored designs featuring porous carbon hollow spheres have led to highly stable discharge capacities greater than 900 mA h g(-1) over 100 cycles. In an attempt to fully limit polysulfide dissolution, methods that rely on coating carbon/sulfur composites with polymers have led to surprisingly stable capacities (∼90% of initial capacity retained). Additives will also play an important role in sulfur electrode design. For example, small fractions (> 3 wt%) of porous silica or titania effectively act as polysulfide reservoirs, decreasing their concentration in the

  19. Advanced Cathode Material For High Energy Density Lithium-Batteries Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Advanced cathode materials having high red-ox potential and high specific capacity offer great promise to the development of high energy density lithium-based...

  20. Measuring current emission and work functions of large thermionic cathodes

    International Nuclear Information System (INIS)

    As one component of the nations Stockpile Stewardship program, Los Alamos National Laboratory is constructing a 20 MeV, 2 kA (with a 4 kA upgrade capability), 3ps induction linac for doing x-ray radiography of explosive devices. The linac is one leg of a facility called the Dual-Axis Radiography Hydrodynamic Test Facility (DARHT). The electron gun is designed to operate at 3.2 MV. The gun is a Pierce type design and uses a 6.5' cathode for 2 kA operation and an 8' cathode for 4 kA operation. We have constructed a small facility called the Cathode Test Stand (CTS) to investigate engineering and physics issues regarding large thermionic dispenser-cathodes. In particular, we have looked at the issues of temperature uniformity on the cathode surface and cathode quality as measured by its work function. We have done thermal imaging of both 8' and 6.5' cathodes. Here we report on measurements of the cathode work function, both the average value and how it vanes across the face of the cathode.

  1. Current Density Measurements of an Annular-Geometry Ion Engine

    Science.gov (United States)

    Shastry, Rohit; Patterson, Michael J.; Herman, Daniel A.; Foster, John E.

    2012-01-01

    The concept of the annular-geometry ion engine, or AGI-Engine, has been shown to have many potential benefits when scaling electric propulsion technologies to higher power. However, the necessary asymmetric location of the discharge cathode away from thruster centerline could potentially lead to non-uniformities in the discharge not present in conventional geometry ion thrusters. In an effort to characterize the degree of this potential non-uniformity, a number of current density measurements were taken on a breadboard AGI-Engine. Fourteen button probes were used to measure the ion current density of the discharge along a perforated electrode that replaced the ion optics during conditions of simulated beam extraction. Three Faraday probes spaced apart in the vertical direction were also used in a separate test to interrogate the plume of the AGI-Engine during true beam extraction. It was determined that both the discharge and the plume of the AGI-Engine are highly uniform, with variations under most conditions limited to +/-10% of the average current density in the discharge and +/-5% of the average current density in the plume. Beam flatness parameter measured 30 mm from the ion optics ranged from 0.85 - 0.95, and overall uniformity was shown to generally increase with increasing discharge and beam currents. These measurements indicate that the plasma is highly uniform despite the asymmetric location of the discharge cathode.

  2. Elucidation of constant current density molecular plating

    International Nuclear Information System (INIS)

    The production of thin layers by means of constant current or constant voltage electrolysis in organic media is commonly known as molecular plating. Despite the fact that this method has been applied for decades and is known to be among the most efficient ones for obtaining quantitative deposition, a full elucidation of the molecular plating is still lacking. In order to get a general understanding of the process and hence set the basis for further improvements of the method, constant current density electrolysis experiments were carried out in a mixture of isopropanol and isobutanol containing millimolar amounts of HNO3 together with [Nd(NO3)3·6H2O] used as a model electrolyte. The process was investigated by considering the influence of different parameters, namely the electrolyte concentrations (i.e., Nd(NO3)3·6H2O: 0.11, 0.22, 0.44 mM, and HNO3: 0.3, 0.4 mM), the applied current (i.e., 2 mA and 6 mA), and the surface roughness of the deposition substrates (i.e., a few tens to several hundreds of nm). The response of the process to changes of these parameters was monitored recording cell potential curves, which showed to be strongly influenced by the investigated conditions. The produced layers were characterized using γ-ray spectroscopy for the evaluation of Nd deposition yields, X-ray photoelectron spectroscopy for chemical analysis of the surfaces, and atomic force microscopy for surface roughness evaluation. X-ray photoelectron spectroscopy results clearly indicate that Nd is present only as Nd3+ on the cathodic surface after molecular plating. The results obtained from this characterization and some basic features inferred from the study of the cell potential curves were used to interpret the different behaviours of the deposition processes as a consequence of the applied variables.

  3. Microbial Fuel Cell Cathodes With Poly(dimethylsiloxane) Diffusion Layers Constructed around Stainless Steel Mesh Current Collectors

    KAUST Repository

    Zhang, Fang

    2010-02-15

    A new and simplified approach for making cathodes for microbial fuel cells (MFCs) was developed by using metal meshcurrent collectorsandinexpensive polymer/carbon diffusion layers (DLs). Rather than adding a current collector to a cathode material such as carbon cloth, we constructed the cathode around the metal mesh itself, thereby avoiding the need for the carbon cloth or other supporting material. A base layer of poly(dimethylsiloxane) (PDMS) and carbon black was applied to the air-side of a stainless steel mesh, and Pt on carbon black with Nafion binder was applied to the solutionside as catalyst for oxygen reduction. The PDMS prevented water leakage and functioned as a DL by limiting oxygen transfer through the cathode and improving coulombic efficiency. PDMS is hydrophobic, stable, and less expensive than other DL materials, such as PTFE, that are commonly applied to air cathodes. Multiple PDMS/carbon layers were applied in order to optimize the performance of the cathode. Two PDMS/ carbon layers achieved the highest maximum power density of 1610 ± 56 mW/m 2 (normalized to cathode projected surface area; 47.0 ± 1.6 W/m3 based on liquid volume). This power output was comparable to the best result of 1635 ± 62 mW/m2 obtained using carbon cloth with three PDMS/carbon layers and a Pt catalyst. The coulombic efficiency of the mesh cathodes reached more than 80%, and was much higher than the maximum of 57% obtained with carbon cloth. These findings demonstrate that cathodes can be constructed around metal mesh materials such as stainless steel, and that an inexpensive coating of PDMS can prevent water leakage and lead to improved coulombic efficiencies. © 2010 American Chemical Society.

  4. Existence of a virtual cathode close to a strongly electron emissive wall in low density plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Tierno, S. P., E-mail: sp.tierno@upm.es; Donoso, J. M.; Domenech-Garret, J. L.; Conde, L. [Department of Applied Physics, E.T.S.I. Aeronáutica y del Espacio. Universidad Politécnica de Madrid, 28040 Madrid (Spain)

    2016-01-15

    The interaction between an electron emissive wall, electrically biased in a plasma, is revisited through a simple fluid model. We search for realistic conditions of the existence of a non-monotonic plasma potential profile with a virtual cathode as it is observed in several experiments. We mainly focus our attention on thermionic emission related to the operation of emissive probes for plasma diagnostics, although most conclusions also apply to other electron emission processes. An extended Bohm criterion is derived involving the ratio between the two different electron densities at the potential minimum and at the background plasma. The model allows a phase-diagram analysis, which confirms the existence of the non-monotonic potential profiles with a virtual cathode. This analysis shows that the formation of the potential well critically depends on the emitted electron current and on the velocity at the sheath edge of cold ions flowing from the bulk plasma. As a consequence, a threshold value of the governing parameter is required, in accordance to the physical nature of the electron emission process. The latter is a threshold wall temperature in the case of thermionic electrons. Experimental evidence supports our numerical calculations of this threshold temperature. Besides this, the potential well becomes deeper with increasing electron emission, retaining a fraction of the released current which limits the extent of the bulk plasma perturbation. This noninvasive property would explain the reliable measurements of plasma potential by using the floating potential method of emissive probes operating in the so-called strong emission regime.

  5. Simulating different modes of current transfer to thermionic cathodes in a wide range of conditions

    Energy Technology Data Exchange (ETDEWEB)

    Benilov, M S; Cunha, M D; Faria, M J [Departamento de Fisica, Universidade da Madeira, Largo do MunicIpio, 9000 Funchal (Portugal)

    2009-07-21

    Changes in the pattern of steady-state modes of current transfer to thermionic cathodes induced by variations of the cathode geometry and temperature of the cooling fluid are studied numerically. For some combinations of control parameters, only one stable mode in a wide current range exists, which combines features of spot and diffuse modes. This mode, when attached to an elongated protrusion on the cathode surface, may be identified with the so-called super spot mode observed in experiments on low-current arcs. There is also reasonable agreement between the modelling and the experiment on cathodes of high-current arcs operating in the diffuse mode. The conclusions on existence under certain conditions of only one stable mode in a wide current range and of a minimum of the dependence of the temperature of the hottest point of the cathode on the arc current, manifested by this mode, may have industrial importance and admit a straightforward experimental verification.

  6. Degradation behavior of anode-supported solid oxide fuel cell using LNF cathode as function of current load

    Energy Technology Data Exchange (ETDEWEB)

    Komatsu, Takeshi; Yoshida, Yoshiteru; Watanabe, Kimitaka; Chiba, Reiichi; Taguchi, Hiroaki; Orui, Himeko; Arai, Hajime [NTT Energy and Environment Systems Laboratories, Atsugi-shi, Kanagawa 243-0198 (Japan)

    2010-09-01

    We investigated the effect of current loading on the degradation behavior of an anode-supported solid oxide fuel cell (SOFC). The cell consisted of LaNi{sub 0.6}Fe{sub 0.4}O{sub 3} (LNF), alumina-doped scandia stabilized zirconia (SASZ), and a Ni-SASZ cermet as the cathode, electrolyte, and anode, respectively. The test was carried out at 1073 K with constant loads of 0.3, 1.0, 1.5, and 2.3 A cm{sup -2}. The degradation rate, defined by the voltage loss during a fixed period (about 1000 h), was faster at higher current densities. From an impedance analysis, the degradation depended mainly on increases in the cathodic resistance, while the anodic and ohmic resistances contributed very little. The cathode microstructures were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). (author)

  7. Development of a high average current polarized electron source with long cathode operational lifetime

    Energy Technology Data Exchange (ETDEWEB)

    C. K. Sinclair; P. A. Adderley; B. M. Dunham; J. C. Hansknecht; P. Hartmann; M. Poelker; J. S. Price; P. M. Rutt; W. J. Schneider; M. Steigerwald

    2007-02-01

    Substantially more than half of the electromagnetic nuclear physics experiments conducted at the Continuous Electron Beam Accelerator Facility of the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory) require highly polarized electron beams, often at high average current. Spin-polarized electrons are produced by photoemission from various GaAs-based semiconductor photocathodes, using circularly polarized laser light with photon energy slightly larger than the semiconductor band gap. The photocathodes are prepared by activation of the clean semiconductor surface to negative electron affinity using cesium and oxidation. Historically, in many laboratories worldwide, these photocathodes have had short operational lifetimes at high average current, and have often deteriorated fairly quickly in ultrahigh vacuum even without electron beam delivery. At Jefferson Lab, we have developed a polarized electron source in which the photocathodes degrade exceptionally slowly without electron emission, and in which ion back bombardment is the predominant mechanism limiting the operational lifetime of the cathodes during electron emission. We have reproducibly obtained cathode 1/e dark lifetimes over two years, and 1/e charge density and charge lifetimes during electron beam delivery of over 2?105???C/cm2 and 200 C, respectively. This source is able to support uninterrupted high average current polarized beam delivery to three experimental halls simultaneously for many months at a time. Many of the techniques we report here are directly applicable to the development of GaAs photoemission electron guns to deliver high average current, high brightness unpolarized beams.

  8. High-Current Cold Cathode Employing Diamond and Related Materials

    Energy Technology Data Exchange (ETDEWEB)

    Hirshfield, Jay L. [Omega-P, Inc., New Haven, CT (United States)

    2014-10-22

    The essence of this project was for diamond films to be deposited on cold cathodes to improve their emission properties. Films with varying morphology, composition, and size of the crystals were deposited and the emission properties of the cathodes that utilize such films were studied. The prototype cathodes fabricated by the methods developed during Phase I were tested and evaluated in an actual high-power RF device during Phase II. These high-power tests used the novel active RF pulse compression system and the X-band magnicon test facility at US Naval Research Laboratory. In earlier tests, plasma switches were employed, while tests under this project utilized electron-beam switching. The intense electron beams required in the switches were supplied from cold cathodes embodying diamond films with varying morphology, including uncoated molybdenum cathodes in the preliminary tests. Tests with uncoated molybdenum cathodes produced compressed X-band RF pulses with a peak power of 91 MW, and a maximum power gain of 16.5:1. Tests were also carried out with switches employing diamond coated cathodes. The pulse compressor was based on use of switches employing electron beam triggering to effect mode conversion. In experimental tests, the compressor produced 165 MW in a ~ 20 ns pulse at ~18× power gain and ~ 140 MW at ~ 16× power gain in a 16 ns pulse with a ~ 7 ns flat-top. In these tests, molybdenum blade cathodes with thin diamond coatings demonstrated good reproducible emission uniformity with a 100 kV, 100 ns high voltage pulse. The new compressor does not have the limitations of earlier types of active pulse compressors and can operate at significantly higher electric fields without breakdown.

  9. Cathodic current enhancement via manganese and oxygen related reactions in marine biofilms

    Science.gov (United States)

    Strom, Matthew James

    Corrosion is a threat that has economic, and environmental impacts worldwide. Many types of corrosive attack are the subject of ongoing research. One of these areas of research is microbiologically influenced corrosion, which is the enhancement and/or initiation of corrosion events caused by microorganisms. It is well known that colonies of microorganisms can enhance cathodic currents through biofilm formation. The aim of the present work was to elucidate the role of manganese in enhancing cathodic currents in the presence of biofilms. Repeated polarizations conducted in Delaware Bay waters, on biofilm coated Cr identified potentially sustainable reduction reactions. The reduction of MnO2 and the enhancement of the oxygen reduction reaction (ORR) were proven to be factors that influence cathodic current enhancement. The removal of ambient oxygen during polarizations resulted in a shutdown of cathodic current enhancement. These field data led to an exploration of the synergistic relationship between MnO2 and the ORR. Laboratory studies of the catalysis of peroxide disproportionation by MnO2 were monitored using a hanging mercury drop electrode. Experiments were run at an ambient sweater pH of 8 and pH 9, which simulated the near-surface conditions typical of cathodes immersed in seawater. Rapid reoxidation at the more basic pH was shown to allow manganese to behave as a persistent catalyst under the typical electrochemical surface conditions of a cathode. As a result a mechanism for ORR enhancement by manganese was proposed as a unique mechanism for cathodic current enhancement in biofilms. A separate field study of Delaware biofilms on stainless steel coupled to a sacrificial Al anode was carried out to identify the ORR enhancement mechanism and sustainable redox reactions at the cathode. Chemical treatments of glutaraldehyde and formaldoxime were applied to cathodes with biofilms to distinguish between enzymatic and MnO2 related ORR enhancement. The results ruled

  10. Current density imaging during tissue electroporation

    International Nuclear Information System (INIS)

    Delivery of externally applied electric pulses on the target tissue during electroporation increases membrane permeability and induces electric currents in the tissue. To optimize electroporation parameters, the current density and with it associated electric field distributions can be monitored by means of current density imaging (CDI) and magnetic resonance electric impedance tomography (MREIT). (Author)

  11. Electrochemical reaction of sulfur cathodes with Ni foam current collector in Li-S batteries

    Science.gov (United States)

    Liu, Li-Jun; Chen, Yang; Zhang, Zhi-Feng; You, Xiao-Long; Walle, Maru Dessie; Li, Ya-Juan; Liu, You-Nian

    2016-09-01

    The electrochemical properties of sulfur cathode with Ni foam current collector are investigated in detail. Different from sulfur cathode with stain steel current collector, it is interesting found that novel redox peaks at 1.95 V/1.35 V are observed for sulfur cathode with Ni foam. The electrochemical behavior is further verified by ex-situ XRD, SEM and XPS analyses. The results indicate that Ni foam current collector is involved in the redox reaction in Li/S rechargeable battery, and NiS forms at the surface of the Ni foam. These results demonstrate that the sulfur electrode is transformed into NiS.

  12. DENSITY CURRENTS IN ACTIVATED SLUDGE SECONDARY CLARIFIERS

    Science.gov (United States)

    Density currents form in activated sludge secondary clarifiers because the mixed liquor has a density greater than the treated wastewater in the clarifier. This causes the mixed liquor to plunge to the bottom of the clarifier establishing relatively high velocity currents within ...

  13. Current density and state density in diluted magnetic semiconductor nanostructures

    Science.gov (United States)

    Pérez Merchancano, S. T.; Paredes Gutiérrez, H.; Zuñiga, J. A.

    2016-02-01

    We study in this paper the spin-polarized current density components in diluted magnetic semiconductor tunnelling diodes with different sample geometries. We calculate the resonant JxV and the density of states. The differential conductance curves are analyzed as functions of the applied voltage and the magnetic potential strength induced by the magnetic ions.

  14. Phenomenology of plasma engine cathodes at high current rates and low pressures

    Science.gov (United States)

    Huegel, H.; Kruelle, G.

    1984-01-01

    The effects of low surrounding pressures on cathodes of arc jet engines with electromagnetic acceleration are investigated for pressure and current energies of 20 to 100 Torr. and 400 to 1000 A. Experiments with 50 mm long and 8 mm diameter tungsten-thorium cathode in a coaxial gas flow show that pre-heating of the cathode reduces the duration of the instable arc discharge and thus material loss. The use of lighter gases also reduces instability effects, as well as the use of increased pressures and a massive gas influx.

  15. Critical parameters governing energy density of Li-storage cathode materials unraveled by confirmatory factor analysis

    Science.gov (United States)

    Sohn, Kee-Sun; Han, Su Cheol; Park, Woon Bae; Pyo, Myoungho

    2016-03-01

    Despite extensive effort during the past few decades, a comprehensive understanding of the key variables governing the electrochemical properties of cathode materials in Li-ion batteries is still far from complete. To elucidate the critical parameters affecting energy density (ED) and capacity (Q) retention in layer and spinel cathodes, we data-mine the existing experimental data via confirmatory factor analysis (CFA) based on a structural equation model (SEM), which is a proven, versatile tool in understanding complex problems in the social science. The data sets are composed of 18 and 15 parameters extracted from 38 layer and 33 spinel compounds, respectively. CFA reveals the irrelevance of Q retention to all the parameters we adopt, but it also reveals the sensitive variations of ED with specific parameters. We validate the usefulness of CFA in material science and pinpointed critical parameters for high-ED cathodes, hoping to suggest a new insight in materials design.

  16. Influence of emission threshold of explosive emission cathodes on current waveform in foilless diodes

    International Nuclear Information System (INIS)

    The emission threshold of explosive emission cathodes (EECs) is an important factor for beam quality. It can affect the explosive emission delay time, the plasma expansion process on the cathode surface, and even the current amplitude when the current is not fully space-charge-limited. This paper researches the influence of the emission threshold of an annular EEC on the current waveform in a foilless diode when the current is measured by a Rogowski coil. The particle-in-cell simulation which is performed under some tolerable and necessary simplifications shows that the long explosive emission delay time of high-threshold cathodes may leave an apparent peak of displacement current on the rise edge of the current waveform, and this will occur only when the electron emission starts after this peak. The experimental researches, which are performed under a diode voltage of 1 MV and a repetitive frequency of 20 Hz, demonstrate that the graphite cathode has a lower emission threshold and a longer lifetime than the stainless steel cathode according to the variation of the peak of displacement current on the rise edge of the current waveform

  17. Self-pulsing in a low-current hollow cathode discharge: From Townsend to glow discharge

    International Nuclear Information System (INIS)

    We investigate the self-pulsing phenomenon of a low current cavity discharge in a cylindrical hollow cathode in pure argon. The waveforms of pulsed current and voltage are measured, and the time-averaged and time-resolved images of hollow cathode discharge are recorded by using high-speed intensified charge coupled device camera. The results show that the self-pulsing is a mode transition between low-current stage of Townsend discharge and high-current stage of glow discharge. During the self-pulsing, the current rising time relates to the dissipation of space charges, and the decay time relates to the reconstruction of the virtual anode by the accumulation of positive ions. Whether or not space charges can form and keep the virtual anode is responsible for the discharge mode and hence plays an important role in the self-pulsing phenomenon in low current hollow cathode discharge

  18. Self-pulsing in a low-current hollow cathode discharge: From Townsend to glow discharge

    Energy Technology Data Exchange (ETDEWEB)

    Qin, Yu [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081 (China); Xie, Kan, E-mail: xiekan@bit.edu.cn [School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081 (China); Zhang, Yu; Ouyang, Jiting [School of Physics, Beijing Institute of Technology, Beijing 100081 (China)

    2016-02-15

    We investigate the self-pulsing phenomenon of a low current cavity discharge in a cylindrical hollow cathode in pure argon. The waveforms of pulsed current and voltage are measured, and the time-averaged and time-resolved images of hollow cathode discharge are recorded by using high-speed intensified charge coupled device camera. The results show that the self-pulsing is a mode transition between low-current stage of Townsend discharge and high-current stage of glow discharge. During the self-pulsing, the current rising time relates to the dissipation of space charges, and the decay time relates to the reconstruction of the virtual anode by the accumulation of positive ions. Whether or not space charges can form and keep the virtual anode is responsible for the discharge mode and hence plays an important role in the self-pulsing phenomenon in low current hollow cathode discharge.

  19. Critical current densities in superconducting materials

    Indian Academy of Sciences (India)

    P Chaddah

    2003-02-01

    We discuss recent research in the area of critical current densities $(J_C)$ in superconductors. This shall cover recent work on newly discovered superconductors, as well as on the magnetic-field dependence of $J_C$.

  20. The Fluid Mechanics of Pyroclastic Density Currents

    Science.gov (United States)

    Dufek, Josef

    2016-01-01

    Pyroclastic density currents are generated in explosive volcanic eruptions when gas and particle mixtures remain denser than the surrounding atmosphere. These mobile currents have a diversity of flow regimes, from energetic granular flows to turbulent suspensions. Given their hazardous nature, much of our understanding of the internal dynamics of these currents has been explored through mathematical and computational models. This review discusses the anatomy of these currents and their phenomenology and places these observations in the context of forces driving the currents. All aspects of the current dynamics are influenced by multiphase interactions, and the study of these currents offers insight into a high-energy end-member of multiphase flow. At low concentration, momentum transfer is dominated by particle-gas drag. At higher concentration, particle collisions, friction, and gas pore pressure act to redistribute momentum. This review examines end-member theoretical models for dilute and concentrated flow and then considers insight gained from multiphase simulations of pyroclastic density currents.

  1. INFLUENCE OF VACUUM ARC PLASMA EVAPORATOR CATHODE GEOMETRY OF ON VALUE OF ADMISSIBLE ARC DISCHARGE CURRENT

    Directory of Open Access Journals (Sweden)

    I. A. Ivanou

    2015-01-01

    Full Text Available An analysis of main design parameters that determine a level of droplet formation intensity at the generating stage of plasma flow has been given in the paper. The paper considers the most widely used designs of water cooled consumable cathodes. Ti or Ti–Si and Fe–Cr alloys have been taken as a material for cathodes. The following calculated data: average ionic charge Zi for titanium plasma +1.6; for «titanium–silicon plasma» +1.2, an electronic discharge 1.6022 ⋅ 10–19 C, an ion velocity vi = 2 ⋅ 104 m/s, an effective volt energy equivalent of heat flow diverted in the cathode Uк = 12 V, temperature of erosion cathode surface Тп = 550 К; temperature of the cooled cathode surface То = 350 К have been accepted in order to determine dependence of a maximum admissible arc discharge current on cathode height. The calculations have been carried out for various values of the cathode heights hк (from 0.02 to 0.05 m. Diameter of a target cathode is equal to 0.08 m for a majority of technological plasma devices, therefore, the area of the erosion surface is S = 0.005 m2.A thickness selection for a consumable target cathode part in the vacuum arc plasma source has been justified in the paper. The thickness ensures formation of minimum drop phase in the plasma flow during arc cathode material evaporation. It has been shown that a maximum admissible current of an arc discharge is practically equal to the minimum current of stable arcing when thickness of the consumable cathode part is equal to 0.05 m. The admissible discharge current can be rather significant and ensure high productivity during coating process with formation of relatively low amount of droplet phase in the coating at small values of hк.

  2. Optimal geometry toward uniform current density electrodes

    International Nuclear Information System (INIS)

    Electrodes are commonly used to inject current into the human body in various biomedical applications such as functional electrical stimulation, defibrillation, electrosurgery, RF ablation, impedance imaging, and so on. When a highly conducting electrode makes direct contact with biological tissues, the induced current density has strong singularity along the periphery of the electrode, which may cause painful sensation or burn. Especially in impedance imaging methods such as the magnetic resonance electrical impedance tomography, we should avoid such singularity since more uniform current density underneath a current-injection electrode is desirable. In this paper, we study an optimal geometry of a recessed electrode to produce a well-distributed current density on the contact area under the electrode. We investigate the geometry of the electrode surface to minimize the edge singularity and produce nearly uniform current density on the contact area. We propose a mathematical framework for the uniform current density electrode and its optimal geometry. The theoretical results are supported by numerical simulations

  3. Current-voltage characteristics of a cathodic plasma contactor with discharge chamber for application in electrodynamic tether propulsion

    Science.gov (United States)

    Xie, Kan; Martinez, Rafael A.; Williams, John D.

    2014-04-01

    This paper focuses on the net electron-emission current as a function of bias voltage of a plasma source that is being used as the cathodic element in a bare electrodynamic tether system. An analysis is made that enables an understanding of the basic issues determining the current-voltage (C-V) behaviour. This is important for the efficiency of the electrodynamic tether and for low impedance performance without relying on the properties of space plasma for varying orbital altitudes, inclinations, day-night cycles or the position of the plasma contactor relative to the wake of the spacecraft. The cathodic plasma contactor considered has a cylindrical discharge chamber (10 cm in diameter and ˜11 cm in length) and is driven by a hollow cathode. Experiments and a 1D spherical model are both used to study the contactor's C-V curves. The experiments demonstrate how the cathodic contactor would emit electrons into space for anode voltages in the range of 25-40 V, discharge currents in the range of 1-2.5 A, and low xenon gas flows of 2-4 sccm. Plasma properties are measured and compared with (3 A) and without net electron emission. A study of the dependence of relevant parameters found that the C-V behaviour strongly depends on electron temperature, initial ion energy and ion emission current at the contactor exit. However, it depended only weakly on ambient plasma density. The error in the developed model compared with the experimental C-V curves is within 5% at low electron-emission currents (0-2 A). The external ionization processes and high ion production rate caused by the discharge chamber, which dominate the C-V behaviour at electron-emission currents over 2 A, are further highlighted and discussed.

  4. External Mass Injection to Reduce Energetic Ion Production in the Discharge Plume of High Current Hollow Cathodes

    OpenAIRE

    Chu, Emily

    2012-01-01

    Hollow cathode discharge studies have shown the existence of energetic ions at high discharge currents that are likely responsible for the high erosion rates and erosion patterns observed on the keeper electrode of the hollow cathode. This thesis uses experimental methods to study the effects of neutral gas injection in the xenon hollow cathode discharge plume on the production of energetic ions to determine the injection conditions that yield optimum hollow cathode operation and life. Para...

  5. Current waveform reconstruction from an explosively emissive cathode at a subnanosecond voltage front

    Energy Technology Data Exchange (ETDEWEB)

    Sharypov, K. A., E-mail: const@iep.uran.ru; Ul' masculov, M. R.; Shpak, V. G.; Shunailov, S. A.; Yalandin, M. I. [Institute of Electrophysics UB RAS, 106 Amundsen Str., 620016 Ekaterinburg (Russian Federation); Mesyats, G. A. [P. N. Lebedev Physical Institute, RAS, 53, Lenin Avenue, 119991 Moscow (Russian Federation); Rostov, V. V. [Institute of High Current Electronics SB RAS, 2/3 Akademichesky Avenue, 634055 Tomsk (Russian Federation); Kolomiets, M. D. [Ural Federal University, 19, Mira Str., 620002 Ekaterinburg (Russian Federation)

    2014-12-15

    We describe the methods of registration and reconstruction of an envelope of explosive electron emission current from the edge of a cylindrical cathode, which provides a picosecond time reference of the emitted electron beam with a subnanosecond voltage front applied to the accelerating gap. Variation of the front steepness allows one to determine the beam onset time in the experiments, where a collector-type current probe can be used. The advanced method of dynamic time domain reflectometry provides exact data on electron beam current rise and track changes in the cathode emission from pulse to pulse with a precision of less than 10 ps.

  6. Burnout current density of bismuth nanowires

    Science.gov (United States)

    Cornelius, T. W.; Picht, O.; Müller, S.; Neumann, R.; Völklein, F.; Karim, S.; Duan, J. L.

    2008-05-01

    Single bismuth nanowires with diameters ranging from 100nmto1μm were electrochemically deposited in ion track-etched single-pore polycarbonate membranes. The maximum current density the wires are able to carry was investigated by ramping up the current until failure occurred. It increases by three to four orders of magnitude for nanowires embedded in the template compared to bulk bismuth and rises with diminishing diameter. Simulations show that the wires are heated up electrically to the melting temperature. Since the surface-to-volume ratio rises with diminishing diameter, thinner wires dissipate the heat more efficiently to the surrounding polymer matrix and, thus, can tolerate larger current densities.

  7. Development and Testing of High Current Hollow Cathodes for High Power Hall Thrusters

    Science.gov (United States)

    Kamhawi, Hani; Van Noord, Jonathan

    2012-01-01

    NASA's Office of the Chief Technologist In-Space Propulsion project is sponsoring the testing and development of high power Hall thrusters for implementation in NASA missions. As part of the project, NASA Glenn Research Center is developing and testing new high current hollow cathode assemblies that can meet and exceed the required discharge current and life-time requirements of high power Hall thrusters. This paper presents test results of three high current hollow cathode configurations. Test results indicated that two novel emitter configurations were able to attain lower peak emitter temperatures compared to state-of-the-art emitter configurations. One hollow cathode configuration attained a cathode orifice plate tip temperature of 1132 degC at a discharge current of 100 A. More specifically, test and analysis results indicated that a novel emitter configuration had minimal temperature gradient along its length. Future work will include cathode wear tests, and internal emitter temperature and plasma properties measurements along with detailed physics based modeling.

  8. Surface current density K: an introduction

    DEFF Research Database (Denmark)

    McAllister, Iain Wilson

    1991-01-01

    The author discusses the vector surface of current density K used in electrical insulation studies. K is related to the vector tangential electric field Kt at the surface of a body by the vector equation K=ΓE t where Γ represents the surface conductivity. The author derives a surface continuity...

  9. Study of Stable Cathodes and Electrolytes for High Specific Density Lithium-Air Battery

    Science.gov (United States)

    Hernandez-Lugo, Dionne M.; Wu, James; Bennett, William; Ming, Yu; Zhu, Yu

    2015-01-01

    Future NASA missions require high specific energy battery technologies, greater than 400 Wh/kg. Current NASA missions are using "state-of-the-art" (SOA) Li-ion batteries (LIB), which consist of a metal oxide cathode, a graphite anode and an organic electrolyte. NASA Glenn Research Center is currently studying the physical and electrochemical properties of the anode-electrolyte interface for ionic liquid based Li-air batteries. The voltage-time profiles for Pyr13FSI and Pyr14TFSI ionic liquids electrolytes studies on symmetric cells show low over-potentials and no dendritic lithium morphology. Cyclic voltammetry measurements indicate that these ionic liquids have a wide electrochemical window. As a continuation of this work, sp2 carbon cathode and these low flammability electrolytes were paired and the physical and electrochemical properties were studied in a Li-air battery system under an oxygen environment.

  10. A mathematical model of the current density distribution in electrochemical cells - AUTHORS’ REVIEW

    Directory of Open Access Journals (Sweden)

    PREDRAG M. ŽIVKOVIĆ

    2011-06-01

    Full Text Available An approach based on the equations of electrochemical kinetics for the estimation of the current density distribution in electrochemical cells is presented. This approach was employed for a theoretical explanation of the phenomena of the edge and corner effects. The effects of the geometry of the system, the kinetic parameters of the cathode reactions and the resistivity of the solution are also discussed. A procedure for a complete analysis of the current distribution in electrochemical cells is presented.

  11. Formation of current density profile in tilted current sheets

    Directory of Open Access Journals (Sweden)

    A. A. Petrukovich

    2008-11-01

    Full Text Available We investigate Cluster observations of strongly tilted sheets (flapping events in the magnetotail. In accordance with the simple model of slip deformation (vertical differential displacement of neighboring flux tubes, the Jy current density component in the tilted sheet remains constant and equal to that in the horizontal undisturbed sheet. However, a substantial Jz component appears proportional to the local sheet tilt. Slip-type variations, having smaller scale than the full crossing, locally change the tilt and Jz and may thus create a variety of non-classical (bifurcated, asymmetric etc current density profiles.

  12. Current density and continuity in discretized models

    International Nuclear Information System (INIS)

    Discrete approaches have long been used in numerical modelling of physical systems in both research and teaching. Discrete versions of the Schroedinger equation employing either one or several basis functions per mesh point are often used by senior undergraduates and beginning graduate students in computational physics projects. In studying discrete models, students can encounter conceptual difficulties with the representation of the current and its divergence because different finite-difference expressions, all of which reduce to the current density in the continuous limit, measure different physical quantities. Understanding these different discrete currents is essential and requires a careful analysis of the current operator, the divergence of the current and the continuity equation. Here we develop point forms of the current and its divergence valid for an arbitrary mesh and basis. We show that in discrete models currents exist only along lines joining atomic sites (or mesh points). Using these results, we derive a discrete analogue of the divergence theorem and demonstrate probability conservation in a purely localized-basis approach.

  13. Comparison of 2 Cathode Geometries for High Current (2 kA) Diodes

    CERN Document Server

    Pichoff, N

    2004-01-01

    AIRIX (FRANCE) and DARHT axis-1 (USA) are two high current accelerators designed for flash X-ray radiography. The electron beam produced (2 kA, 3.5 to 3.8 MV, 60 ns) is extracted from a velvet cold cathode. Specific calculations have demonstrated the influence of the cathode geometry on the emitted beam profile [1]. To check this assumption we have made two different experiments (DARHT March 2003 – AIRIX March 2004). We have compared the beam characteristics with two different geometries both theoretically and experimentally. The beam simulations have been done with 3 codes: a home-made code (M2V) and 2 commercial codes (PBGUNS and MAGIC). The extracted beam current and transverse profiles, for the first experiment, have been measured and compared to simulations results. In the second one, we have compared the beam’s extracted current and the energy spread.

  14. Steadiness in Dilute Pyroclastic Density Currents

    Science.gov (United States)

    Andrews, B. J.

    2015-12-01

    Pyroclastic density currents (PDCs) are often unsteady, as evidenced by direct observations of dilute lobes or jets emerging from the fronts of larger currents and by deposits that indicate transient transport and depositional regimes. We used scaled experiments to investigate unsteadiness in dilute PDCs. The experimental currents were run in an 8.5x6.1x2.6 m tank and comprised heated or ambient temperature 20-μm talc powder turbulently suspended in air. Experiments were scaled such that densimetric and thermal Richardson numbers, Froude number, and particle Stokes and settling numbers were dynamically similar to natural dilute PDCs. Although the experiment Reynolds numbers are substantially lower than those of natural PDCs, the experiments are fully turbulent. Experiments were observed with video and high-speed cameras and high-frequency thermocouples. Currents were generated with total eruption durations of 100 s. Unsteadiness in source conditions was produced by interrupting supply for intervals, t, with durations of 1, 2.5, 5, and 10 s in the experimental runs at 35 and 70 s. When t3t>τ, unsteadiness decays such that at a distance of ~4Ut, the currents are again steady. Applied to natural dilute PDCs, our results suggest that currents and their resulting deposits, will only show evidence of unsteadiness if they are disrupted for many seconds and those breaks may "heal" over distances of 100s of meters.

  15. Current Developments in Nuclear Density Functional Methods

    CERN Document Server

    Dobaczewski, J

    2010-01-01

    Density functional theory (DFT) became a universal approach to compute ground-state and excited configurations of many-electron systems held together by an external one-body potential in condensed-matter, atomic, and molecular physics. At present, the DFT strategy is also intensely studied and applied in the area of nuclear structure. The nuclear DFT, a natural extension of the self-consistent mean-field theory, is a tool of choice for computations of ground-state properties and low-lying excitations of medium-mass and heavy nuclei. Over the past thirty-odd years, a lot of experience was accumulated in implementing, adjusting, and using the density-functional methods in nuclei. This research direction is still extremely actively pursued. In particular, current developments concentrate on (i) attempts to improve the performance and precision delivered by the nuclear density-functional methods, (ii) derivations of density functionals from first principles rooted in the low-energy chromodynamics and effective th...

  16. Corrosion of ruthenium dioxide based cathodes in alkaline medium caused by reverse currents

    International Nuclear Information System (INIS)

    A reverse current obtained during power shutdowns in industrial processes, such as chlor-alkali production or alkaline water electrolysis, is deleterious for hydrogen evolving ruthenium dioxide (RuO2) based cathodes. It has been observed that RuO2 coatings after a power shutdown, necessary for e.g. maintenance, are severely damaged unless polarization rectifiers are employed. In this work we show why these types of cathodes are sensitive to reverse currents, i.e. anodic currents, after hydrogen evolution. RuO2 coatings deposited on nickel substrates were subjected to different electrochemical treatments such as hydrogen evolution, oxygen evolution, or reverse currents in 8 M NaOH at 90 °C. Polarity inversion was introduced after hydrogen evolution to simulate the effect of reverse currents. Because of chemical interaction with hydrogen, a significant amount of the RuO2 coating was transformed into hydroxylated species during cathodic polarization. Our study shows that these hydroxylated phases are highly sensitive to electrochemical corrosion during anodic polarization after extended hydrogen evolution

  17. Long Life Cold Cathodes for Hall effect Thrusters Project

    Data.gov (United States)

    National Aeronautics and Space Administration — An electron source incorporating long life, high current density cold cathodes inside a microchannel plate for use with ion thrusters is proposed. Cathode lifetime...

  18. Sulphur-impregnated flow cathode to enable high-energy-density lithium flow batteries

    Science.gov (United States)

    Chen, Hongning; Zou, Qingli; Liang, Zhuojian; Liu, Hao; Li, Quan; Lu, Yi-Chun

    2015-01-01

    Redox flow batteries are promising technologies for large-scale electricity storage, but have been suffering from low energy density and low volumetric capacity. Here we report a flow cathode that exploits highly concentrated sulphur-impregnated carbon composite, to achieve a catholyte volumetric capacity 294 Ah l-1 with long cycle life (>100 cycles), high columbic efficiency (>90%, 100 cycles) and high energy efficiency (>80%, 100 cycles). The demonstrated catholyte volumetric capacity is five times higher than the all-vanadium flow batteries (60 Ah l-1) and 3-6 times higher than the demonstrated lithium-polysulphide approaches (50-117 Ah l-1). Pseudo-in situ impedance and microscopy characterizations reveal superior electrochemical and morphological reversibility of the sulphur redox reactions. Our approach of exploiting sulphur-impregnated carbon composite in the flow cathode creates effective interfaces between the insulating sulphur and conductive carbon-percolating network and offers a promising direction to develop high-energy-density flow batteries.

  19. Current source density reconstruction from incomplete data

    OpenAIRE

    Wojcik, Daniel K.; Leski, Szymon

    2009-01-01

    We propose two ways of estimating the current source density (CSD) from measurements of voltage on a Cartesian grid with missing recording points using the inverse CSD method. The simplest approach is to substitute local averages (LA) in place of missing data. A more elaborate alternative is to estimate a smaller number of CSD parameters than the actual number of recordings and to take the least-squares fit (LS). We compare the two approaches in the three dimensional case on several sets of s...

  20. Pipeline integrity through cathodic protection

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, N. [Gas Authority India Ltd., New Delhi (India); Khanna, A.S. [Indian Inst. of Technology, Bombay (India)

    2008-07-01

    Pipeline integrity management is defined as a process for assessing and mitigating pipeline risks in an effort to reduce both the likelihood and consequences of incidents. Defects on pipelines result in production losses, environmental losses, as well as loss of goodwill and subsequent financial losses. This presentation addressed pipeline integrity through cathodic protection. It noted that pipeline integrity can be strengthened by successfully controlling, monitoring and mitigating corrosion strategies. It can also be achieved by avoiding external and internal corrosion failures. A good coating offers the advantages of low current density; lower power consumption; low wear of anodes; larger spacing between cathodic protection stations; and minimization of interference problems. The presentation reviewed cathodic protection of cross-country pipelines; a sacrificial cathodic protection system; and an impressed current cathodic protection system. The efficiency of a cathodic system was shown to depend on the use of reliable power sources; proper protection criterion; efficient and effective monitoring of cathodic protection; proper maintenance of the cathodic protection system; and effective remedial measures. Selection criteria, power sources, and a comparison of cathodic protection sources were also presented. Last, the presentation addressed protection criteria; current interruption circuits; monitoring of the cathodic protection system; use of corrosion coupons; advantages of weightless coupons; checking the insulating flanges for shorted bolts; insulated/short casings; anodic and cathodic interference; common corridor problems; and intelligent pigging. tabs., figs.

  1. Effect of the semi-conductive properties of the passive layer on the current provided by stainless steel microbial cathodes

    International Nuclear Information System (INIS)

    Geobacter sulfurreducens biofilms were formed under constant polarisation at -0.6 V vs. Ag/AgCl on stainless steel cathodes to catalyse the reduction of fumarate. The time-evolution of the current strongly depended on the quality of the inoculum. Inoculating with young cells significantly shortened the initial lag-phase and using the same inoculum improved the reproducibility of the current-time curves. The whole set of experiments showed that 254SMO stainless steel provided higher current densities (on average 14.1 A/m2) than biofilms formed on 316L stainless steel (on average 4.5 A/m2). Biofilm coverage assessed by epifluorescent microscopy showed that coverage ratios were generally higher for 316L than for 254SMO. It must be concluded that 254SMO is more efficient in transferring electrons to bacterial cells than 316L. Mott-Schottky diagrams recorded on both materials under conditions of electrolysis in the absence of microorganisms showed that the surface oxide layers had similar n-type semi-conductive behaviour for potential values higher than the flat band potential. In contrast, 316L exhibited slight p-type behaviour at potential lower than the flat band potential, while 254SMO did not. The higher electrochemical performances of biocathodes formed on 254SMO are explained by semi-conductive properties of its passive layer, which prevented the p-type behaviour occurring in cathodic electrolysis conditions.

  2. Effect of the semi-conductive properties of the passive layer on the current provided by stainless steel microbial cathodes

    Energy Technology Data Exchange (ETDEWEB)

    Pons, Liz; Delia, Marie-Line; Basseguy, Regine [Laboratoire de Genie Chimique, CNRS - Universite de Toulouse, 4 allee Emile Monso BP 84234, 31030 Toulouse (France); Bergel, Alain, E-mail: alain.bergel@ensiacet.f [Laboratoire de Genie Chimique, CNRS - Universite de Toulouse, 4 allee Emile Monso BP 84234, 31030 Toulouse (France)

    2011-02-15

    Geobacter sulfurreducens biofilms were formed under constant polarisation at -0.6 V vs. Ag/AgCl on stainless steel cathodes to catalyse the reduction of fumarate. The time-evolution of the current strongly depended on the quality of the inoculum. Inoculating with young cells significantly shortened the initial lag-phase and using the same inoculum improved the reproducibility of the current-time curves. The whole set of experiments showed that 254SMO stainless steel provided higher current densities (on average 14.1 A/m{sup 2}) than biofilms formed on 316L stainless steel (on average 4.5 A/m{sup 2}). Biofilm coverage assessed by epifluorescent microscopy showed that coverage ratios were generally higher for 316L than for 254SMO. It must be concluded that 254SMO is more efficient in transferring electrons to bacterial cells than 316L. Mott-Schottky diagrams recorded on both materials under conditions of electrolysis in the absence of microorganisms showed that the surface oxide layers had similar n-type semi-conductive behaviour for potential values higher than the flat band potential. In contrast, 316L exhibited slight p-type behaviour at potential lower than the flat band potential, while 254SMO did not. The higher electrochemical performances of biocathodes formed on 254SMO are explained by semi-conductive properties of its passive layer, which prevented the p-type behaviour occurring in cathodic electrolysis conditions.

  3. A High-Gradient CW R Photo-Cathode Electron Gun for High Current Injectors

    Energy Technology Data Exchange (ETDEWEB)

    Robert Rimmer

    2005-05-01

    The paper describes the analysis and preliminary design of a high-gradient photo-cathode RF gun optimized for high current CW operation. The gun cell shape is optimized to provide maximum acceleration for the newly emitted beam while minimizing wall losses in the structure. The design is intended for use in future high-current high-power CW FELs but the shape optimization for low wall losses may be advantageous for other applications such as XFELs or Linear Colliders using high peak power low duty factor guns where pulse heating is a limitation. The concept allows for DC bias on the photocathode in order to repel ions and improve cathode lifetime.

  4. Evolution of oxygen reduction current and biofilm on stainless steels cathodically polarised in natural aerated seawater

    International Nuclear Information System (INIS)

    The aim of a series of works recently performed at ISMAR was to provide new useful information for a better understanding of the mechanisms by which bacteria settlement causes corrosion on Stainless Steels (SS) and similar active-passive alloys exposed to seawater. In this work, the evolutions of cathodic current, bacteria population, and electronic structure of the passive layer were investigated on SS samples polarised at fixed potentials during their exposure to natural seawater. It was found that, during the first phase of biofilm growth, cathodic current increase is proportional to the number of settled bacteria at each fixed potential. However, the proportionality factor between settled bacteria and cathodic current depends on imposed potential. In particular, the proportionality factor strongly decreases when the potential is increased above a critical value close to -150 mV Ag/AgCl. This effect seems to be correlated with the electronic structure of the passive layer. Indeed, the outer part of the passive layer on tested SS was found to behave like a conductor at potentials more active than -150 mV Ag/AgCl, and like an n-type semiconductor at more noble potentials

  5. Examination of ionic wind and cathode sheath effects in a E-field premixed flame with ion density measurements

    Science.gov (United States)

    Jacobs, Stewart V.; Xu, Kunning G.

    2016-04-01

    The effect of the ionic wind on a premixed methane-air flame under a DC electric field is studied via mapping of the ion density with Langmuir probes. Ion densities were observed to increase near the burner with increasing electrode voltage up to 6 kV. Past this electrode supply voltage, ion densities ceased increasing and began to decline in some locations within the premixed flame. The increased ion density is caused by an increase in ionic wind force and cathode sheath thickness. The plateau in density is due to the cathode sheath fully encompassing the flame front which is the ion source, thereby collecting all ions in the flame. The spatial density data support the ionic wind hypothesis and provide further explanation of its limits based on the plasma sheath.

  6. Synthesis of thick diamond films by direct current hot-cathode plasma chemical vapour deposition

    CERN Document Server

    Jin Zeng Sun; Bai Yi Zhen; Lu Xian Yi

    2002-01-01

    The method of direct current hot-cathode plasma chemical vapour deposition has been established. A long-time stable glow discharge at large discharge current and high gas pressure has been achieved by using a hot cathode in the temperature range from 1100 degree C to 1500 degree C and non-symmetrical configuration of the poles, in which the diameter of the cathode is larger than that of anode. High-quality thick diamond films, with a diameter of 40-50 mm and thickness of 0.5-4.2 mm, have been synthesized by this method. Transparent thick diamond films were grown over a range of growth rates between 5-10 mu m/h. Most of the thick diamond films have thermal conductivities of 10-12 W/K centre dot cm. The thick diamond films with high thermal conductivity can be used as a heat sink of semiconducting laser diode array and as a heat spreading and isolation substrate of multichip modules. The performance can be obviously improved

  7. Development of Magnetic Hollow Cold Cathode for Ion Source

    OpenAIRE

    Djamel Boubetra; Bouafia, M.

    2008-01-01

    The research presented in this study focuses on the development of ion source with hollow cold cathodes which supplies low-power and high ion-current density applications. The theoretical and experimental results were used to design a second-generation laboratory model, low-current hollow cathode. Present experiment is to design a hollow cold cathode with two application possibilities.

  8. Theoretical model and experimental investigation of current density boundary condition for welding arc study

    Science.gov (United States)

    Boutaghane, A.; Bouhadef, K.; Valensi, F.; Pellerin, S.; Benkedda, Y.

    2011-04-01

    This paper presents results of theoretical and experimental investigation of the welding arc in Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) processes. A theoretical model consisting in simultaneous resolution of the set of conservation equations for mass, momentum, energy and current, Ohm's law and Maxwell equation is used to predict temperatures and current density distribution in argon welding arcs. A current density profile had to be assumed over the surface of the cathode as a boundary condition in order to make the theoretical calculations possible. In stationary GTAW process, this assumption leads to fair agreement with experimental results reported in literature with maximum arc temperatures of ~21 000 K. In contrast to the GTAW process, in GMAW process, the electrode is consumable and non-thermionic, and a realistic boundary condition of the current density is lacking. For establishing this crucial boundary condition which is the current density in the anode melting electrode, an original method is setup to enable the current density to be determined experimentally. High-speed camera (3000 images/s) is used to get geometrical dimensions of the welding wire used as anode. The total area of the melting anode covered by the arc plasma being determined, the current density at the anode surface can be calculated. For a 330 A arc, the current density at the melting anode surface is found to be of 5 × 107 A m-2 for a 1.2 mm diameter welding electrode.

  9. Effect of cathode and anode plasma motion on current characteristics of pinch diode

    International Nuclear Information System (INIS)

    The preliminary research results for the effect of cathode and anode plasma motion on current characteristics of the pinch ion diode on FLASH II accelerator are reported. The structure and principle of pinch reflex ion beam diode are introduced. The time dependent evolution of electron and ion flow in large aspect-ratio relativistic diodes is studied by analytic models. The equation of Child-langmuir, weak focused-flow, strong focused-flow and parapotential flow are corrected to reduce the diode A-C gap caused by the motion of cathode and anode plasma. The diode current and ion current are calculated with these corrected equations, and the results are consistent with the experimental data. The methods of increasing ion current and efficiency are also presented. The high power ion beam peak current about 160 kA with a peak energy about 500 keV was produced using water-dielectric transmission-line generators with super-pinch reflex ion diodes on FLASH II accelerator at Northwest Institute of Nuclear Technology (NINT). (authors)

  10. CdS-metal contact at higher current densities.

    Science.gov (United States)

    Stirn, R. J.; Boeer, K. W.; Dussel, G. A.

    1973-01-01

    An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.

  11. Anode current density distribution in a cusped field thruster

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Huan, E-mail: wuhuan58@qq.com; Liu, Hui, E-mail: hlying@gmail.com; Meng, Yingchao; Zhang, Junyou; Yang, Siyu; Hu, Peng; Chen, Pengbo; Yu, Daren [Mail Box 458, Harbin Institute of Technology (HIT), Harbin 150001 (China)

    2015-12-15

    The cusped field thruster is a new electric propulsion device that is expected to have a non-uniform radial current density at the anode. To further study the anode current density distribution, a multi-annulus anode is designed to directly measure the anode current density for the first time. The anode current density decreases sharply at larger radii; the magnitude of collected current density at the center is far higher compared with the outer annuli. The anode current density non-uniformity does not demonstrate a significant change with varying working conditions.

  12. Cathode performance during two beam operation of the high current high polarization electron gun for eRHIC

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, O. [Brookhaven National Lab. (BNL), Upton, NY (United States); Ben-Zvi, I. [Brookhaven National Lab. (BNL), Upton, NY (United States); Degen, C. [Brookhaven National Lab. (BNL), Upton, NY (United States); Gassner, D. M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Lambiase, R. [Brookhaven National Lab. (BNL), Upton, NY (United States); Meng, W. [Brookhaven National Lab. (BNL), Upton, NY (United States); Pikin, A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Rao, T. [Brookhaven National Lab. (BNL), Upton, NY (United States); Sheehy, B. [Brookhaven National Lab. (BNL), Upton, NY (United States); Skaritka, J. [Brookhaven National Lab. (BNL), Upton, NY (United States); Wang, E. [Brookhaven National Lab. (BNL), Upton, NY (United States); Pietz, J. [Transfer Engineering and Manufacturing, Inc., Fremont, CA (United States); Ackeret, M. [Transfer Engineering and Manufacturing, Inc., Fremont, CA (United States); Yeckel, C. [Stangenes Industries, Palo Alto, CA (United States); Miller, R. [Stangenes Industries, Palo Alto, CA (United States); Dobrin, E. [Stangenes Industries, Palo Alto, CA (United States); Thompson, K. [Stangenes Industries, Palo Alto, CA (United States)

    2015-05-03

    Two electron beams from two activated bulk GaAs photocathodes were successfully combined during the recent beam test of the High Current High Polarization Electron gun for eRHIC. The beam test took place in Stangenes Industries in Palo Alto, CA, where the cathodes were placed in diagonally opposite locations inside the high voltage shroud. No significant cross talking between the cathodes was found for the pertinent vacuum and low average current operation, which is very promising towards combining multiple beams for higher average current. This paper describes the cathode preparation, transport and cathode performance in the gun for the combining test, including the QE and lifetimes of the photocathodes at various steps of the experiment.

  13. Cathode performance during two beam operation of the high current high polarization electron gun for eRHIC

    International Nuclear Information System (INIS)

    Two electron beams from two activated bulk GaAs photocathodes were successfully combined during the recent beam test of the High Current High Polarization Electron gun for eRHIC. The beam test took place in Stangenes Industries in Palo Alto, CA, where the cathodes were placed in diagonally opposite locations inside the high voltage shroud. No significant cross talking between the cathodes was found for the pertinent vacuum and low average current operation, which is very promising towards combining multiple beams for higher average current. This paper describes the cathode preparation, transport and cathode performance in the gun for the combining test, including the QE and lifetimes of the photocathodes at various steps of the experiment.

  14. Electron beam induced current measurement on a specimen biased in a cathode lens

    Czech Academy of Sciences Publication Activity Database

    Horáček, Miroslav; Zobač, Martin; Vlček, Ivan

    Graz : Verlag der Technischen Universität, 2009, Vol. 1: 211-212. ISBN 978-3-85125-062-6. [MC 2009 - Joint Meeting of Dreiländertagung and Multinational Congress on Microscopy /9./. Graz (AT), 30.08.2009-04.09.2009] R&D Projects: GA AV ČR IAA100650803 Institutional research plan: CEZ:AV0Z20650511 Keywords : elektron beam induced current * SEM * very low energy electrons * cathode lens * specimen bias Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering http://www.univie.ac.at/asem/Graz_MC_09/papers/77645.pdf

  15. Humectants To Augment Current From Metallized Zinc Cathodic Protection Systems on Concrete

    Energy Technology Data Exchange (ETDEWEB)

    Holcomb, Gordon R.; Covino Jr., Bernard S.; Cramer, Stephen D.; Russell, James H. Russell; Bullard, Sophie J.; Collins, W. Keith; Bennett, Jack E. (J.E. Bennett Consulting, Inc.); Soltesz, Steven M. (ODOT); Laylor, H. Martin (ODOT)

    2002-12-01

    Cathodic protection (CP) systems using thermal-sprayed zinc anodes are employed to mitigate the corrosion process in reinforced concrete structures. However, the performance of the anodes is improved by moisture at the anode-concrete interface. Research was conducted to investigate the effect of hydrophilic chemical additives, humectants, on the electrical performance and service life of zinc anodes. Lithium bromide and lithium nitrate were identified as feasible humectants with lithium bromide performing better under galvanic CP and lithium nitrate performing better under impressed current CP. Both humectants improved the electrical operating characteristics of the anode and increased the service life by up to three years.

  16. Lithium Sulfur Primary Battery with Super High Energy Density: Based on the Cauliflower-like Structured C/S Cathode

    OpenAIRE

    Yiwen Ma; Hongzhang Zhang; Baoshan Wu; Meiri Wang; Xianfeng Li; Huamin Zhang

    2015-01-01

    The lithium-sulfur primary batteries, as seldom reported in the previous literatures, were developed in this work. In order to maximize its practical energy density, a novel cauliflower-like hierarchical porous C/S cathode was designed, for facilitating the lithium-ions transport and sulfur accommodation. This kind of cathode could release about 1300 mAh g−1 (S) capacity at sulfur loading of 6 ~ 14 mg cm−2, and showed excellent shelf stability during a month test at room temperature. As a res...

  17. Effects of discharge current and voltage on the high density of metastable helium atoms

    Institute of Scientific and Technical Information of China (English)

    Feng Xian-Ping(冯贤平); D Andruczyk; B W James; K Takiyama; S Namba; T Oda

    2003-01-01

    Both hollow-cathode and Penning-type discharges were adopted to excite helium atoms to a metastable state.Experimental data indicate that Penning discharge is more suitable for generating high fractions of metastables in a low-density helium beam for laser-induced fluorescence technique in measuring electric fields at the edge of a plasma.The metastable density increases with increasing helium gas pressure in the range of 1.33× 10-2-66.7Pa. The highest metastable density of 3.8 × 1016m-3 is observed at a static gas pressure of 66.7Pa. An approximately linear relationship between the density of metastable helium atoms and the plasma discharge current is observed. Magnetic field plays a very important role in producing a high density of metastable atoms in Penning discharge.

  18. Effects of discharge current and voltage on the high density of metastable helium atoms

    Institute of Scientific and Technical Information of China (English)

    FengXian-Ping; DAndruczyk; BWJames; KTakiyama; SNamba; TOda

    2003-01-01

    Both hollow-cathode and Penning-type discharges were adopted toexcite helium atoms to a metastable state. Experimental data indicate that Penning discharge is more suitable for generating high fractions of metastables in a low-density helium hean for laser-induced fluorescence technique in measuring electric fields at the edge of a plasma. The metastable density increases with increasing helium gas pressure in the range of 1.33×10-2-66.7Pa. The highest metastable density of 3.8×1016m-3 is observed at a static gas pressure of 66.7Pa. An approximately linear relationship between the density of metastable helium atoms and the plasma discharge current is observed. Magnetic field plays a very important role in producing a high density of metastable atoms in Penning discharge.

  19. High-density and low electron temperature direct current reflex plasma source

    International Nuclear Information System (INIS)

    A new type of direct current, high-density, and low electron temperature reflex plasma source, obtained as a hybrid between a modified hollow-cathode discharge and a Penning ionization gauge discharge is presented. The plasma source was tested in argon, nitrogen, and oxygen over a range pressure of 1.0-10-3 m-bar, discharge currents 20-200 mA, and magnetic field 0-120 Gauss. Both external parameters, such as breakdown potential and the discharge voltage-current characteristic, and its internal parameters, like the electron energy distribution function, electron and ion densities, and electron temperature, were measured. Due to the enhanced hollow-cathode effect by the magnetic trapping of electrons, the density of the bulk plasma is as high as 1018 m-3, and the electron temperature is as low as a few tenths of electron volts. The plasma density scales with the dissipated power. Another important feature of this reflex plasma source is its high degree of uniformity, while the discharge bulk region is free of an electric field

  20. Time dependant quantum efficiency and dark current measurements in an RF photocathode injector with a high quantum efficiency cathode

    International Nuclear Information System (INIS)

    Studies of photo-emission and field emission behavior in an RF gun have been carried out. Unexpected phenomena were observed. In situ changes in the cathode's quantum efficiency and dark current with time were seen during operation of the photo-injector. These changes were correlated with the magnetostatic field at the cathode. In addition, multipacting has been observed under certain conditions. Recent measurements indicate a correlation between multipacting and anomalous photo- and field emission behavior

  1. Hollow cathode hydrogen ion source

    International Nuclear Information System (INIS)

    High current density ion sources have been used to heat plasmas in controlled thermonuclear reaction experiments. High beam currents imply relatively high emission currents from cathodes which have generally taken the form of tungsten filaments. This paper describes a hydrogen ion source which was primarily developed to assess the emission current capability and design requirements for hollow cathodes for application in neutral injection devices. The hydrogen source produced ions by electron bombardment via a single hollow cathode. Source design followed mercury ion thruster technology, using a weak magnetic field to enhance ionization efficiency. A 1.3-cm diameter hollow cathode using a low work function material dispenser performed satisfactorily over a discharge current range of 10 to 90 A. Cylindrical probe measurements taken without ion extraction indicate maximum ion number densities on the order of 1012 cm-3. Discharge durations ranged from 30 seconds to continuous operation. Tests with beam extraction at 2.5 keV and 30 A discharge current yield average ion beam current densities of 0.1 A cm-2 over a 5-cm extraction diameter. Results of this study can be used to supply the baseline information needed to scale hollow cathodes for operation at discharge currents of hundreds of amperes using distributed cathodes

  2. A new dispenser cathode with dual-layer

    Science.gov (United States)

    Li, Yutao; Zhang, Honglai; Liu, Pukun; Zhang, Mingchen

    2005-09-01

    The emission and surface characteristics of the dispenser cathode coated with Os-W alloy and that coated with Os-W/Re are studied and compared. The dispenser cathode coated with Os-W/Re has been applied in electron gun measurement system for making measurement of higher emission current and life test. We called the cathode coated with Os-W/Re as the cathode with dual-layer. It is found that the dispenser cathode coated with dual-layer has higher current density than that coated only with Os-W alloy. After being activated, the cathode coated with dual-layer presents ternary composition on the surface of it. The W surface composition does not rise with time comparing with that of the cathode coated with Os-W alloy. In electron gun, the dispenser cathode coated with dual-layer has pulse current density of 30 A/cm 2 and life of more than 800 h.

  3. A new dispenser cathode with dual-layer

    International Nuclear Information System (INIS)

    The emission and surface characteristics of the dispenser cathode coated with Os-W alloy and that coated with Os-W/Re are studied and compared. The dispenser cathode coated with Os-W/Re has been applied in electron gun measurement system for making measurement of higher emission current and life test. We called the cathode coated with Os-W/Re as the cathode with dual-layer. It is found that the dispenser cathode coated with dual-layer has higher current density than that coated only with Os-W alloy. After being activated, the cathode coated with dual-layer presents ternary composition on the surface of it. The W surface composition does not rise with time comparing with that of the cathode coated with Os-W alloy. In electron gun, the dispenser cathode coated with dual-layer has pulse current density of 30 A/cm2 and life of more than 800 h

  4. Compact High Current Rare-Earth Emitter Hollow Cathode for Hall Effect Thrusters

    Science.gov (United States)

    Hofer, Richard R. (Inventor); Goebel, Dan M. (Inventor); Watkins, Ronnie M. (Inventor)

    2012-01-01

    An apparatus and method for achieving an efficient central cathode in a Hall effect thruster is disclosed. A hollow insert disposed inside the end of a hollow conductive cathode comprises a rare-earth element and energized to emit electrons from an inner surface. The cathode employs an end opening having an area at least as large as the internal cross sectional area of the rare earth insert to enhance throughput from the cathode end. In addition, the cathode employs a high aspect ratio geometry based on the cathode length to width which mitigates heat transfer from the end. A gas flow through the cathode and insert may be impinged by the emitted electrons to yield a plasma. One or more optional auxiliary gas feeds may also be employed between the cathode and keeper wall and external to the keeper near the outlet.

  5. Current-voltage curve of a bipolar membrane at high current density

    NARCIS (Netherlands)

    Aritomi, T.; Boomgaard, van den Th.; Strathmann, H.

    1996-01-01

    The potential drop across a bipolar membrane was measured as a function of the applied current density. As a result, an inflection point was observed in the obtained current-voltage curve at high current density. This inflection point indicates that at high current densities water supply from outsid

  6. Current Developments in Nuclear Density Functional Methods

    OpenAIRE

    Dobaczewski, J.

    2010-01-01

    Density functional theory (DFT) became a universal approach to compute ground-state and excited configurations of many-electron systems held together by an external one-body potential in condensed-matter, atomic, and molecular physics. At present, the DFT strategy is also intensely studied and applied in the area of nuclear structure. The nuclear DFT, a natural extension of the self-consistent mean-field theory, is a tool of choice for computations of ground-state properties and low-lying exc...

  7. The investigation of carbon nitride films prepared at various arc currents by vacuum cathode arc method

    International Nuclear Information System (INIS)

    The carbon nitride films have been prepared in the arc currents range of 20-60 A at the Ar/N2 atmosphere of 50/400 sccm by the vacuum cathode arc deposition method. The properties of the films were characterized by x-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and nanoindentation. The N concentration showed a maximum of 35 at% at 20 A and decreased gradually with the arc currents. The films below 40 A consisted of linear polymeric-like component and sp2 graphitic cluster. With the increasing of the arc current from 20 to 40 A, the ID/IG rose and the photoluminescence (PL) fell gradually, which resulted from the development of the sp2 graphitic phase and the decrease of the polymeric-like phase. As a result, the CC bonds increased and sp3CN and sp2CN decreased. Above 40 A, with the increasing of arc currents, ID/IG fell and the PL increased gradually, which reflected the decreasing of sp2 graphitic phase and the modification of C and N atoms in sp2 cluster. The CC bonds and sp3CN fell and the sp2CN rose. The nanohardness of films showed increasing tendency with the arc currents. The variation of the relative ratio and the average energy of N-containing species and C-containing species at the atmosphere would be responsible for the change in the properties of films. (author)

  8. Limiting current density and water dissociation in bipolar membranes

    NARCIS (Netherlands)

    Strathmann, H.; Krol, J.J.; Rapp, H.-J.; Eigenberger, G.

    1997-01-01

    The behaviour of bipolar membranes in NaCl and Na2SO4 solutions is discussed. The membranes are characterized in terms of their limiting current densities. Below the limiting current density the electric current is carried by salt ions migrating from the transition region between the anion and the c

  9. Electrodeposition from cationic cuprous organic complexes: Ionic liquids for high current density electroplating

    OpenAIRE

    Schaltin, Stijn; Brooks, Neil; Binnemans, Koen; Fransaer, Jan

    2011-01-01

    The electrochemical behavior of the low-melting copper salts [Cu(MeCN)(x)][Tf2N] and [Cu(PhCN)(x)][Tf2N] (x = 2-4), where MeCN is acetonitrile and PhCN is benzonitrile, is presented. In these compounds, the copper(I) ion is a main component of the ionic liquid cation. Consequently, the copper concentration is the highest achievable for an ionic liquid and this permits to obtain a good mass transport and high current densities for electrodeposition. The cathodic limit of the ionic liquid is th...

  10. Current control of the electron beam formed in the magnetron gun with a secondary-emission cathode

    International Nuclear Information System (INIS)

    Data are reported on electron beam generation and beam current control in two types of secondary-emission cathode magnetron guns. The influence of the magnetic field value and field distribution on the formation of the beam and its parameters has been investigated in the electron energy range between 20 and 150 keV. The influence of local magnetic field variations on the cathode and the electron beam characteristics has been studied. The possibility to control the electron beam current in various ways has been demonstrated

  11. Current Source Density Estimation for Single Neurons

    Directory of Open Access Journals (Sweden)

    Dorottya Cserpán

    2014-03-01

    Full Text Available Recent developments of multielectrode technology made it possible to measure the extracellular potential generated in the neural tissue with spatial precision on the order of tens of micrometers and on submillisecond time scale. Combining such measurements with imaging of single neurons within the studied tissue opens up new experimental possibilities for estimating distribution of current sources along a dendritic tree. In this work we show that if we are able to relate part of the recording of extracellular potential to a specific cell of known morphology we can estimate the spatiotemporal distribution of transmembrane currents along it. We present here an extension of the kernel CSD method (Potworowski et al., 2012 applicable in such case. We test it on several model neurons of progressively complicated morphologies from ball-and-stick to realistic, up to analysis of simulated neuron activity embedded in a substantial working network (Traub et al, 2005. We discuss the caveats and possibilities of this new approach.

  12. Current Density and Plasma Displacement Near Perturbed Rational Surface

    International Nuclear Information System (INIS)

    The current density in the vicinity of a rational surface of a force-free magnetic field subjected to an ideal perturbation is shown to be the sum of both a smooth and a delta-function distribution, which give comparable currents. The maximum perturbation to the smooth current density is comparable to a typical equilibrium current density and the width of the layer in which the current flows is shown to be proportional to the perturbation amplitude. In the standard linearized theory, the plasma displacement has an unphysical jump across the rational surface, but the full theory gives a continuous displacement.

  13. Miniature Reservoir Cathode: An Update

    Science.gov (United States)

    Vancil, Bernard K.; Wintucky, Edwin G.

    2002-01-01

    We report on recent work to produce a small low power, low cost reservoir cathode capable of long life (more than 100,000 hours) at high loading (> 5 A/sq cm). Our objective is a highly manufacturable, commercial device costing less than $30. Small highly loaded cathodes are needed, especially for millimeter wave tubes, where focusing becomes difficult when area convergence ratios are too high. We currently have 3 models ranging from .060-inch diameter to. 125-inch diameter. Reservoir type barium dispenser cathodes have a demonstrated capability for simultaneous high emission density and long life. Seven reservoir cathodes continue to operate on the cathode life test facility at NSWC, Crane, Indiana at 2 and 4 amps/sq cm. They have accumulated nearly 100,000 hours with practically no change in emission levels or knee temperature.

  14. Analysing bifurcations encountered in numerical modelling of current transfer to cathodes of dc glow and arc discharges

    Energy Technology Data Exchange (ETDEWEB)

    Almeida, P G C; Benilov, M S; Cunha, M D; Faria, M J [Departamento de Fisica, Universidade da Madeira, Largo do Municipio, 9000 Funchal (Portugal)

    2009-10-07

    Bifurcations and/or their consequences are frequently encountered in numerical modelling of current transfer to cathodes of gas discharges, also in apparently simple situations, and a failure to recognize and properly analyse a bifurcation may create difficulties in the modelling and hinder the understanding of numerical results and the underlying physics. This work is concerned with analysis of bifurcations that have been encountered in the modelling of steady-state current transfer to cathodes of glow and arc discharges. All basic types of steady-state bifurcations (fold, transcritical, pitchfork) have been identified and analysed. The analysis provides explanations to many results obtained in numerical modelling. In particular, it is shown that dramatic changes in patterns of current transfer to cathodes of both glow and arc discharges, described by numerical modelling, occur through perturbed transcritical bifurcations of first- and second-order contact. The analysis elucidates the reason why the mode of glow discharge associated with the falling section of the current-voltage characteristic in the solution of von Engel and Steenbeck seems not to appear in 2D numerical modelling and the subnormal and normal modes appear instead. A similar effect has been identified in numerical modelling of arc cathodes and explained.

  15. Evidence of the Current Collector Effect: Study of the SOFC Cathode Material Ca3Co4O9+d

    NARCIS (Netherlands)

    Rolle, A.; Thoréton, V.; Rozier, P.; Capoen, E.; Mentré, O.; Boukamp, B.A.; Daviero-Minaud, S.

    2012-01-01

    In the study of the performance of solid oxide fuel cell (SOFC) electrodes, the possible influence of the applied current collector is often not mentioned or recognized. In this article, as part of an optimization study of the potentially attractive Ca3Co4O9+δ cathode material (Ca349), special atten

  16. Effect of current density on the morphology of Zn electrodeposits

    Institute of Scientific and Technical Information of China (English)

    Ailing Fan; Wenhuai Tian; M. Kurosaki

    2004-01-01

    The effect of current density on the morphology of Zn electrodeposits prepared by a flow-channel cell was investigated by scanning electron microscopy (SEM). It was found that the morphology of Zn electrodeposits evolves from thin-layered hexagonal η-phase crystals to pyramidal η-phase particles with increasing the current density. The morphological evolution at various flow rates was also examined and the results show that the morphological evolution at a lower flow rate is more remarkable than that at a higher flow rate with increasing the current density. To reveal the mechanism of the morphological evolution in detail, the atomic configuration on both (0001)η and { 1100 }η planes under different current densities was investigated, it was noted that a specify current density could provide a good condition for the layered epitaxial growth of hexagonal η-phase.

  17. Field dependence of critical current density in flat superconductor

    International Nuclear Information System (INIS)

    Surface field of a thin superconductor YBa2Cu3O7-δ in mixed state is measured by a Hall probe array. To reproduce the measured field profiles, shielding current distributions are determined by numerical iterative calculations without supposing any models for field dependence of critical current density Jc (B). Utilizing the estimated local current density and local magnetic field for x - y coordinates, a field variation of current density is plotted. Though any model for Jc (B) is not used for numerical calculations, the field variation roughly shows a dependence like Kim model.

  18. Vertically aligned carbon nanotube electrodes for high current density operating proton exchange membrane fuel cells

    Science.gov (United States)

    Murata, Shigeaki; Imanishi, Masahiro; Hasegawa, Shigeki; Namba, Ryoichi

    2014-05-01

    We successfully developed cathode electrodes for polymer electrolyte membrane fuel cells (PEMFC) that enable operation at high current densities by incorporating vertically aligned carbon nanotubes (CNTs) as the catalyst support; additionally, we prepared 236 cm2 membrane electrodes assemblies (MEAs) for vehicular use. The electrode structure improved the mass transport of reactants, i.e. oxygen, proton, electron and water, in systems performing at a 2.6 A cm-2 current density and 0.6 V with extremely low platinum (Pt) loading at the cathode (0.1 mg cm-2). The improved mass transport caused the 70 mV dec-1 Tafel slope to continue up to 1.0 A cm-2. The mass transport was improved because the pores were continuous, the catalyst support materials did not agglomerate and the catalyst layer made good electrical contact with the microporous layer. Utilizing wavy coil-shaped CNTs was also crucial. These CNTs displayed anti-agglomerative characteristics during the wet manufacturing process and maintained a continuous pore structure framing the layered catalyst structure. Because the CNTs had elastic characteristics, they might fill the space between catalyst and microporous layers to prevent flooding. However, the compressed CNTs in the cells were no longer vertically aligned. Therefore, vertically aligning the nanotubes was important during the MEA manufacturing process but was irrelevant for cell performance.

  19. Exchange current model for (La0.8Sr0.2)0.95MnO3 (LSM) porous cathode for solid oxide fuel cells

    Science.gov (United States)

    Miyoshi, Kota; Miyamae, Takuma; Iwai, Hiroshi; Saito, Motohiro; Kishimoto, Masashi; Yoshida, Hideo

    2016-05-01

    In this paper, we propose an empirical formula for i0,TPB, the exchange current density per unit triple-phase boundary (TPB) length, for porous lanthanum strontium manganite (LSM) cathodes of solid oxide fuel cells (SOFCs); the evaluation of i0,TPB is of crucial importance in numerical simulations of electrodes based on reconstructed microstructures obtained by a dual beam focused ion beam scanning electron microscopy (FIB-SEM) and tomography techniques. To derive a widely applicable empirical formula for i0,TPB, electrochemical measurements of porous LSM cathodes are conducted under various oxygen partial pressures (0.05-0.25 atm) and temperatures (800-950 °C). By comparing the derived formula with that derived from a thin and dense patterned LSM electrode used in previous studies, it is found that at an air temperature of 800 °C, i0,TPB derived from a porous LSM cathode is approximately 40% smaller than that for the patterned electrode. This can be attributed to the fact that the electrochemical reaction in thin and dense electrodes can occur not only at the TPBs but also at the LSM surface owing to the non-negligible ionic conductivity of LSM. The derived formula is also applied to a three-dimensional numerical simulation to confirm its validity.

  20. Self protection of high current density superconducting magnets

    International Nuclear Information System (INIS)

    Light weight magnets are required for space borne application and for mobile systems such as tanks and ships. To reduce system weight high current density conductors have to be utilized. Two schemes are proposed for magnet protection. A self protection scheme for high current density conductors using metallic structure such as beryllium to act as a transformer secondary whereas the conductor winding acting as the primary. A dump resistor is proposed as the second protection scheme for comparison. It requires the use of lightweight high temperature dump resistor but the current density will be limited to 10 to 15 kA/cm/sup 2/

  1. Electrochemical Properties of Boron-Doped Diamond Electrodes Prepared by Hot Cathode Direct Current Plasma CVD

    Directory of Open Access Journals (Sweden)

    Hong Yan PENG

    2016-05-01

    Full Text Available A series of boron-doped diamond (BDD films were deposited by using a hot cathode direct current plasma chemical vapor deposition(HCDC-PCVD system with different ratios of CH4/H2/B(OCH33 (trimethylborate gas mixture. The morphology, structure and quality of BDD films were controled by SEM, XRD and Raman measurements. The electrochemical properties of the BDD films were investigated by electrochemical methods. Cyclic voltammetric performances of the BDD films indicated that the main determinant in the electrochemical characteristics of BDD films was the boron doping amount. The threshold potential for oxygen evolution increased from 1 V to 2.5 V. Meanwhile, the electrochemical potential window of BDD films was enlarged from 2.2 V to 4.5 V when the B content was increased from 1.75 × 1019cm-3 to 2.4 × 1021 cm−3. The cyclic voltammograms of BDD films in K4Fe(CN6 and K3Fe(CN6 mixed solution indicated that the behavior of Fe(CN6-3/-4 redox couple could be regarded as semi-reversible.DOI: http://dx.doi.org/10.5755/j01.ms.22.2.12926

  2. Density changes with substrate negative bias for ta-C films deposited by filter cathode vacuum arc

    Institute of Scientific and Technical Information of China (English)

    TAN Man-lin; ZHU Jia-qi; HAN Jie-cai; MENG Song-he

    2004-01-01

    Specular X-ray reflectivity (XRR) measurements were used to study the density and cross-section information of tetrahedral amorphous carbon (ta-C) films deposited by filter cathode vacuum arc(FCVA) system at different substrate bias. According to the correlation between density and substrate negative bias, it is found that the value of density reaches a maximum at -80 V bias. As the substrate bias increases or decreases, the density tends to lower gradually. Based on the density of diamond and graphite, sp3 bonding ratio of ta-C films was obtained from their corresponding density according to a simple equation between the two. And a similar parabolic variation was observed for ta-C films with the sp3 content changes with substrate negative bias. The mechanical properties such as hardness and elastic modulus were also measured and compared with the corresponding density for ta-C films. From the distribution of data points, a linear proportional correlation between them was found, which shows that the density is a critical parameter to characterize the structure variation for ta-C films.

  3. High current densities enable exoelectrogens to outcompete aerobic heterotrophs for substrate

    KAUST Repository

    Ren, Lijiao

    2014-08-05

    © 2014 Wiley Periodicals, Inc. Chemical oxygen demand (COD) removal rates could be described by first-order kinetics with respect to COD concentration at different current densities, even under open circuit conditions with no current generation. The COD concentration was reduced more quickly with current generation due to the greater consumption of substrate by exoelectrogens, and less substrate was lost to aerobic heterotrophs. Higher current densities enabled exoelectrogens to outcompete aerobic heterotrophs for substrate, allowing for increased coulombic efficiencies with current densities. © 2014 Wiley Periodicals, Inc. In mixed-culture microbial fuel cells (MFCs), exoelectrogens and other microorganisms compete for substrate. It has previously been assumed that substrate losses to other terminal electron acceptors over a fed-batch cycle, such as dissolved oxygen, are constant. However, a constant rate of substrate loss would only explain small increases in coulombic efficiencies (CEs, the fraction of substrate recovered as electrical current) with shorter cycle times, but not the large increases in CE that are usually observed with higher current densities and reduced cycle times. To better understand changes in CEs, COD concentrations were measured over time in fed-batch, single-chamber, air-cathode MFCs at different current densities (external resistances). COD degradation rates were all found to be first-order with respect to COD concentration, even under open circuit conditions with no current generation (first-order rate constant of 0.14±0.01h-1). The rate of COD removal increased when there was current generation, with the highest rate constant (0.33±0.02h-1) obtained at the lowest external resistance (100Ω). Therefore, as the substrate concentration was reduced more quickly due to current generation, the rate of loss of substrate to non-exoelectrogens decreased due to this first-order substrate-concentration dependence. As a result, coulombic

  4. High power microwave generation from coaxial virtual cathode oscillator using graphite and velvet cathodes

    Science.gov (United States)

    Menon, Rakhee; Roy, Amitava; Singh, S. K.; Mitra, S.; Sharma, Vishnu; Kumar, Senthil; Sharma, Archana; Nagesh, K. V.; Mittal, K. C.; Chakravarthy, D. P.

    2010-05-01

    High power microwave (HPM) generation studies were carried out in KALI-5000 pulse power system. The intense relativistic electron beam was utilized to generate HPMs using a coaxial virtual cathode oscillator. The typical electron beam parameters were 350 kV, 25 kA, and 100 ns, with a few hundreds of ampere per centimeter square current density. Microwaves were generated with graphite and polymer velvet cathode at various diode voltage, current, and accelerating gaps. A horn antenna setup with diode detector and attenuators was used to measure the microwave power. It was observed that the microwave power increases with the diode voltage and current and reduces with the accelerating gap. It was found that both the peak power and width of the microwave pulse is larger for the velvet cathode compared to the graphite cathode. In a coaxial vircator, velvet cathode is superior to the graphite cathode due to its shorter turn on time and better electron beam uniformity.

  5. Spectral Density of (Pseudo)Scalar Currents at Finite Temperature

    CERN Document Server

    Veliev, Elsen Veli; Sundu, Hayriye; Kaya, Gulsah

    2010-01-01

    We study the spectral densities of (pseudo)scalar currents at finite temperature in general case when mass of two quarks are different. Such spectral densities are necessary for the phenomenological investigation of hadronic parameters. We use quark propagator at finite temperature and show that an additional branch cut arises in spectral density, which corresponds to particle absorption from the medium. The obtained results at T \\rightarrow 0 limit are in good agreement with the vacuum results.

  6. Determining the Limiting Current Density of Vanadium Redox Flow Batteries

    Directory of Open Access Journals (Sweden)

    Jen-Yu Chen

    2014-09-01

    Full Text Available All-vanadium redox flow batteries (VRFBs are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential is affected by the electrolyte flow rate and electrolyte composition, which is related to the limiting current density. In order to investigate the effect of operating conditions on mass transport overpotential, this study established a relationship between the limiting current density and operating conditions. First, electrolyte solutions with different states of charge were prepared and used for a single cell to obtain discharging polarization curves under various operating conditions. The experimental results were then analyzed and are discussed in this paper. Finally, this paper proposes a limiting current density as a function of operating conditions. The result helps predict the effect of operating condition on the cell performance in a mathematical model.

  7. Nonlinear time-series analysis of current signal in cathodic contact glow discharge electrolysis

    Science.gov (United States)

    Allagui, Anis; Rojas, Andrea Espinel; Bonny, Talal; Elwakil, Ahmed S.; Abdelkareem, Mohammad Ali

    2016-05-01

    In the standard two-electrode configuration employed in electrolytic process, when the control dc voltage is brought to a critical value, the system undergoes a transition from conventional electrolysis to contact glow discharge electrolysis (CGDE), which has also been referred to as liquid-submerged micro-plasma, glow discharge plasma electrolysis, electrode effect, electrolytic plasma, etc. The light-emitting process is associated with the development of an irregular and erratic current time-series which has been arbitrarily labelled as "random," and thus dissuaded further research in this direction. Here, we examine the current time-series signals measured in cathodic CGDE configuration in a concentrated KOH solution at different dc bias voltages greater than the critical voltage. We show that the signals are, in fact, not random according to the NIST SP. 800-22 test suite definition. We also demonstrate that post-processing low-pass filtered sequences requires less time than the native as-measured sequences, suggesting a superposition of low frequency chaotic fluctuations and high frequency behaviors (which may be produced by more than one possible source of entropy). Using an array of nonlinear time-series analyses for dynamical systems, i.e., the computation of largest Lyapunov exponents and correlation dimensions, and re-construction of phase portraits, we found that low-pass filtered datasets undergo a transition from quasi-periodic to chaotic to quasi-hyper-chaotic behavior, and back again to chaos when the voltage controlling-parameter is increased. The high frequency part of the signals is discussed in terms of highly nonlinear turbulent motion developed around the working electrode.

  8. Characterization of Downstream Ion Energy Distributions From a High Current Hollow Cathode in a Ring Cusp Discharge Chamber

    Science.gov (United States)

    Foster, John E.; Patterson, Michael J.

    2003-01-01

    The presence of energetic ions produced by a hollow cathodes operating at high emission currents (greater than 10 Angstroms) has been documented in the literature. As part of an ongoing effort to uncover the underlying physics of the formation of these ions, ion efflux from a high current hollow cathode operating in an ion thruster discharge chamber was investigated. Using a spherical sector electrostatic energy analyzer located downstream of the discharge cathode, the ion energy distribution over a 0 to 60 eV energy range was measured. The sensitivity of the ion energy distribution function to zenith angle was also assessed at 3 different positions: 0, 15, and 25 degrees. The measurements suggest that the majority of the ion current at the measuring point falls into the analyzer with an energy approximately equal to the discharge voltage. The ion distribution, however, was found to be quite broad. The high energy tail of the distribution function tended to grow with increasing discharge current. Sensitivity of the profiles to flow rate at fixed discharge current was also investigated. A simple model is presented that provides a potential mechanism for the production of ions with energies above the discharge voltage.

  9. Determining the Limiting Current Density of Vanadium Redox Flow Batteries

    OpenAIRE

    Jen-Yu Chen; Chin-Lung Hsieh; Ning-Yih Hsu; Yi-Sin Chou; Yong-Song Chen

    2014-01-01

    All-vanadium redox flow batteries (VRFBs) are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential is affected by the electrolyte flow rate and electrolyte composition, which is related to the limiting current density. In order to investigate the effect of operating conditions on ma...

  10. Solid Oxide Electrolysis Cells: Degradation at High Current Densities

    DEFF Research Database (Denmark)

    Knibbe, Ruth; Traulsen, Marie Lund; Hauch, Anne; Ebbesen, Sune; Mogensen, Mogens Bjerg

    2010-01-01

    The degradation of Ni/yttria-stabilized zirconia (YSZ)-based solid oxide electrolysis cells operated at high current densities was studied. The degradation was examined at 850°C, at current densities of −1.0, −1.5, and −2.0 A/cm2, with a 50:50 (H2O:H2) gas supplied to the Ni/YSZ hydrogen electrode...

  11. DISCONTINUOUS FLOW OF TURBID DENSITY CURRENTS Ⅱ. INTERNAL HYDRAULIC JUMP

    Institute of Scientific and Technical Information of China (English)

    Jiahua FAN

    2005-01-01

    Traveling and stationary internal hydraulic jumps in density currents with positive or negative entrainment coefficients were analyzed based on simple assumptions. An expression of internal hydraulic jumps with entrainment coefficients was derived. Experimental data, published in literature, of stationary internal hydraulic jumps in turbid, thermal and saline density currents including measured values of water entrainment were used to compare with theory. Comparison was also made of traveling internal hydraulic jumps between measured data and theory.

  12. Effect of external magnetic field on critical current for the onset of virtual cathode oscillations in relativistic electron beams

    Science.gov (United States)

    Hramov, Alexander; Koronovskii, Alexey; Morozov, Mikhail; Mushtakov, Alexander

    2008-02-01

    In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [D.J. Sullivan, J.E. Walsh, E. Coutsias, in: V.L. Granatstein, I. Alexeff (Eds.), Virtual Cathode Oscillator (Vircator) Theory, in: High Power Microwave Sources, vol. 13, Artech House Microwave Library, 1987, Chapter 13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields.

  13. Effect of external magnetic field on critical current for the onset of virtual cathode oscillations in relativistic electron beams

    Energy Technology Data Exchange (ETDEWEB)

    Hramov, Alexander [Faculty of Nonlinear Processes, Saratov State University, Astrakhanskaya 83, Saratov 410012 (Russian Federation)], E-mail: aeh@nonlin.sgu.ru; Koronovskii, Alexey; Morozov, Mikhail; Mushtakov, Alexander [Faculty of Nonlinear Processes, Saratov State University, Astrakhanskaya 83, Saratov 410012 (Russian Federation)

    2008-02-04

    In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [D.J. Sullivan, J.E. Walsh, E. Coutsias, in: V.L. Granatstein, I. Alexeff (Eds.), Virtual Cathode Oscillator (Vircator) Theory, in: High Power Microwave Sources, vol. 13, Artech House Microwave Library, 1987, Chapter 13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields.

  14. Stored energies for electric and magnetic current densities

    CERN Document Server

    Jonsson, B L G

    2016-01-01

    Electric and magnetic current densities are an essential part of electromagnetic theory. The goal of the present paper is to define and investigate stored energies that are valid for structures that can support both electric and magnetic current densities. Stored energies normalized with the dissipated power give us the Q factor, or antenna Q, for the structure. Lower bounds of the Q factor provide information about the available bandwidth for passive antennas that can be realized in the structure. The definition that we propose is valid beyond the leading order small antenna limit. Our starting point is the energy density with subtracted far-field form which we obtain an explicit and numerically attractive current density representation. This representation gives us the insight to propose a coordinate independent stored energy. Furthermore, we find here that lower bounds on antenna Q for structures with e.g. electric dipole radiation can be formulated as convex optimization problems. We determine lower bound...

  15. Cathode erosion in a high-pressure high-current arc: calculations for tungsten cathode in a free-burning argon arc

    International Nuclear Information System (INIS)

    The motion of an evaporated atom of the cathode material in a near-cathode plasma is considered. It is shown that the evaporated atom is ionized almost instantly. The created ion, under the influence of a strong electric field existing in the cathode proximity, has a high probability of returning to the cathode. A small fraction of evaporated atoms are able to diffuse away from the cathode to the region where they are involved in plasma flow and lose their chance to return to the cathode. The fraction of the total evaporated atoms, which do not return to the cathode, the escape factor, determines the net erosion rate. In order to calculate this factor, the distributions of the plasma parameters in the near-cathode plasma were considered. Calculations showed that the escape factor is on the order of a few per cent. Using experimental data on the plasma and cathode temperatures, we calculated the net erosion rate for a free-burning 200 A argon arc with a thoriated tungsten cathode. The calculated erosion rate is close to 1 µg s-1, which is in agreement with available experimental data. (paper)

  16. Influence of the cold cathode material on the operating mode of the pulse high-current vacuum diode in a microsecond range

    International Nuclear Information System (INIS)

    The present work is aimed at the description of experimental results on the drop fraction of high-power electrical vacuum discharge and analysis of processes,which take place in cold cathodes working in microsecond range of pulses,and also on the influence of the material of a cold cathode on the operating mode of the pulse high-current vacuum diode

  17. Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

    Science.gov (United States)

    Jain, Akshay; Aravindan, Vanchiappan; Jayaraman, Sundaramurthy; Kumar, Palaniswamy Suresh; Balasubramanian, Rajasekhar; Ramakrishna, Seeram; Madhavi, Srinivasan; Srinivasan, M. P.

    2013-10-01

    In this manuscript, a dramatic increase in the energy density of ~ 69 Wh kg-1 and an extraordinary cycleability ~ 2000 cycles of the Li-ion hybrid electrochemical capacitors (Li-HEC) is achieved by employing tailored activated carbon (AC) of ~ 60% mesoporosity derived from coconut shells (CS). The AC is obtained by both physical and chemical hydrothermal carbonization activation process, and compared to the commercial AC powders (CAC) in terms of the supercapacitance performance in single electrode configuration vs. Li. The Li-HEC is fabricated with commercially available Li4Ti5O12 anode and the coconut shell derived AC as cathode in non-aqueous medium. The present research provides a new routine for the development of high energy density Li-HEC that employs a mesoporous carbonaceous electrode derived from bio-mass precursors.

  18. A high current density DC magnetohydrodynamic (MHD) micropump

    NARCIS (Netherlands)

    Homsy, Alexandra; Koster, Sander; Eijkel, Jan C.T.; Berg, van den Albert; Lucklum, F.; Verpoorte, E.; Rooij, de Nico F.

    2005-01-01

    This paper describes the working principle of a DC magnetohydrodynamic (MHD) micropump that can be operated at high DC current densities (J) in 75-µm-deep microfluidic channels without introducing gas bubbles into the pumping channel. The main design feature for current generation is a micromachined

  19. A high current density DC magnetohydrodynamic (MHD) micropump

    NARCIS (Netherlands)

    Homsy, A; Koster, Sander; Eijkel, JCT; van den Berg, A; Lucklum, F; Verpoorte, E; de Rooij, NF

    2005-01-01

    This paper describes the working principle of a DC magnetohydrodynamic (MHD) micropump that can be operated at high DC current densities (J) in 75-mu m-deep microfluidic channels without introducing gas bubbles into the pumping channel. The main design feature for current generation is a micromachin

  20. Estimation of current density distribution under electrodes for external defibrillation

    Directory of Open Access Journals (Sweden)

    Papazov Sava P

    2002-12-01

    Full Text Available Abstract Background Transthoracic defibrillation is the most common life-saving technique for the restoration of the heart rhythm of cardiac arrest victims. The procedure requires adequate application of large electrodes on the patient chest, to ensure low-resistance electrical contact. The current density distribution under the electrodes is non-uniform, leading to muscle contraction and pain, or risks of burning. The recent introduction of automatic external defibrillators and even wearable defibrillators, presents new demanding requirements for the structure of electrodes. Method and Results Using the pseudo-elliptic differential equation of Laplace type with appropriate boundary conditions and applying finite element method modeling, electrodes of various shapes and structure were studied. The non-uniformity of the current density distribution was shown to be moderately improved by adding a low resistivity layer between the metal and tissue and by a ring around the electrode perimeter. The inclusion of openings in long-term wearable electrodes additionally disturbs the current density profile. However, a number of small-size perforations may result in acceptable current density distribution. Conclusion The current density distribution non-uniformity of circular electrodes is about 30% less than that of square-shaped electrodes. The use of an interface layer of intermediate resistivity, comparable to that of the underlying tissues, and a high-resistivity perimeter ring, can further improve the distribution. The inclusion of skin aeration openings disturbs the current paths, but an appropriate selection of number and size provides a reasonable compromise.

  1. Limiting current density and water dissociation in bipolar membranes

    OpenAIRE

    Strathmann, H.; Krol, J.J.; Rapp, H.-J.; Eigenberger, G.

    1997-01-01

    The behaviour of bipolar membranes in NaCl and Na2SO4 solutions is discussed. The membranes are characterized in terms of their limiting current densities. Below the limiting current density the electric current is carried by salt ions migrating from the transition region between the anion and the cation exchange layer of the bipolar membrane. In steady state these ions are replaced by salt ions transported from the bulk solutions into the transition region by diffusion and migration due to t...

  2. Casimir effect for scalar current densities in topologically nontrivial spaces

    Energy Technology Data Exchange (ETDEWEB)

    Bellucci, S. [INFN, Laboratori Nazionali di Frascati, Frascati (Italy); Saharian, A.A.; Saharyan, N.A. [Yerevan State University, Department of Physics, Yerevan (Armenia)

    2015-08-15

    We evaluate the Hadamard function and the vacuum expectation value (VEV) of the current density for a charged scalar field, induced by flat boundaries in spacetimes with an arbitrary number of toroidally compactified spatial dimensions. The field operator obeys the Robin conditions on the boundaries and quasiperiodicity conditions with general phases along compact dimensions. In addition, the presence of a constant gauge field is assumed. The latter induces Aharonov-Bohm-type effect on the VEVs. There is a region in the space of the parameters in Robin boundary conditions where the vacuum state becomes unstable. The stability condition depends on the lengths of compact dimensions and is less restrictive than that for background with trivial topology. The vacuum current density is a periodic function of the magnetic flux, enclosed by compact dimensions, with the period equal to the flux quantum. It is explicitly decomposed into the boundary-free and boundary-induced contributions. In sharp contrast to the VEVs of the field squared and the energy-momentum tensor, the current density does not contain surface divergences. Moreover, for Dirichlet condition it vanishes on the boundaries. The normal derivative of the current density on the boundaries vanish for both Dirichlet and Neumann conditions and is nonzero for general Robin conditions. When the separation between the plates is smaller than other length scales, the behavior of the current density is essentially different for non-Neumann and Neumann boundary conditions. In the former case, the total current density in the region between the plates tends to zero. For Neumann boundary condition on both plates, the current density is dominated by the interference part and is inversely proportional to the separation. (orig.)

  3. Effect of LiFePO4 cathode density and thickness on electrochemical performance of lithium metal polymer batteries prepared by in situ thermal polymerization

    International Nuclear Information System (INIS)

    Highlights: • Electrode density and thickness affect redox property of lithium metal polymer cells. • Higher density and lower thickness in LiFePO4 cathodes lead to better performances. • An optimized LiFePO4 and polymer electrolyte delivers a good cycle life at a 2 C rate. - Abstract: In order to investigate the effects of electrode density and thickness on the room temperature electrochemical performance of lithium metal polymer batteries (LMPBs), four LiFePO4 cathodes with different electrode density/thickness (1.6 g cm−3/20 μm, 1.6 g cm−3/40 μm, 2.0 g cm−3/20 μm, and 2.0 g cm−3/40 μm) are prepared. Several types of unit cells employing each cathode are prepared using in situ thermally cross-linked polymer electrolytes controlled under the same manufacturing condition. The unit cells employing the thinnest cathode with highest density achieve the most improved rate capability and cycle life, which seems to be attributed to the higher electrical conductivity of the cathode and shorter diffusion length of Li+ ions within the cathode pores. In addition, the LMPB with an optimized LiFePO4 cathode (2.0 g cm−3, 20 μm) and polymer electrolyte (5 vol% of the crosslinking agent with non-volatile liquid electrolytes) delivers a high and stable charge/discharge capacity under very fast charging and discharging conditions (at a 2 C rate) at room temperature

  4. Dynamics of a relativistic electron beam in a high-current diode with a knife-edge cathode

    International Nuclear Information System (INIS)

    For a number of practical applications, e.g., producing discharges in large volumes in order to pump gas lasers and for short x-ray pulses, it is necessary to generate electron beams in megamp range with electron energies from hundreds of kilovolts to several megavolts. It has been possible to obtain high currents (I ± 1 MA) by using diodes with knife-edge cathodes. Knife-edge diodes have an important advantage over the parapotential type because the ion current in them comprises a relatively small fraction of the total current. This is because the electron path in the accelerating gap of knife-edge diodes is quite short in comparison with that in high-current parapotential diodes. From the point of view of applying ribbon-shaped or narrow electron beams, the important problems are in measuring the current-voltage characteristics of the diodes and determining the dynamics of the energy spectrum and the angular spread of the electrons. The generation of an electron beam with a current ∼130 kA and pulse length ∼60 ns is studied. The current-voltage characteristics of knife-edge diodes with various geometries, the dynamics of the angular spread, and the beam structure are studied. As a result of the study of the REB dynamics it is found that the operation of the diode with these experiments can be approximated by a proposed formula which includes the finite thickness of the knife-edge cathode and the motion of the plasma and ions in the discharge gap. Breaking up of the beam into individual current-carrying channels is observed with the characteristic scale ∼1-2 mm. It is noted that for the diode geometry with a knife-edge cathode, when the magnetic field changes sign and passes through zero, an instability can exist which is analogous to the dissipative tearing instability

  5. Dispersal and air entrainment in unconfined dilute pyroclastic density currents

    Science.gov (United States)

    Andrews, Benjamin J.

    2014-09-01

    Unconfined scaled laboratory experiments show that 3D structures control the behavior of dilute pyroclastic density currents (PDCs) during and after liftoff. Experiments comprise heated and ambient temperature 20 μm talc powder turbulently suspended in air to form density currents within an unobstructed 8.5 × 6 × 2.6-m chamber. Comparisons of Richardson, thermal Richardson, Froude, Stokes, and settling numbers and buoyant thermal to kinetic energy densities show good agreement between experimental currents and dilute PDCs. The experimental Reynolds numbers are lower than those of PDCs, but the experiments are fully turbulent; thus, the large-scale dynamics are similar between the two systems. High-frequency, simultaneous observation in three orthogonal planes shows that the currents behave very differently than previous 2D (i.e., confined) currents. Specifically, whereas ambient temperature currents show radial dispersal patterns, buoyancy reversal, and liftoff of heated currents focuses dispersal along narrow axes beneath the rising plumes. The aspect ratios, defined as the current length divided by a characteristic width, are typically 2.5-3.5 in heated currents and 1.5-2.5 in ambient temperature currents, reflecting differences in dispersal between the two types of currents. Mechanisms of air entrainment differ greatly between the two currents: entrainment occurs primarily behind the heads and through the upper margins of ambient temperature currents, but heated currents entrain air through their lateral margins. That lateral entrainment is much more efficient than the vertical entrainment, >0.5 compared to ˜0.1, where entrainment is defined as the ratio of cross-stream to streamwise velocity. These experiments suggest that generation of coignimbrite plumes should focus PDCs along narrow transport axes, resulting in elongate rather than radial deposits.

  6. Assessment of anodal and cathodal transcranial direct current stimulation (tDCS) on MMN-indexed auditory sensory processing.

    Science.gov (United States)

    Impey, Danielle; de la Salle, Sara; Knott, Verner

    2016-06-01

    Transcranial direct current stimulation (tDCS) is a non-invasive form of brain stimulation which uses a very weak constant current to temporarily excite (anodal stimulation) or inhibit (cathodal stimulation) activity in the brain area of interest via small electrodes placed on the scalp. Currently, tDCS of the frontal cortex is being used as a tool to investigate cognition in healthy controls and to improve symptoms in neurological and psychiatric patients. tDCS has been found to facilitate cognitive performance on measures of attention, memory, and frontal-executive functions. Recently, a short session of anodal tDCS over the temporal lobe has been shown to increase auditory sensory processing as indexed by the Mismatch Negativity (MMN) event-related potential (ERP). This preliminary pilot study examined the separate and interacting effects of both anodal and cathodal tDCS on MMN-indexed auditory pitch discrimination. In a randomized, double blind design, the MMN was assessed before (baseline) and after tDCS (2mA, 20min) in 2 separate sessions, one involving 'sham' stimulation (the device is turned off), followed by anodal stimulation (to temporarily excite cortical activity locally), and one involving cathodal stimulation (to temporarily decrease cortical activity locally), followed by anodal stimulation. Results demonstrated that anodal tDCS over the temporal cortex increased MMN-indexed auditory detection of pitch deviance, and while cathodal tDCS decreased auditory discrimination in baseline-stratified groups, subsequent anodal stimulation did not significantly alter MMN amplitudes. These findings strengthen the position that tDCS effects on cognition extend to the neural processing of sensory input and raise the possibility that this neuromodulatory technique may be useful for investigating sensory processing deficits in clinical populations. PMID:27054908

  7. A series of tufted carbon fiber cathodes designed for different high power microwave sources

    Science.gov (United States)

    Liu, Lie; Li, Limin; Zhang, Jun; Zhang, Xiaoping; Wen, Jianchun; Liu, Yonggui

    2008-06-01

    We report the fabrication technique of tufted carbon fiber cathodes for different microwave sources. Three carbon fiber cathodes were constructed, including a planar cathode, an annular cathode, and a cylindrical cathode for radial emission. Experimental investigations on these cathodes were performed in a reflex triode virtual cathode oscillator (vircator), a backward wave oscillator (BWO), and a magnetically insulated transmission line oscillator (MILO), respectively. The pulse duration of microwave emission from the reflex triode vircator was lengthened by using the planar carbon fiber cathode. In the BWO with the annular carbon fiber cathode, the uniform electron beam with a kA /cm2 current density was observed. In addition, carbon fiber has great promise as field emitter for MILOs. These results show that the carbon fiber cathodes can be utilized for electron emission in high power diodes with different structures.

  8. Current drive at plasma densities required for thermonuclear reactors.

    Science.gov (United States)

    Cesario, R; Amicucci, L; Cardinali, A; Castaldo, C; Marinucci, M; Panaccione, L; Santini, F; Tudisco, O; Apicella, M L; Calabrò, G; Cianfarani, C; Frigione, D; Galli, A; Mazzitelli, G; Mazzotta, C; Pericoli, V; Schettini, G; Tuccillo, A A

    2010-01-01

    Progress in thermonuclear fusion energy research based on deuterium plasmas magnetically confined in toroidal tokamak devices requires the development of efficient current drive methods. Previous experiments have shown that plasma current can be driven effectively by externally launched radio frequency power coupled to lower hybrid plasma waves. However, at the high plasma densities required for fusion power plants, the coupled radio frequency power does not penetrate into the plasma core, possibly because of strong wave interactions with the plasma edge. Here we show experiments performed on FTU (Frascati Tokamak Upgrade) based on theoretical predictions that nonlinear interactions diminish when the peripheral plasma electron temperature is high, allowing significant wave penetration at high density. The results show that the coupled radio frequency power can penetrate into high-density plasmas due to weaker plasma edge effects, thus extending the effective range of lower hybrid current drive towards the domain relevant for fusion reactors. PMID:20975718

  9. Scaling rules for critical current density in anisotropic biaxial superconductors

    Science.gov (United States)

    Li, Yingxu; Kang, Guozheng; Gao, Yuanwen

    2016-06-01

    Recent researches highlight the additional anisotropic crystallographic axis within the superconducting plane of high temperature superconductors (HTS), demonstrating the superconducting anisotropy of HTS is better understood in the biaxial frame than the previous uniaxial coordinates within the superconducting layer. To quantitatively evaluate the anisotropy of flux pinning and critical current density in HTS, we extend the scaling rule for single-vortex collective pinning in uniaxial superconductors to account for flux-bundle collective pinning in biaxial superconductors. The scaling results show that in a system of random uncorrected point defects, the field dependence of the critical current density is described by a unified function with the scaled magnetic field of the isotropic superconductor. The obtained angular dependence of the critical current density depicts the main features of experimental observations, considering possible corrections due to the strong-pinning interaction.

  10. Engineering Critical Current Density Improvement in Ag- Bi-2223 Tapes

    DEFF Research Database (Denmark)

    Wang, W. G.; Seifi, Behrouz; Eriksen, Morten; Skov-Hansen, Peder; Grivel, J. -C.; Vase, Per

    Ag alloy sheathed Bi-2223 multifilament tapes were produced by the powder-in-tube method. Engineering critical current density improvement has been achieved through both enhancement of critical current density by control of the thermal behavior of oxide powder and by an increase of the filling...... superconductor composite sustaining large proportional oxide ceramics in the composite during drawing and rolling process. By optimization of the thermal and mechanical process, a Je of 12 kA/cm2 has been achieved in a 0.183.1 mm2 size tape which carried 67 A...

  11. Three-dimensional structure of dilute pyroclastic density currents

    Science.gov (United States)

    Andrews, B. J.

    2013-12-01

    Unconfined experimental density currents dynamically similar to pyroclastic density currents (PDCs) suggest that cross-stream motions of the currents and air entrainment through currents' lateral margins strongly affects PDC behavior. Experiments are conducted within an air-filled tank 8.5 m long by 6.1 m wide by 2.6 m tall. Currents are generated by feeding heated powders down a chute into the tank at controlled rates to form dilute, particle-laden, turbulent gravity currents that are fed for 30 to 600 seconds. Powders include 5 μm aluminum oxide, 25 μm talc, 27 μm walnut, 76 μm glass beads and mixtures thereof. Experiments are scaled such that Froude, densimetric and thermal Richardson, particle Stokes and Settling numbers, and thermal to kinetic energy densities are all in agreement with dilute PDCs; experiments have lower Reynolds numbers that natural currents, but the experiments are fully turbulent, thus the large scale structures should be similar. The experiments are illuminated with 3 orthogonal laser sheets (650, 532, and 450 nm wavelengths) and recorded with an array of HD video cameras and a high speed camera (up to 3000 fps); this system provides synchronous observation of a vertical streamwise and cross-stream planes, and a horizontal plane. Ambient temperature currents tend to spread out radially from the source and have long run out distances, whereas warmer currents tend to focus along narrow sectors and have shorter run outs. In addition, when warm currents lift off to form buoyant plumes, lateral spreading ceases. The behavior of short duration currents are dominated by the current head; as eruption duration increases, current transport direction tends to oscillate back and forth (this is particularly true for ambient temperature currents). Turbulent structures in the horizontal plane show air entrainment and advection downstream. Eddies illuminated by the vertical cross-stream laser sheet often show vigorous mixing along the current margins

  12. Current Density Imaging through Acoustically Encoded Magnetometry: A Theoretical Exploration

    CERN Document Server

    Sheltraw, Daniel J

    2014-01-01

    The problem of determining a current density confined to a volume from measurements of the magnetic field it produces exterior to that volume is known to have non-unique solutions. To uniquely determine the current density, or the non-silent components of it, additional spatial encoding of the electric current is needed. In biological systems such as the brain and heart, which generate electric current associated with normal function, a reliable means of generating such additional encoding, on a spatial and temporal scale meaningful to the study of such systems, would be a boon for research. This paper explores a speculative method by which the required additional encoding might be accomplished, on the time scale associated with the propagation of sound across the volume of interest, by means of the application of a radially encoding pulsed acoustic spherical wave.

  13. Power generation using an activated carbon and metal mesh cathode in a microbial fuel cell

    KAUST Repository

    Zhang, Fang

    2009-11-01

    An inexpensive activated carbon (AC) air cathode was developed as an alternative to a platinum-catalyzed electrode for oxygen reduction in a microbial fuel cell (MFC). AC was cold-pressed with a polytetrafluoroethylene (PTFE) binder to form the cathode around a Ni mesh current collector. This cathode construction avoided the need for carbon cloth or a metal catalyst, and produced a cathode with high activity for oxygen reduction at typical MFC current densities. Tests with the AC cathode produced a maximum power density of 1220 mW/m2 (normalized to cathode projected surface area; 36 W/m3 based on liquid volume) compared to 1060 mW/m2 obtained by Pt catalyzed carbon cloth cathode. The Coulombic efficiency ranged from 15% to 55%. These findings show that AC is a cost-effective material for achieving useful rates of oxygen reduction in air cathode MFCs. © 2009 Elsevier B.V. All rights reserved.

  14. Analisa Teknis dan Ekonomis Penggunaan ICCP (Impressed Current Cathodic Protection Dibandingkan dengan Sacrificial Anode dalam Proses Pencegahan Korosi

    Directory of Open Access Journals (Sweden)

    Afif Wiludin

    2013-03-01

    Full Text Available Perlindungan badan kapal  terhadap korosi dengan  menggunakan  metode perlindungan katodik pada prinsipnya adalah sel elektrokimia untuk mengendalikan korosi dengan mengkonsentrasikan reaksi oksigen pada sel galvanik dan menekan korosi pada katoda dalam sel yang sama. Pada proteksi katodik, logam yang akan dilindungi dijadikan katoda dan reaksi oksidasi terjadi di anoda. Ada dua macam cathodic protection yaitu Sacrificial Anode Cathodic Protection (SACP dan Impressed Current Cathodic Protection (ICCP. Dilakukan penelitian tentang analisa teknis dan ekonomis penggunaan ICCP dibandingkan dengan SACP dalam proses pencegahan korosi, kedua sistem dibandingkan dalam jangka 20 tahun, dari segi teknis dengan menggunakan perbandingan perhitungan sesuai standar DnV, yang dibandingkan dari tahap design, tahap instalasi, dan maintenance, dari segi ekonomis perbandingan dibedakan dari tahap pengadaan komponen-komponen sistem, tahap instalasi, dan tahap maintenance. Data perbandingan diperoleh dengan perhitungan sesuai standar, study literature, diskusi dan interview. Hasil perhitungan perbandingan yang diperkirakan selama 20 tahun, dari segi teknis kedua sistem memenuhi standar yang berdasar pada sistem perhitungan standar DnV B-401, sedangkan dari segi ekonomis, biaya untuk sistem ICCP sebesar Rp. 205.405.000,00 dan sistem SACP sebesar Rp. 562.590.000,00, sehingga lebih ekonomis menggunakan sistem ICCP sebesar Rp 357.185.000, 00 atau 63,49% dari biaya untuk sistem SACP

  15. Using Multispectral Imaging to Measure Temperature Profiles and Emissivity of Large Thermionic Dispenser, Cathodes

    International Nuclear Information System (INIS)

    Thermionic dispenser cathodes are widely used in modern high-power microwave tubes. Use of these cathodes has led to significant improvement in performance. In recent years these cathodes have been used in electron linear accelerators (LINACs), particularly in induction LINACs, such as the Experimental Test Accelerator at Lawrence Livermore National Laboratory and the Relativistic Test Accelerator at Lawrence Berkeley National Laboratory. For induction LINACs, the thermionic dispenser cathode provides greater reproducibility, longer pulse lengths, and lower emittance beams than does a field emission cathode. Los Alamos National Laboratory is fabricating a dual-axis X-ray radiography machine called dual-axis radiograph hydrodynamic test (DARHT). The second axis of DARHT consists of a 2-kA, 20-MeV induction LINAC that uses a 3.2-MeV electron gun with a tungsten thermionic-dispenser cathode. Typically the DARHT cathode current density is 10 A/cm2 at 1050 C. Under these conditions current density is space-charge limited, which is desirable since current density is independent of temperature. At lower temperature (the temperature-limited regime) there are variations in the local current density due to a nonuniform temperature profile. To obtain the desired uniform current density associated with space-charge limited operation, the coolest area on the cathode must be at a sufficiently high temperature so that the emission is space-charge limited. Consequently, the rest of the cathode is emitting at the same space-charge-limited current density but is at a higher temperature than necessary. Because cathode lifetime is such a strong function of cathode temperature, there is a severe penalty for nonuniformity in the cathode temperature. For example, a temperature increase of 50 C means cathode lifetime will decrease by a factor of at least four. Therefore, we are motivated to measure the temperature profiles of our large-area cathodes

  16. Direct current-induced electrogenerated chemiluminescence of hydrated and chelated Tb(III) at aluminum cathodes

    International Nuclear Information System (INIS)

    Cathodic DC polarization of oxide-covered aluminum produces electrogenerated chemiluminescence from hydrated and chelated Tb(III) ions in aqueous electrolyte solutions. At the moment of cathodic voltage onset, a strong cathodic flash is observed, which is attributed to a tunnel emission of hot electrons into the aqueous electrolyte solution and the successive chemical reactions with the luminophores. However, within a few milliseconds the insulating oxide film is damaged and finally dissolved due to (i) indiffusion of protons or alkali metal ions into the thin oxide film, (ii) subsequent hydrogen evolution at the aluminum/oxide interface and (iii) alkalization of the electrode surface induced by hydrogen evolution reaction. When the alkalization of the electrode surface has proceeded sufficiently, chemiluminescence is generated with increasing intensity. Aluminum metal, short-lived Al(II), Al(I) or atomic hydrogen and its conjugated base form, hydrated electron, can act as highly reducing species in addition to the less energetic heterogeneously transferred electrons from the aluminum electrode. Tb(III) added as a hydrated ion in the solution probably luminesces in the form of Tb(OH)3 or Tb(OH)4- by direct redox reactions of the central ion whereas multidentate aromatic ligand chelated Tb(III) probably luminesces by ligand sensitized chemiluminescence mechanism in which ligand is first excited by one-electron redox reactions, which is followed by intramolecular energy transfer to the central ion which finally emits light

  17. Density currents as a desert dust mobilization mechanism

    Directory of Open Access Journals (Sweden)

    S. Solomos

    2012-08-01

    Full Text Available The formation and propagation of density currents are well studied processes in fluid dynamics with many applications to other science fields. In the atmosphere, density currents are usually meso-β/γ mechanisms and are often associated with storm downdrafts. These storms are responsible for the formation of severe dust episodes (haboobs over desert areas. In the present study, the formation of a convective cool pool and the associated dust mobilization is examined for a representative event over the western part of Sahara desert. The physical processes involved in the mobilization of dust are described in the framework of the integrated atmospheric-air quality RAMS/ICLAMS model. Dust is effectively produced due to the development of near surface vortices and increased turbulence mixing along the frontal line. Increased dust emissions and recirculation of the elevated particles inside the density current head result in the formation of a moving "dust wall". Transport of the uplifted dust in higher layers – outside of the density current – occurs mainly in three ways: (1 uplifting of preexisting dust over the frontal line with the aid of the strong updraft (2 entrainment at the upper part of the density current head due to turbulent mixing (3 vertical mixing after the dilution of the system. The role of the produced dust in the associated convective cloud system was found to be limited. Proper representation of convective processes and dust fluxes requires the use of high resolution (cloud resolving model configuration and online parameterization of dust production. Haboob-type of dust storms are effective dust sources and should be treated accordingly in dust modeling applications.

  18. Density currents as a desert dust mobilization mechanism

    Directory of Open Access Journals (Sweden)

    S. Solomos

    2012-11-01

    Full Text Available The formation and propagation of density currents are well studied processes in fluid dynamics with many applications in other science fields. In the atmosphere, density currents are usually meso-β/γ phenomena and are often associated with storm downdrafts. These storms are responsible for the formation of severe dust episodes (haboobs over desert areas. In the present study, the formation of a convective cool pool and the associated dust mobilization are examined for a representative event over the western part of Sahara desert. The physical processes involved in the mobilization of dust are described with the use of the integrated atmospheric-air quality RAMS/ICLAMS model. Dust is effectively produced due to the development of near surface vortices and increased turbulent mixing along the frontal line. Increased dust emissions and recirculation of the elevated particles inside the head of the density current result in the formation of a moving "dust wall". Transport of the dust particles in higher layers – outside of the density current – occurs mainly in three ways: (1 Uplifting of preexisting dust over the frontal line with the aid of the strong updraft (2 Entrainment at the upper part of the density current head due to turbulent mixing (3 Vertical mixing after the dilution of the system. The role of the dust in the associated convective cloud system was found to be limited. Proper representation of convective processes and dust mobilization requires the use of high resolution (cloud resolving model configuration and online parameterization of dust production. Haboob-type dust storms are effective dust sources and should be treated accordingly in dust modeling applications.

  19. Ionospheric midlatitude electric current density inferred from multiple magnetic satellites

    DEFF Research Database (Denmark)

    Shore, R. M.; Whaler, K. A.; Macmillan, S.;

    2013-01-01

    . Zonal current density from sources in only the region between the two satellites is estimated for the first time. Six years of mutually available vector magnetic data allows overlaps spanning the full 24 h range of local time twice. Solutions are computed on an event-by-event basis after correcting......A method for inferring zonal electric current density in the mid-to-low latitude F region ionosphere is presented. We describe a method of using near-simultaneous overflights of the Ørsted and CHAMP satellites to define a closed circuit for an application of Ampère's integral law to magnetic data...... for estimates of main and crustal magnetic fields. Current density in the range ±0.1 μA/m2 is resolved, with the distribution of electric current largely matching known features such as the Appleton anomaly. The currents appear unmodulated at times of either high-negative Dst or high F10.7, which has...

  20. The density matrix picture of laser coherent control current

    Institute of Scientific and Technical Information of China (English)

    SHOU Qian; ZHANG Haichao; LIU Luning; LIN Weizhu

    2004-01-01

    The physical substance of the coherent control current and the optical rectification have been analyzed based on density matrix perturbation theory. The analytical results demonstrate that they arise from the real and virtual manifestations of the same nonlinear process associated with diagonal and non-diagonal density matrix.And in terms of polarization, they respectively arise from the intraband and interband polarizations. Both the evolution of the coherent control current exited by ultrafast laser pulse and its dependence on frequency have been studied in time and frequency domains. In order to get an explicit knowledge of intraband polarization and the origination of the coherent control current, we have investigated the initial photo-carriers momentum distribution. The ultrafast decay of the polar momentum population in order of tens of femtosends is given to illustrate its instantaneous optical response.

  1. Transport studies in polymer electrolyte fuel cell with porous metallic flow field at ultra high current density

    Science.gov (United States)

    Srouji, Abdul-Kader

    Achieving cost reduction for polymer electrolyte fuel cells (PEFC) requires a simultaneous effort in increasing power density while reducing precious metal loading. In PEFCs, the cathode performance is often limiting due to both the slow oxygen reduction reaction (ORR), and mass transport limitation caused by limited oxygen diffusion and liquid water flooding at high current density. This study is motivated by the achievement of ultra-high current density through the elimination of the channel/land (C/L) paradigm in PEFC flow field design. An open metallic element (OME) flow field capable of operating at unprecedented ultra-high current density (3 A/cm2) introduces new advantages and limitations for PEFC operation. The first part of this study compares the OME with a conventional C/L flow field, through performance and electrochemical diagnostic tools such as electrochemical impedance spectroscopy (EIS). The results indicate the uniqueness of the OME's mass transport improvement. No sign of operation limitation due to flooding is noted. The second part specifically examines water management at high current density using the OME flow field. A unique experimental setup is developed to measure steady-state and transient net water drag across the membrane, in order to characterize the fundamental aspects of water transport at high current density with the OME. Instead of flooding, the new limitation is identified to be anode side dry-out of the membrane, caused by electroosmotic drag. The OME improves water removal from the cathode, which immediately improves oxygen transport and performance. However, the low water content in the cathode reduces back diffusion of water to the membrane, and electroosmotic drag dominates at high current density, leading to dry-out. The third part employs the OME flow field as a tool that avoids C/L effects endemic to a typical flow field, in order to study oxygen transport resistance at the catalyst layer of a PEFC. In open literature, a

  2. Transport and sedimentation in unconfined experimental dilute pyroclastic density currents

    Science.gov (United States)

    Ramirez, G.; Andrews, B. J.; Dennen, R. L.

    2013-12-01

    We present results from experiments conducted in a new facility that permits the study of large, unconfined particle laden density currents that are dynamically similar to natural dilute pyroclastic density currents (PDCs). Experiments were run in a sealed, air-filled tank measuring 8.5 m long by 6.1 m wide by 2.6 m tall. Currents were generated by feeding mixture of heated particles (5 μm aluminum oxide, 25 μm talc, 27 μm walnut shell, 76 μm glass beads) down a chute at controlled rates to produce dilute, turbulent gravity currents. Comparison of experimental currents with natural PDCs shows good agreement between Froude, densimetric and thermal Richardson, and particle Stokes and settling numbers; experimental currents have lower Reynolds numbers than natural PDCs, but are fully turbulent. Currents were illuminated with 3 orthogonal laser sheets (650, 532, and 450 nm wavelengths) and recorded with an array of HD video cameras and a high speed camera (up to 3000 fps). Deposits were mapped using a grid of sedimentation traps. We observe distinct differences between ambient temperature and warm currents: * warm currents have shorter run out distances, narrow map view distributions of currents and deposits, thicken with distance from the source, and lift off to form coignimbrite plumes; * ambient temperature currents typically travel farther, spread out radially, do not thicken greatly with transport distance, and do not form coignimbrite plumes. Long duration currents (600 s compared to 30-100 s) oscillate laterally with time (e.g. transport to the right, then the left, and back); this oscillation happens prior to any interaction with the tank walls. Isopach maps of the deposits show predictable trends in sedimentation versus distance in response to eruption parameters (eruption rate, duration, temperature, and initial current mass), but all sedimentation curves can be fit with 2nd order polynomials (R2>.9). Proximal sedimentation is similar in comparable warm

  3. Large-eddy simulation of density currents on inclined beds

    Science.gov (United States)

    Chawdhary, Saurabh; Khosronejad, Ali; Christodoulou, George; Sotiropoulos, Fotis

    2013-11-01

    Density currents are stratified flow in presence of density differential and gravity field. We carry out Large-Eddy Simulation (LES) to simulate the flow of a density current formed over sloped bed due to an incoming jet of heavy density salty water for two different cases of bed slope: (a) 5 degrees and (b) 15 degrees. The Reynolds and Richardson numbers based on inlet height and inlet velocity were (a) 1100 and 0.471, and (b) 2000 and 0.0355, respectively. The Schmidt number is set equal to 620, which corresponds to the value for salt-water. The computed results are compared with laboratory experiments in terms of overall shape of the heavy-density plume and its spreading rate and are shown to be in reasonable agreement. The instantaneous LES flow fields are further analyzed to gain novel insights into the rich dynamics of coherent vortical structures in the flow. The half-width of the plume is plotted as a function of downstream length and found to exhibit three different regions on a log scale, in agreement with previous experimental findings. We acknowledge computational support from the Minnesota Supercomputing Institute.

  4. Determination of atomic and molecular particle densities and temperatures in a low-pressure hydrogen hollow cathode discharge

    International Nuclear Information System (INIS)

    Atomic (H) and molecular (H2) hydrogen densities and temperatures have been determined in a magnetized hollow cathode arc plasma burning at low pressure (p = 4-40 Pa). Rayleigh scattering measurements are used to derive the sum of atomic and molecular densities, each weighted with its scattering cross section. Coherent anti-Stokes Raman scattering (CARS) has been used to determine the population density differences of rovibrational molecular H2 states nH2 υ, J) - nH2 (υ + 1, J). The CARS intensity of many rotational states (J ≤ 9) of H2 can be detected and these levels are found to be populated according to a Boltzmann distribution. In the low-pressure plasma only the fundamental vibrational band of H2 can be found experimentally owing to the low particle densities. In order to evaluate the H2 density properly from the measured CARS data, the H2 vibrational population for υ > 0 is calculated from a spatially one-dimensional diffusion reaction model. Within the plasma centre the dissociation degree d nH/(nH2 ∼ 0.4 and about one third of the molecular hydrogen is found in vibrationally excited states. Here, the vibrational temperature is about Tvib ∼ 5000 K, which fas exceeds the gas temperature of Tgas ∼ 1000-3000 K. The dissociation degree and the vibrational distribution are mainly determined by electron-impact processes in the inner plasma region and recycling processes at the vessel walls, whereas the influence of inelastic neutral-neutral collisions is rather marginal. (author)

  5. High dislocation density of tin induced by electric current

    Energy Technology Data Exchange (ETDEWEB)

    Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung, E-mail: matkllin@mail.ncku.edu.tw [Department of Material Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan, R. O. C (China); Wu, Albert T. [Department of Chemical and Material Engineering, National Central University, Jhongli 32001, Taiwan, R. O. C (China)

    2015-12-15

    A dislocation density of as high as 10{sup 17} /m{sup 2} in a tin strip, as revealed by high resolution transmission electron microscope, was induced by current stressing at 6.5 x 10{sup 3} A/ cm{sup 2}. The dislocations exist in terms of dislocation line, dislocation loop, and dislocation aggregates. Electron Backscattered Diffraction images reflect that the high dislocation density induced the formation of low deflection angle subgrains, high deflection angle Widmanstätten grains, and recrystallization. The recrystallization gave rise to grain refining.

  6. High current density magnets for INTOR and TIBER

    International Nuclear Information System (INIS)

    The adoption of high current density, high field, superconducting magnets for INTOR and TIBER would prove beneficial. When combined with improved radiation tolerance of the magnets to minimize the inner leg shielding, a substantial reduction in machine dimensions and capital costs can be achieved. Fortunately, cable-in-conduit conductors (CICC) which are capable of the desired enhancements are being developed. Because conductor stability in a CICC depends more on the trapped helium enthalpy, rather than the copper resistivity, higher current densities of the order of 40 A/mm2 at 12 T are possible. Radiation damage to the copper stabilizer is less important because the growth in resistance is a second-order effect on stability. Such CICC conductors lend themselves naturally to niobium-tin utilization, with the benefits of the high current-sharing temperature of this material being taken to advantage in absorbing radiation heating. When the helium coolant is injected at near the critical pressure, Joule-Thompson expansion in the flow path tends to stabilize the fluid temperature at under 6 K. Thus, higher fields, as well as higher current densities, can be considered for INTOR or TIBER

  7. Hollow cathode ion source without magnetic field

    International Nuclear Information System (INIS)

    On the base of the IBM-4 ion source a hollow cathode source operating in the continuous regime is developed. The gas discharge chamber diameter equals 100 mm, chamber height - 50 mm. A hollow cathode represents a molybdenum tube with an internal diameter 13 mm and wall thickness 0,7-0,8 mm. An emitter is manufactured from zirconium carbide and lanthanum hexaboride. The investigations of the source operation have shown both cathodes operated efficiency. Electron emission density consitutes 25 A/cm2. At the 50 A discharge current ion current density in a center of plasma emitter constitutes 120 mA/cm2. As a result of the investigations carried out the compatibility of the hollow cathode and the IBM-type source is shown

  8. Effect of the energy transfer collision between noble gas and sputtered metal atom on the voltage-current curve of a hollow-cathode discharge

    International Nuclear Information System (INIS)

    The voltage-current curves and the optogalvanic signals of hollow-cathode discharge tubes were measured. Attention was focused on the existence of negative dynamic resistance properties for argon and neon discharges. Three hollow-cathodes, each was made of gadolinium, uranium, and copper, were used with both the noble gases. The negative dynamic resistance regions were observed only in Ar/U, Ar/Gd, and Ne/Cu discharges. These results suggest that resonant Penning ionization is one of the main reactions producing the negative dynamic resistance characteristics in hollow cathode discharges

  9. Ion current to a substrate in the pulsed dc hollow cathode plasma jet deposition system

    Czech Academy of Sciences Publication Activity Database

    Virostko, Petr; Hubička, Zdeněk; Čada, Martin; Tichý, M.

    2010-01-01

    Roč. 43, č. 12 (2010), s. 1-7. ISSN 0022-3727 R&D Projects: GA AV ČR KAN301370701; GA ČR GP202/09/P159; GA ČR GA202/09/0800 Grant ostatní: AVČR(CZ) M100100915 Institutional research plan: CEZ:AV0Z10100522 Keywords : plasma * pulsed DC * ion flux * hollow cathode Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.105, year: 2010 http://stacks.iop.org/JPhysD/43/124019

  10. Casimir effect for scalar current densities in topologically nontrivial spaces

    CERN Document Server

    Bellucci, S; Saharyan, N A

    2015-01-01

    We evaluate the Hadamard function and the vacuum expectation value (VEV) of the current density for a charged scalar field, induced by flat boundaries in spacetimes with an arbitrary number of toroidally compactified spatial dimensions. The field operator obeys the Robin conditions on the boundaries and quasiperiodicity conditions with general phases along compact dimensions. In addition, the presence of a constant gauge field is assumed. The latter induces Aharonov-Bohm-type effect on the VEVs. There is a region in the space of the parameters in Robin boundary conditions where the vacuum state becomes unstable. The stability condition depends on the lengths of compact dimensions and is less restrictive than that for background with trivial topology. The vacuum current density is a periodic function of the magnetic flux, enclosed by compact dimensions, with the period equal to the flux quantum. It is explicitly decomposed into the boundary-free and boundary-induced contributions. In sharp contrast to the VEVs...

  11. Vortex edge barriers and critical current density in granular superconductors

    CERN Document Server

    Belevtsov, L V

    2003-01-01

    Type-II superconductors, even without bulk pinning and in the absence of a macroscopic Bean-Livingston surface barrier for vortex penetration, can exhibit barriers for flux penetration. We investigated some new edge barriers based on the laminar model, that are governed by the anisotropy ratio, grain coupling strength, and grain size. Expressions describing the pinning potential U sub p and critical current density J sub c are derived for magnetic fields near H sub c sub 1. It is shown that edge barrier effects play a substantial role in a realistic description of the critical current density for both MgB sub 2 and high-T sub c superconductors. (Abstract Copyright [2003], Wiley Periodicals, Inc.)

  12. Aperture Size Effect on Extracted Negative Ion Current Density

    Science.gov (United States)

    de Esch, H. P. L.; Svensson, L.; Riz, D.

    2009-03-01

    This paper discusses experimental results obtained at the 1 MV testbed at CEA Cadarache that appear to show a higher extracted D- current density from small apertures. Plasma grids with different shapes have been installed and tested. All grids had one single aperture. The tests were done in volume operation and in caesium operation. We tested four grids, two with O/14 mm, one with O/11 mm and one with O/8 mm apertures. No aperture size effect was observed in volume operation. In caesiated operation the extracted current density for the O/8 mm aperture appears to be significantly higher (˜50%) than for the O/14 mm aperture. Simulations with a 3D Monte Carlo Trajectory Following Code have shown an aperture size effect of about 20%. Finally, as byproducts of the experiments, data on backstreaming positive ions and the temperature of the plasma grid have been obtained.

  13. Numerical Simulation of Density Current Evolution in a Diverging Channel

    Directory of Open Access Journals (Sweden)

    Mitra Javan

    2012-01-01

    Full Text Available When a buoyant inflow of higher density enters a reservoir, it sinks below the ambient water and forms an underflow. Downstream of the plunge point, the flow becomes progressively diluted due to the fluid entrainment. This study seeks to explore the ability of 2D width-averaged unsteady Reynolds-averaged Navier-Stokes (RANS simulation approach for resolving density currents in an inclined diverging channel. 2D width-averaged unsteady RANS equations closed by a buoyancy-modified − turbulence model are integrated in time with a second-order fractional step approach coupled with a direct implicit method and discretized in space on a staggered mesh using a second-order accurate finite volume approach incorporating a high-resolution semi-Lagrangian technique for the convective terms. A series of 2D width-averaged unsteady simulations is carried out for density currents. Comparisons with the experimental measurements and the other numerical simulations show that the predictions of velocity and density field are with reasonable accuracy.

  14. Thin-film Josephson junctions with alternating critical current density

    Science.gov (United States)

    Moshe, Maayan; Kogan, V. G.; Mints, R. G.

    2009-01-01

    We study the field dependence of the maximum current Im(H) in narrow edge-type thin-film Josephson junctions with alternating critical current density. Im(H) is evaluated within nonlocal Josephson electrodynamics taking into account the stray fields that affect the difference of the order-parameter phases across the junction and therefore the tunneling currents. We find that the phase difference along the junction is proportional to the applied field, depends on the junction geometry, but is independent of the Josephson critical current density gc , i.e., it is universal. An explicit form for this universal function is derived for small currents through junctions of the width W≪Λ , the Pearl length. The result is used to calculate Im(H) . It is shown that the maxima of Im(H)∝1/H and the zeros of Im(H) are equidistant but only in high fields. We find that the spacing between zeros is proportional to 1/W2 . The general approach is applied to calculate Im(H) for a superconducting quantum interference device with two narrow edge-type junctions. If gc changes sign periodically or randomly, as it does in grain boundaries of high- Tc materials and superconductor-ferromagnet-superconductor heterostructures, Im(H) not only acquires the major side peaks, but due to nonlocality the following peaks decay much slower than in bulk junctions.

  15. Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in polymer solar cells

    Energy Technology Data Exchange (ETDEWEB)

    He, Zhicai; Zhong, Chengmei; Wu, Hongbin; Su, Shijian; Cao, Yong [Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640 (China); Huang, Xun; Chen, Liwei [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou Industrial Park, Suzhou 215123 (China); Wong, Wai-Yeung [Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee, Hong Kong) and Department of Chemistry and Centre for Advanced Luminescence Materials, Hong Kong Baptist University, Waterloo Road, Hong Kong (China)

    2011-10-25

    Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in highly efficient polymer solar cells by incorporating an alcohol/water-soluble conjugated polymer as cathode interlayer is domonstrated. When combined with a low-bandgap polymer PTB7 as the electron donor material, the power efficiency of the devices is improved to certified 8.370%. Due to drastic improvement in efficiency and easy utilization, this method opens new opportunities for PSCs from various material systems to improve towards 10% efficiency. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Morphology and Density Structure of Post-CME Current Sheets

    Science.gov (United States)

    Vrsnak, B.; Poletto, G.; Vujic, E.; Vourlidas, A.

    2009-01-01

    Eruption of a coronal mass ejection (CME) is believed to drag and open the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and field relaxation by magnetic reconnection. This paper analyzes the physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to confirm whether interpreting such phenomena in terms of a reconnecting current sheet is consistent with observations. Methods: The study focuses on UVCS/SOHO and LASCO/SOHO measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of the rays implies that they are produced by Petschek-like reconnection in the large-scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km/s, and are consistent with the narrow opening-angle of rays, which add up to a few degrees. The density of rays is an order of magnitude higher than in the ambient corona. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to higher heights by the reconnection outflow.

  17. Magnetic topology and current channels in plasmas with toroidal current density inversions

    CERN Document Server

    Ciro, David

    2013-01-01

    The equilibrium magnetic field inside axisymmetric plasmas with inversions on the toroidal current density is studied. Structurally stable non-nested magnetic surfaces are considered. For any inversion in the internal current density the magnetic families define several positive current channels about a central negative one. A general expression relating the positive and negative currents is derived in terms of a topological anisotropy parameter. Next, an analytical local solution for the poloidal magnetic flux is derived and shown compatible with current hollow magnetic pitch measurements shown in the literature. Finally, the analytical solution exhibits non-nested magnetic families with positive anisotropy, indicating that the current inside the positive channels have at least twice the magnitude of the central one.

  18. Cathodic phosphate coating containing nano zinc particles on magnesium alloy

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A technology for preparation of a cathodic phosphate coating mainly containing nano metallic zinc particles and phosphate compounds on magnesium alloy was developed.The influence of cathodic current density on the microstructure of the cathodic phosphate coating Was investigated.The results show that the crystals of the coating are finer and the microstructures of the outer surface of the coatings are zigzag at the cathodic density of 0.2-0.5 A/dm2.The content of nano metallic zinc particles in the coating decreases with the increase of the thickness of the coatings and tends to be zero when the coating thickness is 4.14 μm.The cathodic phosphate coating was applied to be a transition coating for improving the adhesion between the paints and the magnesium alloys.The formation mechanism of the cathodic phosphate coating was investigated as well.

  19. Influence of operating current on the stability of deuterium arcs and hydrogen hollow cathode lamps used as background correctors in atomic absorption spectrophotometry

    International Nuclear Information System (INIS)

    The instability of deuterium arcs and hydrogen hollow cathode lamps influences significantly the reproducibility of atomic absorption measurements. The effect of current flowing through the lamp was studied as a factor influencing the stability of deuterium arcs and hydrogen lamps. Using longer integration times, it is possible to average the instability to some degree when working in the double beam mode. Considerable wavelength dependence of precision was found for both the deuterium arcs and the hydrogen hollow cathode lamps. (author)

  20. High current density, cryogenically cooled sliding electrical joint development

    International Nuclear Information System (INIS)

    In the past two years, conceptual designs for fusion energy research devices have focussed on compact, high magnetic field configurations. The concept of sliding electrical joints in the large magnets allows a number of technical advantages including enhanced mechanical integrity, remote maintainability, and reduced project cost. The rationale for sliding electrical joints is presented. The conceptual configuration for this generation of experimental devices is highlghted by an ∼ 20 T toroidal field magnet with a flat top conductor current of ∼ 300 kA and a sliding electrical joint with a gross current density of ∼ 0.6 kA/cm2. A numerical model was used to map the conductor current distribution as a function of time and position in the conductor. A series of electrical joint arrangements were produced against the system code envelope constraints for a specific version of the Ignition Studies Project (ISP) which is designated as 1025

  1. Inductive measurements of critical current density in superconducting thin films

    International Nuclear Information System (INIS)

    A noncontacting method of probing the current-induced breakdown of superconductivity (i.e., J/sub c/) in thin films is described, which makes use of a single pancake oil pressed against the film surface. The technique has a sensitivity that is approximately 100 times greater than direct transport measurements using room temperature electronics, and it eliminates many of the attendant difficulties of the latter. Preliminary results on Nb and Y-Ba-Cu-O films at 4.2 K reveal an exponential voltage-current dependence, as expected from the activated flux creep model. It is noted that, this being the case, no unique critical current density can be defined. In the case of the oxide superconductors the flux pinning parameters are such that even a practical J/sub c/ definition is probably not useful

  2. High Capacity and High Voltage Composite Oxide Cathode for Li-ion Batteries Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Currently used cathode materials in energy storage devices do not fully satisfy the power density and energy density requirements for NASA's exploration missions....

  3. Enabling aqueous binders for lithium battery cathodes - Carbon coating of aluminum current collector

    Science.gov (United States)

    Doberdò, Italo; Löffler, Nicholas; Laszczynski, Nina; Cericola, Dario; Penazzi, Nerino; Bodoardo, Silvia; Kim, Guk-Tae; Passerini, Stefano

    2014-02-01

    In this manuscript a novel approach to enable aqueous binders for lithium ion battery (LIB) cathodes is reported. Producing LiNi1/3Mn1/3Co1/3O2 (NMC) electrodes using sodium-carboxymethylcellulose (CMC) as a binder and water as a solvent, in fact, results in serious aluminum corrosion during electrode manufacturing due to the high pH of the slurry. In order to prevent the direct contact of the corrosive slurry with aluminum foil, the latter is first coated with a thin carbon layer. The CMC-based electrodes formed on carbon coated aluminum foil show enhanced performance than those made using unprotected aluminum instead. In particular, electrodes using protected aluminum foil are able to deliver a capacity of 126 mAh g-1 at 1C rate, which is rather close to that delivered by polyvinylidene-di-fluoride (PVdF)-based electrode having the same composition.

  4. 阴极保护下缝隙内的电流分布%CURRENT DISTRIBUTION IN A CATHODICALLY PROTECTED CREVICE

    Institute of Scientific and Technical Information of China (English)

    李正奉; 毛旭辉; 甘复兴

    2000-01-01

    Current distributions in a cathodically protected crevice between a simulated coating andsegmented mild steel electrodes were measured in diluted NaCl solutions. The effects of the controlpotential, solution conductivity and crevice thickness on the current distribution were studied. Theresults showed that the current distribution inside the crevice became uniform with prolonging ofpolarization time. In general, the more negative the control potential, the greater the solutionconductivity and crevice thickness, the larger the current density inside the crevice.%采用分段碳钢电极测量了稀NaCl溶液中阴极保护下模拟缝隙内的电流分布,研究了缝口控制电位、溶液电导率和缝隙宽度对电流分布的影响.结果表明在实验条件下缝隙内的电流分布随极化时间的延长而趋于均匀.溶液电导率和缝隙宽度的增大以及缝口控制电位的负移都可使缝隙内局部电流增大,阴极保护深度增大.

  5. Field emission of electrons from cathodes made of carbon fibers with a nanostructured emitting surface

    Science.gov (United States)

    Lupekhin, S. M.; Ibragimov, A. A.

    2011-06-01

    Field electron emission from cathodes made of a bunch of carbon fibers under the condition of technical vacuum is studied experimentally. A model to optimize the field emission properties of the cathode by optimizing its macrogeometry with regard to the emitting surface structure is suggested. The current-voltage characteristics of the cathode are taken in the working voltage range 1-3 kV and for anode-cathode spacings varying from 1 to 10 mm. The current density from the cathode may reach 10 A/cm2 or more.

  6. Morphology and density of post-CME current sheets

    CERN Document Server

    Vršnak, B; Vujić, E; Vourlidas, A; Ko, Y -K; Raymond, J C; Ciaravella, A; Žic, T; Webb, D F; Bemporad, A; Landini, F; Schettino, G; Jacobs, C; Suess, S T

    2009-01-01

    Eruption of a coronal mass ejection (CME) drags and "opens" the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and the field relaxation by magnetic reconnection. We analyze physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to check if the interpretation of this phenomenon in terms of reconnecting current sheet is consistent with the observations. The study is focused on measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of rays indicates that they occur as a consequence of Petschek-like reconnection in the large scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km s$^{-1}$, consistent with the narrow opening-angle of rays, adding up to a few degrees. The density of rays is an order o...

  7. High Current Density 2D/3D Esaki Tunnel Diodes

    CERN Document Server

    Krishnamoorthy, Sriram; Lee, Choong Hee; Zhang, Yuewei; McCulloch, William D; Johnson, Jared M; Hwang, Jinwoo; Wu, Yiying; Rajan, Siddharth

    2016-01-01

    The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based novel device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area, Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current density of 446 A/cm2 with repeatable room temperature negative differential resistance, peak to valley current ratio of 1.2, and minimal hysteresis was measured in the MoS2/GaN non-epitaxial tunnel diode. A high current density of 1 kA/cm2 was measured in the Zener mode (reverse bias) at -1 V bias. The GaN/MoS2 tunnel junction was also modeled by treating MoS2 as a bulk semiconductor, and the electrostatics at the 2D/3D interface was found to be crucial in explaining the experimentally observed device characteristics.

  8. High Current Density 2D/3D Esaki Tunnel Diodes

    OpenAIRE

    Krishnamoorthy, Sriram; Lee II, Edwin W.; Lee, Choong Hee; Zhang, Yuewei; McCulloch, William D.; Johnson, Jared M.; Hwang, Jinwoo; Wu, Yiying; Rajan, Siddharth

    2016-01-01

    The integration of two-dimensional materials such as transition metal dichalcogenides with bulk semiconductors offer interesting opportunities for 2D/3D heterojunction-based novel device structures without any constraints of lattice matching. By exploiting the favorable band alignment at the GaN/MoS2 heterojunction, an Esaki interband tunnel diode is demonstrated by transferring large area, Nb-doped, p-type MoS2 onto heavily n-doped GaN. A peak current density of 446 A/cm2 with repeatable roo...

  9. The current density in quantum electrodynamics in external potentials

    CERN Document Server

    Schlemmer, Jan

    2015-01-01

    We review different definitions of the current density for quantized fermions in the presence of an external electromagnetic field. Several deficiencies in the popular prescription due to Schwinger and the mode sum formula for static external potentials are pointed out. We argue that Dirac's method, which is the analog of the Hadamard point-splitting employed in quantum field theory in curved space-times, is conceptually the most satisfactory. As a concrete example, we discuss vacuum polarization and the stress-energy tensor for massless fermions in 1+1 dimension. Also a general formula for the vacuum polarization in static external potentials in 3+1 dimensions is derived.

  10. The current density in quantum electrodynamics in external potentials

    Science.gov (United States)

    Schlemmer, Jan; Zahn, Jochen

    2015-08-01

    We review different definitions of the current density for quantized fermions in the presence of an external electromagnetic field. Several deficiencies in the popular prescription due to Schwinger and the mode sum formula for static external potentials are pointed out. We argue that Dirac's method, which is the analog of the Hadamard point-splitting employed in quantum field theory in curved space-times, is conceptually the most satisfactory. As a concrete example, we discuss vacuum polarization and the stress-energy tensor for massless fermions in 1+1 dimension. Also a general formula for the vacuum polarization in static external potentials in 3+1 dimensions is derived.

  11. Control of the charge and the nonlinear oscillation of dust particles by alternating current voltage superposition on the cathode in a direct current discharge

    International Nuclear Information System (INIS)

    Experimental and theoretical studies were conducted to investigate the control of charge and modification of nonlinear oscillations of externally injected dust particles in a dc discharge. The superposition of ac voltage on a dc cathode led to plasma density modulation, which brought about a drastic change of particle oscillation characteristics. Examples of the changes include disappearance of the subharmonic resonance peak and hysteresis as the ac superposition voltage was increased, which is attributed to the fact that the ac superposition made sheath structure less nonlinear and less parametrically resonant. In addition, as the ac frequency decreased from 5 kHz to 1 kHz at the same ac voltage (15 V), the subharmonic peak became weakened along with its frequency. This result demonstrates that the dust charge is the main parameter in determining occurrence of the subharmonic resonance peak. We consequently expect that modification of the oscillation dynamics of dust particles and furthermore the separate control of the charge may be possible by the ac modulation of the dc biased cathode

  12. Cathodic Protection Model Facility

    Data.gov (United States)

    Federal Laboratory Consortium — FUNCTION: Performs Navy design and engineering of ship and submarine impressed current cathodic protection (ICCP) systems for underwater hull corrosion control and...

  13. Study of electron current extraction from a radio frequency plasma cathode designed as a neutralizer for ion source applications

    Energy Technology Data Exchange (ETDEWEB)

    Jahanbakhsh, Sina, E-mail: sinajahanbakhsh@gmail.com; Satir, Mert; Celik, Murat [Department of Mechanical Engineering, Bogazici University, Istanbul 34342 (Turkey)

    2016-02-15

    Plasma cathodes are insert free devices that are developed to be employed as electron sources in electric propulsion and ion source applications as practical alternatives to more commonly used hollow cathodes. Inductively coupled plasma cathodes, or Radio Frequency (RF) plasma cathodes, are introduced in recent years. Because of its compact geometry, and simple and efficient plasma generation, RF plasma source is considered to be suitable for plasma cathode applications. In this study, numerous RF plasma cathodes have been designed and manufactured. Experimental measurements have been conducted to study the effects of geometric and operational parameters. Experimental results of this study show that the plasma generation and electron extraction characteristics of the RF plasma cathode device strongly depend on the geometric parameters such as chamber diameter, chamber length, orifice diameter, orifice length, as well as the operational parameters such as RF power and gas mass flow rate.

  14. Current density fluctuations, nonlinear coupling, and transport in MST

    Energy Technology Data Exchange (ETDEWEB)

    Prager, S.C.; Almagri, A.F.; Assadi, S.; Cekic, M.; Chapman, B.E.; Crocker, N.; Den Hartog, D.J.; Dexter, R.N.; Fiksel, G.; Fonck, R.J.; Henry, J.S.; Hokin, S.A.; Holly, D.J.; Ji, H.; Rempel, T.D.; Sarff, J.S.; Scime, E.; Shen, W.; Sidikman, K.L.; Sprott, J.C.; Stoneking, M.R.; Watts, C.

    1992-09-01

    New information on magnetic fluctuations and transport in toroidal devices has been obtained in the MST reversed field pinch through measurement of nonlinear coupling of three waves in k-space, and measurement of current density fluctuations. Measurements of nonlinear coupling of magnetic fluctuations reveals that (1) two poloidal mode number m = 1 modes couple strongly to an m = 2 mode, (2) toroidal mode coupling is broad extending up to n = 20, (3) these features agree with predictions for tearing fluctuations from a nonlinear MHD code, (4) during a sawtooth crash the number of modes involved in nonlinear interactions increases dramatically and the k-spectrum broadens simultaneously. Measurements of current density fluctuations over the outer 20% of the minor radius reveal that (1) low frequency fluctuations are consistent with tearing modes, (2) high frequency fluctuations are localized turbulence which maintains resonance with the equilibrium field as q changes with radius, (3) particle transport from magnetic fluctuations is ambipolar (i.e., <{delta}j{sub {parallel}}B{sub r}> = O).

  15. MHD Modeling of Conductors at Ultra-High Current Density

    Energy Technology Data Exchange (ETDEWEB)

    Asay, J.R.; Desjarlais, M.P.; Douglas, M.R.; Frese, M.H.; Hall, C.A.; Morse, R.L.; Reisman, D.; Rosenthal, S.E.; Spielman, R.B.; Stygar, W.A.

    1999-06-30

    In conjunction with ongoing high-current experiments on Sandia National Laboratories' Z accelerator we have revisited a problem first described in detail by Heinz Knoepfel. MITLs of previous pulsed power accelerators have been in the 1-Tesla regime. Z's disc transmission line (downstream of the current addition) is in a 100-1200 Tesla regime, so its conductors cannot be modeled simply as static infinite conductivity boundaries. Using the MHD code MACH2 we have been investigating conductor hydrodynamics, characterizing the joule heating, magnetic field diffusion, and material deformation, pressure, and velocity over a range of current densities, current rise-times, and conductor materials. Three purposes of this work are ( 1) to quantify power flow losses owing to ultra-high magnetic fields, (2) to model the response of VISAR diagnostic samples in various configurations on Z, and (3) to incorporate the most appropriate equation of state and conductivity models into our MHD computations. Certain features are strongly dependent on the details of the conductivity model. Comparison with measurements on Z will be discussed.

  16. MHD Modeling of Conductors at Ultra-High Current Density

    International Nuclear Information System (INIS)

    In conjunction with ongoing high-current experiments on Sandia National Laboratories' Z accelerator, the authors have revisited a problem first described in detail by Heinz Knoepfel. Unlike the 1-Tesla MITLs of pulsed power accelerators used to produce intense particle beams, Z's disc transmission line (downstream of the current addition) is in a 100--1,200 Tesla regime, so its conductors cannot be modeled simply as static infinite conductivity boundaries. Using the MHD code MACH2 they have been investigating the conductor hydrodynamics, characterizing the joule heating, magnetic field diffusion, and material deformation, pressure, and velocity over a range of current densities, current rise-times, and conductor materials. Three purposes of this work are (1) to quantify power flow losses owing to ultra-high magnetic fields, (2) to model the response of VISAR diagnostic samples in various configurations on Z, and (3) to incorporate the most appropriate equation of state and conductivity models into the MHD computations. Certain features are strongly dependent on the details of the conductivity model

  17. Comparative simulation studies of plasma cathode electron (PCE) gun

    International Nuclear Information System (INIS)

    Pseudospark discharge based plasma cathode has capability to provide high current density electron beam during discharge process. In this paper an effort has been made to simulate the breakdown processes in the pseudospark discharge based plasma cathode electron gun. The two-dimensional plasma simulation codes VORPAL and OOPIC-Pro have been used and results are compared. The peak discharge current in the plasma cathode electron gun is found to be dependent on aperture size, hollow cathode dimensions, anode voltage and seed electrons energy. The effect of these design parameters on the peak anode current has been analysed by both the codes and results matches well within 10% variation. For the seed electron generation an electron beam trigger source is used to control the discharge process in the hollow cathode cavity. The time span of trigger source has been varied from 1-100 ns to analyze the effect on the peak anode current.

  18. Efficient Reduction of CO2 to CO with High Current Density Using in Situ or ex Situ Prepared Bi-Based Materials

    OpenAIRE

    Medina-Ramos, Jonnathan; DiMeglio, John L.; Rosenthal, Joel

    2014-01-01

    The development of inexpensive electrocatalysts that can promote the reduction of CO2 to CO with high selectivity, efficiency, and large current densities is an important step on the path to renewable production of liquid carbon-based fuels. While precious metals such as gold and silver have historically been the most active cathode materials for CO2 reduction, the price of these materials precludes their use on the scale required for fuel production. Bismuth, by comparison, is an affordable ...

  19. Ion bombardment investigations of impregnated cathodes

    Science.gov (United States)

    Zhang, Xiaobing; Gaertner, Georg

    2003-06-01

    Ion bombardment is one of the important factors limiting the performance of impregnated cathodes (=Ba dispenser cathodes) in high end television tubes or in colour monitor tubes. Hence, when designing a new gun with, e.g. higher electron beam current density, it is important also to model the influence of ion bombardment. Therefore, relations between basic parameters as a function of temperature need to be known quantitatively. In this paper, the emission slump of impregnated cathodes has been analyzed in a diode configuration in UHV with a differentially pumped Ar ion gun. The emission degeneration during and regeneration periods after ion bombardment have been investigated as function of cathode temperature, ion current and ion energy. One of the important results is, that the degeneration time coefficient is only weakly dependent on ion energy. The data matrix obtained can be used to improve the ion bombardment model applied in new electron gun design.

  20. Ion bombardment investigations of impregnated cathodes

    International Nuclear Information System (INIS)

    Ion bombardment is one of the important factors limiting the performance of impregnated cathodes (=Ba dispenser cathodes) in high end television tubes or in colour monitor tubes. Hence, when designing a new gun with, e.g. higher electron beam current density, it is important also to model the influence of ion bombardment. Therefore, relations between basic parameters as a function of temperature need to be known quantitatively. In this paper, the emission slump of impregnated cathodes has been analyzed in a diode configuration in UHV with a differentially pumped Ar ion gun. The emission degeneration during and regeneration periods after ion bombardment have been investigated as function of cathode temperature, ion current and ion energy. One of the important results is, that the degeneration time coefficient is only weakly dependent on ion energy. The data matrix obtained can be used to improve the ion bombardment model applied in new electron gun design

  1. Critical current density and current distribution in field cooled superconducting disks

    Science.gov (United States)

    Bernstein, Pierre; Noudem, Jacques; Dupont, Louis

    2016-07-01

    Applications of bulk superconductors concern superconducting motors and generators, the levitation of vehicles, the generation of high magnetic fields with small size cryo-magnets, the shielding of magnetic fields and other applications. For all of them, it is essential to determine the critical current density, and to understand the effect of the shape and size of the bulks on the properties of interest. In this contribution, we show how the combination of levitation force and trapped field measurements allow one to determine the characteristics and the potential performances of superconducting disks using analytical modeling. As examples of applications we detail the effects of the magnetizing field and of the bulk sheet critical current density on the levitation force. An important result of the reported measurements is that in field-cooled samples, the shielding currents possibly do not flow along the whole thickness of the disks.

  2. Spin-Density Functionals from Current-Density Functional Theory and Vice Versa: A Road towards New Approximations

    International Nuclear Information System (INIS)

    It is shown that the exchange-correlation functional of spin-density functional theory is identical, on a certain set of densities, with the exchange-correlation functional of current-density functional theory. This rigorous connection is used to construct new approximations of the exchange-correlation functionals. These include a conceptually new generalized-gradient spin-density functional and a nonlocal current-density functional. copyright 1997 The American Physical Society

  3. Characterization of Hollow Cathode Performance and Thermal Behavior

    Science.gov (United States)

    Polk, James E.; Goebel, Dan M.; Watkins, Ron; Jameson, Kristina; Yoneshige, Lance; Przybylowski, JoHanna; Cho, Lauren

    2006-01-01

    Hollow cathodes are one of the main life-limiting components in ion engines and Hall thrusters. Although state-of-the-art hollow cathodes have demonstrated up to 30,352 hours of operation in ground tests with careful handling, future missions are likely to require longer life, more margin and greater resistance to reactive contaminant gases. Three alternate hollow cathode technologies that exploit different emitter materials or geometries to address some of the limitations of state-of-the-art cathodes are being investigated. Performance measurements of impregnated tungsten-iridium dispenser cathodes at discharge currents of 4 to 15 A demonstrated that they have the same operating range and ion production efficiency as conventional tungsten dispenser cathodes. Temperature measurements indicated that tungsten-iridium cathodes also operate at the same emitter temperatures. They did not exhibit the expected reduction in work function at the current densities tested. Hollow cathodes with lanthanum hexaboride emitters operated over a wide current range, but suffered from lower ion production efficiency at currents below about 12.4 A because of higher insert heating requirements. Differences in operating voltages and ion production rates are explained with a simple model of the effect of cathode parameters on discharge behavior.

  4. The effect of cathode bias (field effect) on the surface leakage current of CdZnTe detectors

    DEFF Research Database (Denmark)

    Bolotnikov, A.E.; Chen, C.M.H.; Cook, W.R.;

    2003-01-01

    Surface resistivity is an important parameter of multi-electrode CZT detectors such as coplanar-grid, strip, or pixel detectors. Low surface resistivity results in a high leakage current and affects the charge collection efficiency in the areas near contacts. Thus, it is always desirable to have...... the surface resistivity of the detector as high as possible. In the past the most significant efforts were concentrated to develop passivation techniques for CZT detectors. However, as we found, the field-effect caused by a bias applied on the cathode can significantly reduce the surface resistivity even...... though the detector surface was carefully passivated. In this paper we illustrate that the field-effect is a common feature of the CZT multi-electrode detectors, and discuss how to take advantage of this effect to improve the surface resistivity of CZT detectors....

  5. Influences of arc current on composition and properties of MgO thin films prepared by cathodic vacuum arc deposition

    International Nuclear Information System (INIS)

    MgO thin films with high optical transmittances (more than 90%) were prepared by cathodic vacuum arc deposition technique. With the increase of arc current from 40 to 80 A, the deposition pressure decreases and the film thickness increases; the atomic ratio of Mg/O in MgO thin films (obtained by RBS) increases from 0.97 to 1.17, giving that deposited at 50 A most close to the stoichiometric composition of the bulk MgO; the grains of MgO thin films grow gradually as shown in SEM images. XRD patterns show that MgO (1 1 0) orientation is predominant for films prepared at the arc currents ranged from 50 to 70 A. The MgO (1 0 0) orientation is much enhanced and comparable to that of MgO (1 1 0) for films prepared at the arc current of 80 A. The secondary electron emission coefficient of MgO thin film increases with arc current ranged from 50 to 70 A.

  6. Critical state model with anisotropic critical current density

    CERN Document Server

    Bhagwat, K V; Ravikumar, G

    2003-01-01

    Analytical solutions of Bean's critical state model with critical current density J sub c being anisotropic are obtained for superconducting cylindrical samples of arbitrary cross section in a parallel geometry. We present a method for calculating the flux fronts and magnetization curves. Results are presented for cylinders with elliptical cross section with a specific form of the anisotropy. We find that over a certain range of the anisotropy parameter the flux fronts have shapes similar to those for an isotropic sample. However, in general, the presence of anisotropy significantly modifies the shape of the flux fronts. The field for full flux penetration also depends on the anisotropy parameter. The method is extended to the case of anisotropic J sub c that also depends on the local field B, and magnetization hysteresis curves are presented for typical values of the anisotropy parameter for the case of |J sub c | that decreases exponentially with |B|.

  7. Development of high temperature superconductors having high critical current density

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Gye Wong; Kim, C. J.; Lee, H.G.; Kwon, S. C.; Lee, H. J.; Kim, K. B.; Park, J. Y.; Jung, C. H

    2000-08-01

    Fabrication of high T{sub c} superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm{sup 2} and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation.

  8. Development of high temperature superconductors having high critical current density

    International Nuclear Information System (INIS)

    Fabrication of high Tc superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm2 and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation

  9. Identifying Distinguishing Characteristics of Secondary Pyroclastic Density Currents

    Science.gov (United States)

    Isom, S. L.; Brand, B. D.

    2014-12-01

    Pyroclastic density currents (PDCs) are ground-hugging mixtures of volcanic particles and gas that travel down the slopes of erupting volcanoes. The combination of high velocities, high bulk densities (due to particles in the current) and high temperatures make PDCs the most dangerous and deadly hazard associated with explosive volcanism. Secondary explosive phenomenon associated with PDCs, such as inland-directed surges (e.g., Montserrat, 2003) and phreatic explosions (e.g., Mt St Helens 1980) can increase the area affected and duration of the hazard. However, little work has been done on distinguishing the deposits of secondary explosive phenomenon from primary phenomenon. Samples have been acquired from the 1980 Mt St Helens phreatic explosion crater deposits and the 2003 eruptive event at Montserrat where a PDC flowed into the ocean, causing an inland-directed surge (Edmonds and Herd, 2005. Geology 33.4:245-248). The samples will be analyzed via depositional characteristics, granulometry, componentry, microscopic analysis and scanning electron microscope imaging. We hypothesize that thermal cracking or vesicle distortion (e.g., compression or hindered expansion) may occur in hot pyroclasts that enter a body of water, leading to a difference between the ash textures of primary PDCs, phreatic surges and inland-directed surge deposits. Analyzing granulometry and componentry from parent flows and secondary flows may also reveal distinguishing characteristics that will allow us to constrain differences in segregation mechanisms of particles for each phenomenon. Determining distinguishing depositional characteristics of these secondary phenomena is important for assessing their occurrence during past eruptions and identifying conditions conducive to the formation of secondary explosions. This will result in the ability to make more accurate hazard maps for volcanoes prone to explosive activity.

  10. Fusion-reaction-yield scaling with PF plasma current density

    Energy Technology Data Exchange (ETDEWEB)

    Bortolotti, A.; Mezzetti, F.; Montanari, T. [Univ. of Ferrara (Italy); Nardi, V.; Powell, C.W. [Stevens Inst. of Tech., Hoboken, NJ (United States)

    1995-12-31

    The scaling of the neutron yield Y from D + D reactions and, specifically, of its fluctuations {Delta}Y from discharge to discharge was experimentally determined with four plasma focus machines, as function of the peak plasma-current density J. The powering energy levels were W = 6 kJ for one PF machine (PF{sub 1}) 20 kJ for two identical PF machines 35 kJ and 50 kJ for a fourth machine (PF{sub 4}). The comparative tests at 20 kJ and 35 kJ had the same peak electrode current I = 1 MA, the same charging voltage of the capacitor bank 25 kV, the same ratio inductance/capacitance (L/C), but with C(PF{sub 4}) = 2C(PF{sub 2}) and L(PF{sub 4}) {equivalent_to} [T(PF{sub 4})/2{pi}]{sup 2}/C(PF{sub 4}) = 2L(PF{sub 2}). T(PF{sub 4}) {approx_equal} 1.4T(PF{sub 2}), is the measured period of the complete PF electric circuit, including the propagating current sheet between coaxial electrodes. The bearing on Y, {Delta}Y of the breech overvoltage during the pinch collapse and of the variations of J is experimentally determined. The data indicate that MaxY(PF{sub 4}) {approx_equal} mean value Y{sub Av}(PF{sub 2}) of Y, Y{sub Av}(PF{sub 2}) {approx_equal} 3Y{sub Av}(PF{sub 3}). The neural network analysis connecting Y and the current sheet multiplicity in the same discharge, was carried out as in earlier experiments.

  11. Fusion-reaction-yield scaling with PF plasma current density

    International Nuclear Information System (INIS)

    The scaling of the neutron yield Y from D + D reactions and, specifically, of its fluctuations ΔY from discharge to discharge was experimentally determined with four plasma focus machines, as function of the peak plasma-current density J. The powering energy levels were W = 6 kJ for one PF machine (PF1) 20 kJ for two identical PF machines 35 kJ and 50 kJ for a fourth machine (PF4). The comparative tests at 20 kJ and 35 kJ had the same peak electrode current I = 1 MA, the same charging voltage of the capacitor bank 25 kV, the same ratio inductance/capacitance (L/C), but with C(PF4) = 2C(PF2) and L(PF4) ≡ [T(PF4)/2π]2/C(PF4) = 2L(PF2). T(PF4) ≅ 1.4T(PF2), is the measured period of the complete PF electric circuit, including the propagating current sheet between coaxial electrodes. The bearing on Y, ΔY of the breech overvoltage during the pinch collapse and of the variations of J is experimentally determined. The data indicate that MaxY(PF4) ≅ mean value YAv(PF2) of Y, YAv(PF2) ≅ 3YAv(PF3). The neural network analysis connecting Y and the current sheet multiplicity in the same discharge, was carried out as in earlier experiments

  12. A hollow cathode hydrogen ion source. [for controlled fusion

    Science.gov (United States)

    Sovey, J. S.; Mirtich, M. J.

    1977-01-01

    High current density ion sources have been used to heat plasmas in controlled thermonuclear reaction experiments. High beam currents imply relatively high emission currents from cathodes which have generally taken the form of tungsten filaments. This paper describes a hydrogen ion source which was primarily developed to assess the emission current capability and design requirements for hollow cathodes for application in neutral injection devices. The hydrogen source produced ions by electron bombardment via a single hollow cathode. Source design followed mercury ion thruster technology, using a weak magnetic field to enhance ionization efficiency. A 1.3-cm-diam hollow cathode using a low work function material dispenser performed satisfactorily over a discharge current range of 10-90 A. Cylindrical probe measurements taken without ion extraction indicate maximum ion number densities on the order of 10 trillion/cu cm. Discharge durations ranged from 30 sec to continuous operation. Tests with beam extraction at 2.5 keV and 30 A discharge current yield average ion beam current densities of 0.1 A/sq cm over a 5-cm extraction diameter. Results of this study can be used to supply the baseline information needed to scale hollow cathodes for operation at discharge currents of hundreds of amperes using distributed cathodes.

  13. Theory of electron current filamentation instability and ion density filamentation in the early development of a DPF discharge

    International Nuclear Information System (INIS)

    Two-dimensional simulations of the initial stages of plasma formation in a dense plasma focus show the formation, in a few tens of nanoseconds, of a dense layer of plasma (ne∼1018 cm-3,Te∼3 eV) in a thin layer surrounding the insulator-covered central anode of the focus device, and carrying axially-directed current at rather high current density.Earlier work on the filamentation of dense cathode plasma in high-power diodes seems to indicate that the anode plasma current layer in a dense plasma focus (DPF) device could be subject to the same instability, creating a growth of axially-directed filaments in the current density. The growth rate for resistive-thermal-driven filamentation, e.g. at 30 torr and ∼3 eV electron temperature, exceeds the that due to non-thermal current (JxB) driving, and is determined by electron dynamics, so its evolution is quicker than the response-time of the ions.Nonetheless, with such a growing current-density perturbation as a seed and its increasing rippling of the azimuthal magnetic field as a driver, the ions will eventually take part in the azimuthal bunching, forming filaments in the ion density as well. The resistive-thermal-driven filamentation fields thus serve to ''hurry-up'' the development of ion density filamentation, as shown approximately in the work presented here. This theory predicts, for light ions, a relatively early (≤250 ns) development of visible filaments along the anode, perhaps even before the main rundown phase of the focus plasma motion, and these filaments may persist during the 'liftoff' phase of the current layer to form the rundown phase of the plasma front. This work is supported by Larwenceville Plasma Physics.

  14. Enhancement in field emission current density of Ni nanoparticles embedded in thin silica matrix by swift heavy ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Sarker, Debalaya; Patra, Rajkumar; Srivastava, P.; Ghosh, S., E-mail: santanu1@physics.iitd.ac.in [Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India); Kumar, H. [Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India); Instituto de Física, Universidade de São Paulo, USP, 05508-090 São Paulo, SP (Brazil); Kabiraj, D.; Avasthi, D. K. [Inter University Accelerator Centre, New Delhi 110067 (India); Vayalil, Sarathlal K.; Roth, S. V. [DESY, Petra III, Hamburg (Germany)

    2014-05-07

    The field emission (FE) properties of nickel nanoparticles embedded in thin silica matrix irradiated with 100 MeV Au{sup +7} ions at various fluences are studied here. A large increase in FE current density is observed in the irradiated films as compared to their as deposited counterpart. The dependence of FE properties on irradiation fluence is correlated with surface roughness, density of states of valence band and size distribution of nanoparticles as examined with atomic force microscope, X-ray photoelectron spectroscopy, and grazing incidence small angle x-ray scattering. A current density as high as 0.48 mA/cm{sup 2} at an applied field 15 V/μm has been found for the first time for planar field emitters in the film irradiated with fluence of 5.0 × 10{sup 13} ions/cm{sup 2}. This significant enhancement in the current density is attributed to an optimized size distribution along with highest surface roughness of the same. This new member of field emission family meets most of the requirements of cold cathodes for vacuum micro/nanoelectronic devices.

  15. Barium-Dispenser Thermionic Cathode

    Science.gov (United States)

    Wintucky, Edwin G.; Green, M.; Feinleib, M.

    1989-01-01

    Improved reservoir cathode serves as intense source of electrons required for high-frequency and often high-output-power, linear-beam tubes, for which long operating lifetime important consideration. High emission-current densities obtained through use of emitting surface of relatively-low effective work function and narrow work-function distribution, consisting of coat of W/Os deposited by sputtering. Lower operating temperatures and enhanced electron emission consequently possible.

  16. Energetic high current density electron/ion beam generation in plasma opening switches

    International Nuclear Information System (INIS)

    Experimental results on the generation of high energy ion/electron beams during operation of microsecond/nanosecond Plasma Opening Switch (POS) are presented. For the nanosecond POS, a coaxial configuration with negatively charged central electrode was used. For the microsecond POS, a strip-line geometry was investigated. Different arrays of magnetically insulated Collimated Faraday Cups (CFC) were used to observe energetic electron/ion flows towards the anode/cathode POS electrodes and towards the load. It was shown that in both nanosecond and microsecond cases, high-energy high current density axial ion flows are generated downstream towards the load at the load side edge of the plasma. The main axial ion acceleration occurs in the first few cm downstream with respect to the load side edge of the plasma at the beginning of the POS opening. Data observed by the anode CFC array show fast axial propagation of a radial electron flow along the anode electrode towards the load which is accompanied by an ion flow that first appears at the generator side of the plasma. (author). 10 figs., 10 refs

  17. Improved Dispenser Cathodes

    Science.gov (United States)

    Ives, R. Lawrence; Falce, Lou

    2006-01-01

    Variations in emission current from dispenser cathodes can be caused by variations in temperature and work function over the surface. This paper described research to reduce these variations using improved mechanical designs and controlled porosity cathodes made from sintered tungsten wires. The program goal is to reduce current emission variations to less than 5% over the surface of magnetron injection guns operating temperature limited.

  18. Orbital functionals in density-matrix- and current-density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Helbig, N.

    2006-05-15

    Density-Functional Theory (DFT), although widely used and very successful in the calculation of several observables, fails to correctly describe strongly correlated materials. In the first part of this work we, therefore, introduce reduced-densitymatrix- functional theory (RDMFT) which is one possible way to treat electron correlation beyond DFT. Within this theory the one-body reduced density matrix (1- RDM) is used as the basic variable. Our main interest is the calculation of the fundamental gap which proves very problematic within DFT. In order to calculate the fundamental gap we generalize RDMFT to fractional particle numbers M by describing the system as an ensemble of an N and an N+1 particle system (with N{<=}M{<=}N+1). For each fixed particle number, M, the total energy is minimized with respect to the natural orbitals and their occupation numbers. This leads to the total energy as a function of M. The derivative of this function with respect to the particle number has a discontinuity at integer particle number which is identical to the gap. In addition, we investigate the necessary and sufficient conditions for the 1- RDM of a system with fractional particle number to be N-representable. Numerical results are presented for alkali atoms, small molecules, and periodic systems. Another problem within DFT is the description of non-relativistic many-electron systems in the presence of magnetic fields. It requires the paramagnetic current density and the spin magnetization to be used as basic variables besides the electron density. However, electron-gas-based functionals of current-spin-density-functional Theory (CSDFT) exhibit derivative discontinuities as a function of the magnetic field whenever a new Landau level is occupied, which makes them difficult to use in practice. Since the appearance of Landau levels is, intrinsically, an orbital effect it is appealing to use orbital-dependent functionals. We have developed a CSDFT version of the optimized

  19. Variation of eddy current density distribution and its effect on crack signal in eddy current non-destructive of testing

    OpenAIRE

    Ladislav Janousek

    2006-01-01

    The paper deals with variation of eddy current density distribution along material depth and investigates an effect of the variation on a crack signal in eddy current non-destructive testing. Four coaxial rectangular tangential coils are used to induce eddy currents in a tested conductive object. The exciting coils are driven independently by phase-shifted AC currents; a ratio of amplitudes of the exciting currents is continuously changed to vary the distribution of eddy current density along...

  20. The effect of cathode geometry on barium transport in hollow cathode plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Polk, James E., E-mail: james.e.polk@jpl.nasa.gov; Mikellides, Ioannis G.; Katz, Ira [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109 (United States); Capece, Angela M. [California Institute of Technology, 1200 E. California Blvd., Pasadena, California 91125 (United States)

    2014-05-14

    The effect of barium transport on the operation of dispenser hollow cathodes was investigated in numerical modeling of a cathode with two different orifice sizes. Despite large differences in cathode emitter temperature, emitted electron current density, internal xenon neutral and plasma densities, and size of the plasma-surface interaction region, the barium transport in the two geometries is qualitatively very similar. Barium is produced in the insert and flows to the surface through the porous structure. A buildup of neutral Ba pressure in the plasma over the emitter surface can suppress the reactions supplying the Ba, restricting the net production rate. Neutral Ba flows into the dense Xe plasma and has a high probability of being ionized at the periphery of this zone. The steady state neutral Ba density distribution is determined by a balance between pressure gradient forces and the drag force associated with collisions between neutral Ba and neutral Xe atoms. A small fraction of the neutral Ba is lost upstream. The majority of the neutral Ba is ionized in the high temperature Xe plasma and is pushed back to the emitter surface by the electric field. The steady state Ba{sup +} ion density distribution results from a balance between electrostatic and pressure forces, neutral Xe drag and Xe{sup +} ion drag with the dominant forces dependent on location in the discharge. These results indicate that hollow cathodes are very effective at recycling Ba within the discharge and therefore maintain a high coverage of Ba on the emitter surface, which reduces the work function and sustains high electron emission current densities at moderate temperatures. Barium recycling is more effective in the cathode with the smaller orifice because the Ba is ionized in the dense Xe plasma concentrated just upstream of the orifice and pushed back into the hollow cathode. Despite a lower emitter temperature, the large orifice cathode has a higher Ba loss rate through the orifice

  1. The effect of cathode geometry on barium transport in hollow cathode plasmas

    International Nuclear Information System (INIS)

    The effect of barium transport on the operation of dispenser hollow cathodes was investigated in numerical modeling of a cathode with two different orifice sizes. Despite large differences in cathode emitter temperature, emitted electron current density, internal xenon neutral and plasma densities, and size of the plasma-surface interaction region, the barium transport in the two geometries is qualitatively very similar. Barium is produced in the insert and flows to the surface through the porous structure. A buildup of neutral Ba pressure in the plasma over the emitter surface can suppress the reactions supplying the Ba, restricting the net production rate. Neutral Ba flows into the dense Xe plasma and has a high probability of being ionized at the periphery of this zone. The steady state neutral Ba density distribution is determined by a balance between pressure gradient forces and the drag force associated with collisions between neutral Ba and neutral Xe atoms. A small fraction of the neutral Ba is lost upstream. The majority of the neutral Ba is ionized in the high temperature Xe plasma and is pushed back to the emitter surface by the electric field. The steady state Ba+ ion density distribution results from a balance between electrostatic and pressure forces, neutral Xe drag and Xe+ ion drag with the dominant forces dependent on location in the discharge. These results indicate that hollow cathodes are very effective at recycling Ba within the discharge and therefore maintain a high coverage of Ba on the emitter surface, which reduces the work function and sustains high electron emission current densities at moderate temperatures. Barium recycling is more effective in the cathode with the smaller orifice because the Ba is ionized in the dense Xe plasma concentrated just upstream of the orifice and pushed back into the hollow cathode. Despite a lower emitter temperature, the large orifice cathode has a higher Ba loss rate through the orifice because the Xe

  2. The effect of cathode geometry on barium transport in hollow cathode plasmas

    Science.gov (United States)

    Polk, James E.; Mikellides, Ioannis G.; Capece, Angela M.; Katz, Ira

    2014-05-01

    The effect of barium transport on the operation of dispenser hollow cathodes was investigated in numerical modeling of a cathode with two different orifice sizes. Despite large differences in cathode emitter temperature, emitted electron current density, internal xenon neutral and plasma densities, and size of the plasma-surface interaction region, the barium transport in the two geometries is qualitatively very similar. Barium is produced in the insert and flows to the surface through the porous structure. A buildup of neutral Ba pressure in the plasma over the emitter surface can suppress the reactions supplying the Ba, restricting the net production rate. Neutral Ba flows into the dense Xe plasma and has a high probability of being ionized at the periphery of this zone. The steady state neutral Ba density distribution is determined by a balance between pressure gradient forces and the drag force associated with collisions between neutral Ba and neutral Xe atoms. A small fraction of the neutral Ba is lost upstream. The majority of the neutral Ba is ionized in the high temperature Xe plasma and is pushed back to the emitter surface by the electric field. The steady state Ba+ ion density distribution results from a balance between electrostatic and pressure forces, neutral Xe drag and Xe+ ion drag with the dominant forces dependent on location in the discharge. These results indicate that hollow cathodes are very effective at recycling Ba within the discharge and therefore maintain a high coverage of Ba on the emitter surface, which reduces the work function and sustains high electron emission current densities at moderate temperatures. Barium recycling is more effective in the cathode with the smaller orifice because the Ba is ionized in the dense Xe plasma concentrated just upstream of the orifice and pushed back into the hollow cathode. Despite a lower emitter temperature, the large orifice cathode has a higher Ba loss rate through the orifice because the Xe

  3. Adult subependymal neural precursors, but not differentiated cells, undergo rapid cathodal migration in the presence of direct current electric fields.

    Directory of Open Access Journals (Sweden)

    Robart Babona-Pilipos

    Full Text Available BACKGROUND: The existence of neural stem and progenitor cells (together termed neural precursor cells in the adult mammalian brain has sparked great interest in utilizing these cells for regenerative medicine strategies. Endogenous neural precursors within the adult forebrain subependyma can be activated following injury, resulting in their proliferation and migration toward lesion sites where they differentiate into neural cells. The administration of growth factors and immunomodulatory agents following injury augments this activation and has been shown to result in behavioural functional recovery following stroke. METHODS AND FINDINGS: With the goal of enhancing neural precursor migration to facilitate the repair process we report that externally applied direct current electric fields induce rapid and directed cathodal migration of pure populations of undifferentiated adult subependyma-derived neural precursors. Using time-lapse imaging microscopy in vitro we performed an extensive single-cell kinematic analysis demonstrating that this galvanotactic phenomenon is a feature of undifferentiated precursors, and not differentiated phenotypes. Moreover, we have shown that the migratory response of the neural precursors is a direct effect of the electric field and not due to chemotactic gradients. We also identified that epidermal growth factor receptor (EGFR signaling plays a role in the galvanotactic response as blocking EGFR significantly attenuates the migratory behaviour. CONCLUSIONS: These findings suggest direct current electric fields may be implemented in endogenous repair paradigms to promote migration and tissue repair following neurotrauma.

  4. Development of plasma cathode electron guns

    Science.gov (United States)

    Oks, Efim M.; Schanin, Peter M.

    1999-05-01

    The status of experimental research and ongoing development of plasma cathode electron guns in recent years is reviewed, including some novel upgrades and applications to various technological fields. The attractiveness of this kind of e-gun is due to its capability of creating high current, broad or focused beams, both in pulsed and steady-state modes of operation. An important characteristic of the plasma cathode electron gun is the absence of a thermionic cathode, a feature which leads to long lifetime and reliable operation even in the presence of aggressive background gas media and at fore-vacuum gas pressure ranges such as achieved by mechanical pumps. Depending on the required beam parameters, different kinds of plasma discharge systems can be used in plasma cathode electron guns, such as vacuum arcs, constricted gaseous arcs, hollow cathode glows, and two kinds of discharges in crossed E×B fields: Penning and magnetron. At the present time, plasma cathode electron guns provide beams with transverse dimension from fractional millimeter up to about one meter, beam current from microamperes to kiloamperes, beam current density up to about 100 A/cm2, pulse duration from nanoseconds to dc, and electron energy from several keV to hundreds of keV. Applications include electron beam melting and welding, surface treatment, plasma chemistry, radiation technologies, laser pumping, microwave generation, and more.

  5. High-density matter: current status and future challenges

    Science.gov (United States)

    Stone, J. R.

    2015-05-01

    There are many fascinating processes in the Universe which we observe in more and more in detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in the core-collapse supernova explosion, the one of the most violent events in the Universe. As the result, the densest objects in the Universe, neutron stars and/or black holes are created. Naturally, the physical basis of these events should be understood in line with observation. The current status of our knowledge of processes in the life of stars is far from adequate for their true understanding. We show that although many models have been constructed their detailed ability to describe observations is limited or non-existent. Furthermore the general failure of all models means that we cannot tell which are heading in the right direction. A possible way forward in modeling of high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC). This model has a natural explanation for the saturation of nuclear forces and depends on very few adjustable parameters, strongly constrained by the underlying physics. Latest QMC results for compact objects and finite nuclei are presented.

  6. Vibration effect on magnetization and critical current density of superconductors

    Science.gov (United States)

    Golovchanskiy, Igor A.; Pan, Alexey V.; George, Jonathan; Wells, Frederick S.; Fedoseev, Sergey A.; Rozenfeld, Anatoly

    2016-07-01

    In this work the effect of vibrations on critical current density (J c ) of superconductors has been studied. The vibrations are shown to affect J c of all types of superconductors during their measurements, employing a vibrating sample magnetometer (VSM). Increasing vibration frequency (f) and/or amplitude (A) leads to progressive reduction of J c as a function of magnetic field (B a ). The effect of vibrations is substantially stronger in thin films. It leads to development of unexpected kinks on {J}c({B}a) curves. Analysis of magnetization loops and relaxation of magnetization in YBCO films revealed that the vibration effect can be treated as the effective reduction of pinning potential. The asymmetry of the vibration effect in ascending and descending B a is observed, indicating differences in free energy of the corresponding vortex structures. Thermal effects induced by vibrations with large f and A are shown to have rather insignificant influence, while the vibrational vortex dynamics exhibit a strong impact. The irreversibility field ({B}{{irr}}) is shown to be instrumentally defined, and its value depends on VSM settings. In addition, the practical importance of {B}{{irr}} for J c modeling is demonstrated.

  7. High-density matter: current status and future challenges

    Directory of Open Access Journals (Sweden)

    Stone J. R.

    2015-01-01

    Full Text Available There are many fascinating processes in the Universe which we observe in more and more in detail thanks to increasingly sophisticated technology. One of the most interesting phenomena is the life cycle of stars, their birth, evolution and death. If the stars are massive enough, they end their lives in the core-collapse supernova explosion, the one of the most violent events in the Universe. As the result, the densest objects in the Universe, neutron stars and/or black holes are created. Naturally, the physical basis of these events should be understood in line with observation. The current status of our knowledge of processes in the life of stars is far from adequate for their true understanding. We show that although many models have been constructed their detailed ability to describe observations is limited or non-existent. Furthermore the general failure of all models means that we cannot tell which are heading in the right direction. A possible way forward in modeling of high-density matter is outlined, exemplified by the quark-meson-coupling model (QMC. This model has a natural explanation for the saturation of nuclear forces and depends on very few adjustable parameters, strongly constrained by the underlying physics. Latest QMC results for compact objects and finite nuclei are presented.

  8. Fractional-space law for the neutron current density

    International Nuclear Information System (INIS)

    Highlights: ► The fractional-space law for the neutron current density is investigated. ► The fractional-space neutron balance equation is derived with fractional law. ► The fractional exponent was related with neutronic signals of APRM in BWRs. ► The Forsmark and Laguna Verde Nuclear Power Plant were analyzed. ► The results show that the fractional exponent is between 0.1881 and 0.9399. - Abstract: In this work, a fractional constitutive law (FCL) for the average neutron motion in nuclear reactors is presented. The FCL has a fractional exponent of the differential operator, which is the new unknown. The application of the FCL in the neutron balance equation leads to the fractional diffusion equation. The fractional exponent was evaluated using detrended fluctuation analysis (DFA). The DFA technique is based on the random walk theory and was applied to a power signal of the Forsmark Boiling Water Nuclear Reactor. The results show that the fractional exponent is between 0.1881 and 0.9399 for stationary operation, load changes and unstable conditions

  9. Plasma processes inside dispenser hollow cathodes

    Science.gov (United States)

    Mikellides, Ioannis G.; Katz, Ira; Goebel, Dan M.; Polk, James E.; Jameson, Kristina K.

    2006-06-01

    A two-dimensional fluid model of the plasma and neutral gas inside dispenser orificed hollow cathodes has been developed to quantify plasma processes that ultimately determine the life of the porous emitters inserted in these devices. The model self-consistently accounts for electron emission from the insert as well as for electron and ion flux losses from the plasma. Two cathodes, which are distinctively different in size and operating conditions, have been simulated numerically. It is found that the larger cathode, with outer tube diameter of 1.5cm and orifice diameter of 0.3cm, establishes an effective emission zone that spans approximately the full length of the emitter when operated at a discharge current of 25A and a flow rate of 5.5sccm. The net heating of the emitter is caused by ions that are produced by ionization of the neutral gas inside the tube and are then accelerated by the sheath along the emitter. The smaller cathode, with an outer diameter of 0.635cm and an orifice diameter of 0.1cm, does not exhibit the same operational characteristics. At a flow rate of 4.25sccm and discharge current of 12A, the smaller cathode requires 4.5 times the current density near the orifice and operates with more than 6 times the neutral particle density compared to the large cathode. As a result, the plasma particle density is almost one order of magnitude higher compared to the large cathode. The plasma density in this small cathode is high enough such that the Debye length is sufficiently small to allow "sheath funneling" into the pores of the emitter. By accessing areas deeper into the insert material, it is postulated that the overall emission of electrons is significantly enhanced. The maximum emission current density is found to be about 1A/mm2 in the small cathode, which is about one order of magnitude higher than attained in the large cathode. The effective emission zone in the small cathode extends to about 15% of the emitter length only, and the power

  10. Plasma processes inside dispenser hollow cathodes

    International Nuclear Information System (INIS)

    A two-dimensional fluid model of the plasma and neutral gas inside dispenser orificed hollow cathodes has been developed to quantify plasma processes that ultimately determine the life of the porous emitters inserted in these devices. The model self-consistently accounts for electron emission from the insert as well as for electron and ion flux losses from the plasma. Two cathodes, which are distinctively different in size and operating conditions, have been simulated numerically. It is found that the larger cathode, with outer tube diameter of 1.5 cm and orifice diameter of 0.3 cm, establishes an effective emission zone that spans approximately the full length of the emitter when operated at a discharge current of 25 A and a flow rate of 5.5 sccm. The net heating of the emitter is caused by ions that are produced by ionization of the neutral gas inside the tube and are then accelerated by the sheath along the emitter. The smaller cathode, with an outer diameter of 0.635 cm and an orifice diameter of 0.1 cm, does not exhibit the same operational characteristics. At a flow rate of 4.25 sccm and discharge current of 12 A, the smaller cathode requires 4.5 times the current density near the orifice and operates with more than 6 times the neutral particle density compared to the large cathode. As a result, the plasma particle density is almost one order of magnitude higher compared to the large cathode. The plasma density in this small cathode is high enough such that the Debye length is sufficiently small to allow 'sheath funneling' into the pores of the emitter. By accessing areas deeper into the insert material, it is postulated that the overall emission of electrons is significantly enhanced. The maximum emission current density is found to be about 1 A/mm2 in the small cathode, which is about one order of magnitude higher than attained in the large cathode. The effective emission zone in the small cathode extends to about 15% of the emitter length only, and the

  11. Synthesis and characterization of high-density LiFePO4/C composites as cathode materials for lithium-ion batteries

    International Nuclear Information System (INIS)

    To achieve a high-energy-density lithium electrode, high-density LiFePO4/C composite cathode material for a lithium-ion battery was synthesized using self-produced high-density FePO4 as a precursor, glucose as a C source, and Li2CO3 as a Li source, in a pipe furnace under an atmosphere of 5% H2-95% N2. The structure of the synthesized material was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical properties of the synthesized LiFePO4/carbon composite were investigated by cyclic voltammetry (CV) and the charge/discharge process. The tap-density of the synthesized LiFePO4/carbon composite powder with a carbon content of 7% reached 1.80 g m-3. The charge/discharge tests show that the cathode material has initial charge/discharge capacities of 190.5 and 167.0 mAh g-1, respectively, with a volume capacity of 300.6 mAh cm-3, at a 0.1C rate. At a rate of 5C, the LiFePO4/carbon composite shows a high discharge capacity of 98.3 mAh g-1 and a volume capacity of 176.94 mAh cm-3.

  12. Why palladium cathodes can bear resistance to methanol but not platinum cathodes

    International Nuclear Information System (INIS)

    Methanol crossover on the cathodes causes significant performance loss in direct methanol fuel cells, and the parasitic current induced by the electrochemical oxidation of methanol on the cathodes is believed to be the cause. Palladium cathodes are known to bear resistance to methanol but not platinum cathodes. By means of the density functional theory (DFT), the distorted molecular structure of the adsorbed methanol on platinum was revealed, and this distorted molecular structure indicates that platinum makes methanol has a tendency toward the elimination of the first hydrogen (involved in the first step of electrochemical oxidation of methanol) in electric neutrality, and loss of an electron can reinforce this tendency. However, palladium cannot distort the molecular structure of the adsorbed methanol, even in the loss of electron condition. The activation energies and the reaction energies calculated by means of DFT also show that after losing an electron, the elimination of the first hydrogen on platinum is more kinetically and thermodynamically favourable than that on palladium. These computational results can explain the experimental findings that no parasitic current is induced at palladium cathodes, but not at platinum cathodes; therefore, palladium cathodes have a methanol-resistance property

  13. Research and Development of a New Field Enhanced Low Temperature Thermionic Cathode that Enables Fluorescent Dimming and Loan Shedding without Auxiliary Cathode Heating

    Energy Technology Data Exchange (ETDEWEB)

    Feng Jin

    2009-01-07

    This is the final report for project entitled 'Research and development of a new field enhanced low temperature thermionic cathode that enables fluorescent dimming and load shedding without auxiliary cathode heating', under Agreement Number: DE-FC26-04NT-42329. Under this project, a highly efficient CNT based thermionic cathode was demonstrated. This cathode is capable of emitting electron at a current density two order of magnitude stronger then a typical fluorescent cathode at same temperatures, or capable of emitting at same current density but at temperature about 300 C lower than that of a fluorescent cathode. Detailed fabrication techniques were developed including CVD growth of CNTs and sputter deposition of oxide thin films on CNTs. These are mature technologies that have been widely used in industry for large scale materials processing and device fabrications, thus, with further development work, the techniques developed in this project can be scaled-up in manufacturing environment. The prototype cathodes developed in this project were tested in lighting plasma discharge environment. In many cases, they not only lit and sustain the plasma, but also out perform the fluorescent cathodes in key parameters such like cathode fall voltages. More work will be needed to further evaluate more detailed and longer term performance of the prototype cathode in lighting plasma.

  14. Nonuniqueness and derivative discontinuities in density-functional theories for current-carrying and superconducting systems

    OpenAIRE

    Capelle, K.; Vignale, G.

    2001-01-01

    Current-carrying and superconducting systems can be treated within density-functional theory if suitable additional density variables (the current density and the superconducting order parameter, respectively) are included in the density-functional formalism. Here we show that the corresponding conjugate potentials (vector and pair potentials, respectively) are {\\it not} uniquely determined by the densities. The Hohenberg-Kohn theorem of these generalized density-functional theories is thus w...

  15. Neuromodulation of conditioned placebo/nocebo in heat pain: anodal vs cathodal transcranial direct current stimulation to the right dorsolateral prefrontal cortex.

    Science.gov (United States)

    Egorova, Natalia; Yu, Rongjun; Kaur, Navneet; Vangel, Mark; Gollub, Randy L; Dougherty, Darin D; Kong, Jian; Camprodon, Joan A

    2015-07-01

    Placebo and nocebo play an important role in clinical practice and medical research. Modulating placebo/nocebo responses using noninvasive brain stimulation methods, such as transcranial direct current stimulation (tDCS), has the potential to harness these effects to therapeutic benefit in a clinical setting. In this study, we assessed the effect of anodal and cathodal tDCS over the right dorsolateral prefrontal cortex (rDLPFC) on conditioned placebo/nocebo cue response to heat pain. Two matched groups of healthy volunteers were subjected to an identical session of conditioning, during which low and high cues (abstract images) were associated with low and high pain levels, respectively. Twenty-minute 2-mA tDCS (either anodal or cathodal) over the rDLPFC was applied. The influence of tDCS current polarity (anodal vs cathodal) on placebo and nocebo was assessed, using subjects' pain ratings in response to identical pain preceded by the conditioned high or low cues. The duration of cue presentation varied to allow either fully conscious or subliminal processing. Significant placebo and nocebo effects in the anodal but not the cathodal group were elicited with the conditioning paradigm. This study provides evidence of a possibility to modulate the conditioned placebo and nocebo effect by changing the excitability of the rDLPFC using tDCS. PMID:25806605

  16. Emission from ferroelectric cathodes

    International Nuclear Information System (INIS)

    The authors have recently initiated an investigation of electron emission from ferroelectric cathodes. The experimental apparatus consisted of an electron diode and a 250 kV, 12 ohm, 70 ns pulsed high voltage power source. A planar triode modulator driven by a synthesized waveform generator initiates the polarization inversion and allows inversion pulse tailoring. The pulsed high voltage power source is capable of delivering two high voltage pulses within 50 μs of each other and is capable of operating at a sustained repetition rate of 5 Hz. The initial measurements indicate that emission current densities above the Child-Langmuir Space Charge Limit, JCL, are possible. They explain this effect to be based on a non-zero initial energy of the emitted electrons. They also determined that this effect is strongly coupled to relative timing between the inversion pulse and application of the main anode-cathode pulse. They also have initiated brightness measurements of the emitted beam and estimate a preliminary lower bound to be on the order of 109 A/m2-rad2 for currents close to JCL and factor of two less at currents over 4JCL. As in previous measurements at this Laboratory, they performed the measurement using a pepper pot technique. Beamlet profiles are recorded with a fast phosphor and gated cameras. They describe their apparatus and preliminary measurements

  17. Temperature variation of a thermionic cathode during electron emission

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    It is necessary to know the actual temperature of a thermionic cathode that works as the electron source in a microwave tube. It has been found that the temperature of the cathode drops markedly during the thermionic emission. For example, the temperature could fall by about 30oC under a current density of 2.92 A/cm2. Using the molecular thermodynamics, the dependence of the cathode temperature on the emission current density has been obtained. It has been theoretically pointed out that several factors, such as heating model and temperature coefficient of resis-tance of heater, can influence the cathode temperature. These theoretical conclu-sions were supported by the experimental results.

  18. Development of alloy-film coated dispenser cathode for terahertz vacuum electron devices application

    International Nuclear Information System (INIS)

    High power terahertz vacuum electron devices demand high current density and uniform emission dispenser cathode. It was found that the coating of noble metals e.g., Os, Ir, and Re on the surface of tungsten dispenser cathodes enhances the emission capabilities and uniformity. Hence metal coated cathode might be the best candidate for terahertz devices applications. In this study, ternary-alloy-film cathode (2Os:2Re:1 W) and Os coated cathode have been developed and the results are presented. The cathodes made out of this alloy coating showed 1.5 times higher emission and 0.02 eV emission uniformity as compared to those of simply Os coated cathodes which can be used in terahertz devices application.

  19. Development of alloy-film coated dispenser cathode for terahertz vacuum electron devices application

    Science.gov (United States)

    Barik, R. K.; Bera, A.; Raju, R. S.; Tanwar, A. K.; Baek, I. K.; Min, S. H.; Kwon, O. J.; Sattorov, M. A.; Lee, K. W.; Park, G.-S.

    2013-07-01

    High power terahertz vacuum electron devices demand high current density and uniform emission dispenser cathode. It was found that the coating of noble metals e.g., Os, Ir, and Re on the surface of tungsten dispenser cathodes enhances the emission capabilities and uniformity. Hence metal coated cathode might be the best candidate for terahertz devices applications. In this study, ternary-alloy-film cathode (2Os:2Re:1 W) and Os coated cathode have been developed and the results are presented. The cathodes made out of this alloy coating showed 1.5 times higher emission and 0.02 eV emission uniformity as compared to those of simply Os coated cathodes which can be used in terahertz devices application.

  20. Emission and surface characteristic of ternary alloy Ir/Re/W-coated impregnated tungsten cathodes

    Science.gov (United States)

    Zhang, Honglai; Liu, Yanwen; Zhang, Mingchen; Li, Yutao

    2005-09-01

    In order to improve the activation characteristics and emission ability of the conventional Ir-coated impregnated tungsten cathodes, a new type of dispenser cathode with ternary alloy Ir/Re/W coating was developed. The improved cathodes show higher emission current density and faster activation characteristics than that of the conventional pure Ir-coated impregnated tungsten cathodes. X-ray photoelectron spectroscopy (XPS) was used to analyze the element compositions on the surface of the cathodes coated with pure Ir and Ir/Re/W alloy. The results show that for pure Ir coating cathode, binary alloy (Ir/W) is formed. The surface atom concentration is near 50/50 after full activation. For ternary alloy coating cathode, the surface atom concentration has changed from 35%Ir-25%Re-40%W to 33%Ir-19%Re-48%W before and after activation.

  1. Emission and surface characteristic of ternary alloy Ir/Re/W-coated impregnated tungsten cathodes

    International Nuclear Information System (INIS)

    In order to improve the activation characteristics and emission ability of the conventional Ir-coated impregnated tungsten cathodes, a new type of dispenser cathode with ternary alloy Ir/Re/W coating was developed. The improved cathodes show higher emission current density and faster activation characteristics than that of the conventional pure Ir-coated impregnated tungsten cathodes. X-ray photoelectron spectroscopy (XPS) was used to analyze the element compositions on the surface of the cathodes coated with pure Ir and Ir/Re/W alloy. The results show that for pure Ir coating cathode, binary alloy (Ir/W) is formed. The surface atom concentration is near 50/50 after full activation. For ternary alloy coating cathode, the surface atom concentration has changed from 35%Ir-25%Re-40%W to 33%Ir-19%Re-48%W before and after activation

  2. Operation of an ungated diamond field-emission array cathode in a L-band radiofrequency electron source

    Energy Technology Data Exchange (ETDEWEB)

    Piot, P. [Northern Illinois Center for Accelerator and Detector Development and Department of Physics, Northern Illinois University, DeKalb, Illinois 60115 (United States); Accelerator Physics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States); Brau, C. A.; Gabella, W. E.; Ivanov, B.; Mendenhall, M. H. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Choi, B. K. [Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235 (United States); Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235 (United States); Blomberg, B.; Mihalcea, D.; Panuganti, H. [Northern Illinois Center for Accelerator and Detector Development and Department of Physics, Northern Illinois University, DeKalb, Illinois 60115 (United States); Jarvis, J. [Advanced Energy Systems, Inc., Medford, New York 11763 (United States); Prieto, P.; Reid, J. [Accelerator Division, Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States)

    2014-06-30

    We report on the operation of a field-emitter-array cathode in a conventional L-band radio-frequency electron source. The cathode consisted of an array of ∼10{sup 6} diamond tips on pyramids. Maximum current on the order of 15 mA was reached and the cathode did not show appreciable signs of fatigue after weeks of operation. The measured Fowler-Nordheim characteristics, transverse beam density, and current stability are discussed.

  3. Impact of the Usage of a Slotted Cathode Carbon Block on Thermoelectric Field in an Aluminum Reduction Cell

    Science.gov (United States)

    Tao, Wenju; Li, Tuofu; Wang, Zhaowen; Gao, Bingliang; Shi, Zhongning; Hu, Xianwei; Cui, Jianzhong

    2015-05-01

    The horizontal current in a metal pad of an aluminum reduction cell is critical because of its effect on the fluctuation of the metal pad. In this study, a novel cathode with a slotted cathode carbon block was proposed to decrease the horizontal current. The effects of the slotted cathode carbon block on the horizontal and vertical currents in the metal pad, cathode voltage, and temperature distribution in the cathode were calculated using the finite-element method. The results show that the slotted cathode carbon has great potential to decrease the horizontal current. When the length of slot b equals 400 mm, the maximum horizontal current density decreased by 50.4%. However, the cathode voltage in the cathode with the slotted cathode carbon was ~43 mV higher than that in a conventional cell, and the temperature in the slotted cathode carbon was slightly higher than that in a conventional carbon cell. Moreover, with increasing length of slot b, the maximum horizontal and vertical currents in the metal pad moved toward the cell center. The result of this study may provide the database in understanding the effect of the slotted cathode carbon on cell.

  4. Hollow Cathode With Multiple Radial Orifices

    Science.gov (United States)

    Brophy, John R.

    1992-01-01

    Improved hollow cathode serving as source of electrons has multiple radial orifices instead of single axial orifice. Distributes ion current more smoothly, over larger area. Prototype of high-current cathodes for ion engines in spacecraft. On Earth, cathodes used in large-diameter ion sources for industrial processing of materials. Radial orientation of orifices in new design causes current to be dispersed radially in vicinity of cathode. Advantageous where desireable to produce plasma more nearly uniform over wider region around cathode.

  5. Emission nonuniformity due to profilimetry variation in thermionic cathodes

    Science.gov (United States)

    Jensen, Kevin L.; Lau, Y. Y.; Jordan, Nicholas

    2006-04-01

    A model is developed which shows that the micron-scale ridges, introduced by the surface machining of thermionic dispenser cathodes, may lead to significant angular variations in the macroscopic current density on ring-shaped cathodes commonly used in gyrotrons. An account of the local enhancement in the microscopic emission current density on the ridges is considered for a representative physical model, which shows that the angular variation in current may be pronounced and accounted for by variations in ridges as a consequence of large scale profilimetry variations resulting from machining.

  6. Collisional Quenching of N2(A3Σu+) by Xylene and Current Prevention Phenomenon caused by Attaching By-product of Xylene on Cathode Surface

    Science.gov (United States)

    Suzuki, Susumu; Itoh, Haruo

    The collisional quenching rate coefficient of metastable nitrogen molecules N2(A3Σu+) by m-xylene (C8H10) is determined experimentally in the Townsend discharge. The diffusion coefficient of N2(A3Σu+), and the reflection coefficient of N2(A3Σu+) at the electrode surface are also determined simultaneously. During the experiment, we find that it is difficult to continue the current measurement necessary to determine the fundamental constants of N2(A3Σu+) for long period. It is considered that any by-product of xylene would be decomposed by N2(A3Σu+) is deposited on the cathode, through repeated experiments, then the current-voltage curves consistently shift to the higher-E/p0 region. For the purpose of clarifying the reason behind this behavior, we confirm that these changes are caused by the current prevention by the decreases of initial photoemission current from the cathode and the decrease in the secondary ionization coefficient γ, because the cathode surface is covered by deposition film of a by-product of decomposed xylene.

  7. Investigation of Endurance Performance of Carbon Nanotube Cathodes

    Science.gov (United States)

    Saito, Nanako; Yamagiwa, Yoshiki; Ohkawa, Yasushi; Nishida, Shin-Ichiro; Kitamura, Shoji

    The Aerospace Research and Development Directorate of the Japan Aerospace Exploration Agency (JAXA) is considering a demonstration of electrodynamic tether (EDT) systems in low Earth orbit (LEO). Carbon nanotubes (CNTs) have some advantages as electron sources compared to conventional Spindt type emitters, and so are expected to be useful in EDT systems. Experiments to investigate the durability of CNT cathodes in a space environment had been conducted in a diode mode, but it was found that electron extraction tests, in which the cathode with a gate electrode is used, are necessary to evaluate the endurance of CNTs more accurately. In this paper, we conducted long duration operating tests of a cathode with a gate. It was found that there was almost no change in cathode performance at current densities below 100 A/m2 even after the cathode was operated for over 500 hours in the high vacuum environment.

  8. Barium depletion study on impregnated cathodes and lifetime prediction

    Science.gov (United States)

    Roquais, J. M.; Poret, F.; le Doze, R.; Ricaud, J. L.; Monterrin, A.; Steinbrunn, A.

    2003-06-01

    In the thermionic cathodes used in cathode ray-tubes (CRTs), barium is the key element for the electronic emission. In the case of the dispenser cathodes made of a porous tungsten pellet impregnated with Ba, Ca aluminates, the evaporation of Ba determines the cathode lifetime with respect to emission performance in the CRT. The Ba evaporation results in progressive depletion of the impregnating material inside the pellet. In the present work, the Ba depletion with time has been extensively characterized over a large range of cathode temperature. Calculations using the depletion data allowed modeling of the depletion as a function of key parameters. The link between measured depletion and emission in tubes has been established, from which an end-of-life criterion was deduced. Taking modeling into account, predicting accelerated life-tests were performed using high-density maximum emission current (MIK).

  9. Barium depletion study on impregnated cathodes and lifetime prediction

    International Nuclear Information System (INIS)

    In the thermionic cathodes used in cathode ray-tubes (CRTs), barium is the key element for the electronic emission. In the case of the dispenser cathodes made of a porous tungsten pellet impregnated with Ba, Ca aluminates, the evaporation of Ba determines the cathode lifetime with respect to emission performance in the CRT. The Ba evaporation results in progressive depletion of the impregnating material inside the pellet. In the present work, the Ba depletion with time has been extensively characterized over a large range of cathode temperature. Calculations using the depletion data allowed modeling of the depletion as a function of key parameters. The link between measured depletion and emission in tubes has been established, from which an end-of-life criterion was deduced. Taking modeling into account, predicting accelerated life-tests were performed using high-density maximum emission current (MIK)

  10. Design of Cathode Heater Assembly for High Power Gyrotron

    Science.gov (United States)

    Bhattacharya, Ranajoy; Khatun, Hasina; Singh, Narendra Kr.; Singh, Udaybir; Sinha, A. K.

    2013-04-01

    A 3D model of dispenser cathode with toroid shape heater assembly is simulated using simulation software, ANSYS Multi-physics. The reported design study of cathode heater assembly of 1 MW 120 GHz gyrotron helps to optimize the input heater power with respect to cathode surface temperature. The simulation study shows that the input power depends strongly on the heater dimension as well as material properties including the potting material. The optimum input power helps to achieve desired current density (10 A/cm2) and cathode surface temperature (1000 °C). Further, the thermal and structural analyses are carried out to study the temperature distribution on the cathode assembly due to the heat dissipation and mechanical strength of the assembly.

  11. New doped tungsten cathodes. Applications to power grid tubes

    International Nuclear Information System (INIS)

    Thermionic emission behavior of tungsten/tungsten carbide modified with rare earth (La, Ce, Y) oxides is examined on account of suitability to deliver important current densities in a thermo-emissive set up and for long lifetime. Work functions of potential cathodes have been determined from Richardson plots for La2O3 doped tungsten and for tungsten covered with variable compositions rare earth tungstates. The role of platinum layers covering the cathode was also examined. Given all cathodes containing mainly lanthanum oxides were good emitters, emphasis was put on service lifetime. Comparisons of lifetime in tungsten doped with rare earth oxides and with rare earth tungstates show that microstructure of the operating cathodes may play the major role in the research of very long lifetime cathodes. Based on these results, tests still running show lifetime compatible with power grid tubes applications. (author)

  12. Generation of super-size macroparticles in a direct current vacuum arc discharge from a Mo-Cu cathode

    Science.gov (United States)

    Zhirkov, Igor; Petruhins, Andrejs; Polcik, Peter; Kolozsvári, Szilard; Rosen, Johanna

    2016-02-01

    An inherent property of cathodic arc is the generation of macroparticles, of a typical size ranging from submicrometer up to a few tens of μm. In this work, we have studied macroparticle generation from a Mo0.78Cu0.22 cathode used in a dc vacuum arc discharge, and we present evidence for super-size macroparticles of up to 0.7 mm in diameter. All analyzed particles are found to be rich in Mo (≥98 at. %). The particle generation is studied by visual observation of the cathode surface during arcing, by analysis of composition and geometrical features of the used cathode surface, and by examination of the generated macroparticles with respect to shape and composition. A mechanism for super-size macroparticle generation is suggested based on observed segregated layers of Mo and Cu identified in the topmost part of the cathode surface, likely due to the discrepancy in melting and evaporation temperatures of Mo and Cu. The results are of importance for increasing the fundamental understanding of macroparticle generation, which in turn may lead to increased process control and potentially provide paths for tuning, or even mitigating, macroparticle generation.

  13. Three Dimensional Effects on Virtual Cathode Formation in Electron Guns.

    Science.gov (United States)

    Valfells, Agust

    2001-10-01

    Recent experiments at the University of Maryland using photoemission from a dispenser cathode have yielded some interesting results regarding the effects of the area of emission and of the ratio between the pulse length and the gap transit time on the amount of current that may be drawn from an electron gun before a virtual cathode forms. The experiments show that a much higher current density may be drawn from a short pulse or limited emitter area than is anticipated by the Child-Langmuir limiting current. There is also evidence that the current may be increased even after virtual cathode formation, which leads one to distinguish between a limiting current density and a current density critical for virtual cathode formation. The experiments have also yielded some interesting results on the longitudinal structure of the current pulse passed through the anode. Some empirical and theoretical scaling laws regarding the formation of virtual cathodes in an electron gun will be presented. This work was motivated by the needs of the University of Maryland Electron Ring (UMER), where we wish to generate pulses that are well-localized in time and space.

  14. 小电流下真空电弧阴极斑点实验研究%Experimental research on vacuum arc cathode spots in small current

    Institute of Scientific and Technical Information of China (English)

    徐国顺; 吴国林; 庄劲武; 武瑾

    2015-01-01

    A cathode spots research platform which was based on vacuum arcing chamber was con‐structed ,the contacts material was CuCr50 ,the maximum distance was 4 .5 mm .Through high‐speed camera on the cathode spots ,a lot of small current vacuum arc cathode spots observation experiments were performed . Analysis found that cathode spots usually consist of multiple micro spots , these spots stay together and form a micro‐spot group .The current range of a single micro spot is from 7 A to 25 A .The upper limit current of a single cathode spot is 100 A .Along with the increase of current , the division of the micro‐spot group will be more and more obvious ,and eventually evolve into two in‐dependent cathode spots .%构建了基于可拆卸真空灭弧室的真空电弧阴极斑点研究平台,触头材料为CuCr50,极间最大开距4.5 mm .在极间无磁场影响的情况下,通过高速摄像机对阴极斑点进行拍摄,进行了大量小电流下阴极斑点的观测实验.结果发现:阴极斑点通常由多个微斑点组成,这些微斑点聚集在一起,形成一个微斑点群;单个微斑点的维持通流范围为7~25 A ;单个阴极斑点的通流上限为100 A ;随着电流的增大,单个阴极斑点会出现越来越明显的分裂现象,最终演变为两个相互独立的阴极斑点.

  15. Characterization and performance of a high-power all-solid-state drive laser for application in high-current photo-cathode injectors

    International Nuclear Information System (INIS)

    This paper describes the characterization and performance of a diode-pumped, high-power, picosecond laser system designed for high-current photo-cathode accelerator injectors at repetition rates of both 74.85 MHz and 748.5 MHz. A comprehensive set of measurements and analyses are presented for the amplifier gain, thermally induced beam size variation, pulse width, harmonic conversion efficiency, beam quality, power stability, beam pointing stability, and timing jitter. This laser demonstrates excellent overall system performance.

  16. The use of hollow cathodes in deposition processes: A critical review

    International Nuclear Information System (INIS)

    The first report of a discharge in a hollow cathode was by F. Paschen in 1916. That study showed that such a system was capable of producing a high electron flux and relatively low ion and neutral temperatures. About 40 years later, the work of Lidsky and others showed that hollow cathode arc discharges were one of the best plasma sources available at that time. The term “hollow cathode discharges” has commonly been used in reference to almost any discharge in a cathode with a cavity-like geometry, such that the plasma was enclosed or partially bound by the electrode walls that were at the cathode potential. Just as the magnetic field trapping of the electrons in a magnetron cathode results in an increase in the plasma density, in the hollow cathode, the reduced electron loss due to the geometry of the cathode also results in a higher plasma density. At least three types of discharge can be established in a hollow cathode. At low power and/or at relatively low gas pressures, the plasma is a “conventional” discharge characterized by low currents and medium to high voltages (we will call this a discharge in a hollow cathode or D-HC). Even this type of plasma has a higher density than a normal planar parallel-plate or magnetron system because the hollow geometry strongly reduces the loss of electrons. Using an adequate combination of gas pressure and applied power with a given hollow cathode diameter, or separation of the cathode surface, the negative glow of the plasma can expand to occupy the majority of the interior volume of the cathode. Under this condition the plasma current can, for the same voltage, be 100 to 1000 times the value of the “simple” D-HC discharge, and the plasma density is correspondingly larger (we call this a hollow cathode discharge or HCD). If the cathode is not cooled, the discharge can transform into a dispersed arc as the electrode temperature increases and thermal-field electron emission becomes an important additional source

  17. Rep-rate explosive whisker emission cathode investigations

    Science.gov (United States)

    Litz, Marc S.; Golden, Jeffry

    1994-05-01

    An experiment is underway to study the performance of several materials as field-emission cathodes for low voltage (EQ 100 kV), repetitive (coatings, niobium wire nanocomposite, and poly-crystalline tungsten. Surface emission is monitored by an array of Faraday cups. The `turn-on' time, uniformity of emission, and gap closure time are measured as a function of the spatially averaged, macroscopic electric field at the cathode. The carbon fiber cathode produces the largest current density and has the lowest threshold voltage for emission.

  18. Comparison of exact-exchange calculations for solids in current-spin-density- and spin-density-functional theory

    DEFF Research Database (Denmark)

    Sharma, S.; Pittalis, S.; Kurth, S.;

    2007-01-01

    The relative merits of current-spin-density- and spin-density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co, and...

  19. Theoretical Modeling of Internal Hydraulic Jump in Density Currents

    CERN Document Server

    Firoozabadi, Bahar; Aryanfar, Asghar; Afshin, Hossein

    2013-01-01

    In this paper, we propose an analytical framework for internal hydraulic jumps. Density jumps or internal hydraulic jumps occur when a supper critical flow of water discharges into a stagnant layer of water with slightly different density. The approach used here is control volume method which is also used to analyze ordinary hydraulic jumps. The important difference here is that entrainment is taken into account. Using conservation equations with the aid of some simplifying assumptions we come to an equation that gives jump downstream height as function of jump upstream characteristics and the entrainment. To determine the magnitude of downstream height we use an experimental equation for calculating the entrainment. Finally we verify our framework by comparing the height that we gain from the derived equation with some experimental data.

  20. Experimental Investigation of Thruster Cathode Physics

    Science.gov (United States)

    Crofton, Mark

    2004-11-01

    Advanced ion propulsion technologies are being developed under the Nuclear Electric Xenon Ion System (NEXIS) program for use in outer planet exploration. A revolutionary approach to thruster cathode design is dictated by the very high lifetime and propellant throughput requirements for nuclear electric applications. In conventional dispenser hollow cathodes used in thrusters, processes leading to depletion, inadequate transport, or insufficient production of barium are among those limiting the lifetime. A reservoir hollow cathode is being developed to address each of these failure mechanisms, exploiting four design variables - matrix material, source material, geometry, and thermal design - to essentially eliminate established failure modes. The very long anticipated lifetime necessitates new life validation methods to augment or replace the conventional lifetest approach. One important tool for quickly evaluating design changes is the ability to measure barium density inside a hollow cathode and/or in the plume. The dependence of barium density on temperature and other factors is an extremely important indicator of cathode health, particularly if the ratio Ba:BaO is also obtained. Comparison of barium production for reservoir and conventional cathodes will enable an assessment of the efficacy of reservoir designs and the goal of reducing barium consumption at a given emission current level. This study describes benchmark measurements made on a conventional cathode previously operated in a 20-kW NEXIS laboratory engine. Data on cathode operation and life-limiting processes were obtained through direct, real-time monitoring of atoms and molecules. A high-resolution, tunable laser system was employed to detect absorption of the low-density barium atoms inside the cathode. The plume was monitored also, using a quadrupole mass spectrometer to monitor multiple species and measure ion charge ratios. Data obtained with retarding potential analyzers or other means are

  1. DISCONTINUOUS FLOW OF TURBID DENSITY CURRENTS I. CHANNEL EXPANSION AND CONTRACTION

    Institute of Scientific and Technical Information of China (English)

    Jiahua FAN

    2005-01-01

    Laboratory experiments on turbid density currents were conducted to observe the flow features of these currents with abrupt contracted and expanded reaches. Experimental data were used to determine water entrainment coefficients for both channel expansion and contraction. Expressions for turbid density currents with water entrainment coefficients in abrupt contracted and expanded reaches were derived,and compared with experimental data.

  2. Cr-poisoning of a LaNi{sub 0.6}Fe{sub 0.4}O{sub 3} cathode under current load

    Energy Technology Data Exchange (ETDEWEB)

    Stodolny, M.K.; Van Berkel, F.P.F. [Energy Research Centre of the Netherlands ECN, Unit Hydrogen and Clean Fossil Fuels, P.O. Box 1, 1755 ZG, Petten (Netherlands); Boukamp, B.A.; Blank, D.H.A. [Department of Science and Technology and MESA Institute for Nanotechnology, University of Twente, 7500 AE, Enschede (Netherlands)

    2012-07-15

    This study demonstrates the significant impact of Cr-poisoning on the performance of the LaNi{sub 0.6}Fe{sub 0.4}O{sub 3} (LNF) SOFC cathode under current load. Volatile Cr-species, originating from a porous metallic foam, enter the working electrode and modify both the LNF cathode layer and the Gd{sub 0.4}Ce{sub 0.6}O{sub 1.8} (GDC) barrier layer, causing increasing overpotential and cell impedance. The increase of the ohmic resistance is caused by a decrease of the in-plane electronic conductivity of the LNF layer (due to Cr incorporation and Ni removal from the LNF perovskite lattice) combined with a deterioration of the ionic conductivity of the GDC barrier layer due to reactivity with Cr resulting in formation of a GdCrO{sub 3}-phase. The increase of the polarisation resistance is caused by a decrease of the electrochemical activity of the LNF surface towards oxygen reduction reaction at the triple phase boundary (TPB) due to Cr-incorporation in the outer shell of the LNF grains. Chemical reaction and electrochemically driven reaction of volatile Cr-species with LNF and GDC contributes to the extrinsic degradation of the LNF cathodes under current load.

  3. Fiske steps in Josephson junctions with alternating critical current density

    International Nuclear Information System (INIS)

    We have developed a simple model, in the framework of the Kulik theory of Fiske steps in Josephson junctions, for the electromagnetic resonances observed in the current voltage characteristics of certain high temperature superconductor grain boundary junctions. Some preliminary results are illustrated

  4. Density functional theory insights into the structural stability and Li diffusion properties of monoclinic and orthorhombic Li2FeSiO4 cathodes

    Science.gov (United States)

    Lu, Xia; Chiu, Hsien-Chieh; Bevan, Kirk H.; Jiang, De-Tong; Zaghib, Karim; Demopoulos, George P.

    2016-06-01

    Lithium iron orthosilicate (Li2FeSiO4) is an important alternative cathode for next generation Li-ion batteries due to its high theoretical capacity (330 mA h/g). However, its development has faced great challenges arising from significant structural complexity, including the disordered arrangement/orientation of Fe/Si tetrahedra, polytypes and its poorly understood Li storage and transport properties. In this context, ab-initio calculations are employed to investigate the phase stability and Li diffusion profiles of both monoclinic (P21) and orthorhombic (Pmn21) Li2FeSiO4 orthosilicates. The calculations demonstrate that formation of Lisbnd Fe antisites can induce a metastability competition between both phases, with neither dominating across nearly the entire discharging profile from Li2FeSiO4 through to LiFeSiO4. Furthermore, structural instability is shown to be a serious concern at discharge concentrations below LiFeSiO4 (1 Li extraction) due to the shared occupation of Li donated electrons with oxygen 2p orbitals - rather than the hypothesized transition to a tetravalent Fe4+ state. This finding is further supported by diffusion calculations that have determined a high activation energy barrier towards fast charging and rapid phase transitions. In summary, these theoretical results provide critical and timely insight into the structural dynamics of lithium iron orthosilicate, in pursuit of high energy density cathodes.

  5. Surface electron–hydronium ion-pair bound to silver and gold cathodes: A density functional theoretical study of photocatalytic hydrogen evolution reaction

    International Nuclear Information System (INIS)

    Noble metal catalysts, such as silver and gold, play a significant role in photocatalytic water splitting to hydrogen for their high efficiency and environmentally-friendly nature. In this paper, a surface electron–hydronium ion-pair (EHIP) was proposed as an intermediate for photocatalytic hydrogen evolution reaction (HER) on silver and gold cathodes based on density functional theory (DFT) calculations. The EHIP is in the configuration of H3O+(H2O)ne−, where the hydronium H3O+ and the electron is separated by water layers. The electron bound in the EHIP can first be excited under light irradiation, subsequently inducing a structural relaxation into a hydrated hydrogen atom. Eventually, two hydrogen atoms recombine into a hydrogen molecule in the thin layer close to the electrode surface, e.g. at the outer Helmholtz plane (OHP). Additionally, Raman spectra of the interfacial EHIP species are calculated, which is in support of the presence of EHIP intermediates in the process of photocatalytic HER on silver and gold cathodes

  6. Pore geometry of dispenser cathode surface vs. emission characteristics, and Ba recovery characteristics after ion bombardment

    Science.gov (United States)

    Higuchi, Toshiharu; Nakamura, Osamu; Matsumoto, Sadao; Uda, Eiichirou

    1999-05-01

    A study was conducted to investigate the emission characteristics and barium recovery characteristics after ion bombardment of two types of Ir-coated dispenser cathodes having a pore density on the surface layer of the cathodes of 4×10 4 and 1.3×10 4 pores/mm 2. Cathode current was measured under pulse operation in a range of 0.1-9% duty cycle. When the duty cycle dependence of emissions was examined, the current densities of both cathodes were the same in the case of 0.1% duty cycle, delivering about 12 A/cm 2. The work functions also showed the same value. However, evaluations of 4% duty cycle and 9% duty cycle found that the cathode with a higher pore density showed emission characteristics higher by 50% and 70%. Regarding the recovery time of barium and oxygen after argon ion bombardment with Auger electron spectroscopy (AES), the low-pore-density cathode required as long as 3 min for recovery, whereas the high-pore-density cathode recovered in 1.1 min. From the above experiments, it was clarified that emission characteristics under high duty and barium recovery characteristics after ion bombardment can be improved by increasing the pore density of the surface layer. The basic mechanisms leading to these results were also theoretically considered by solving surface diffusion equations.

  7. Plasma characterization on carbon fiber cathode by spectroscopic diagnostics

    International Nuclear Information System (INIS)

    This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide (CsI) coating powered by a ∼300 ns, ∼200 kV accelerating pulse. It was found that the CsI layers can not only improve the diode voltage, but also maintain a stable perveance. This indicates a slowly changed diode gap or a low cathode plasma expansion velocity. By spectroscopic diagnostics, in the vicinity of the cathode surface the average plasma density and temperature were found to be ∼3 × 1014 cm−3 and ∼5 eV, respectively, for an electron current density of ∼40 A/cm2. Furthermore, there exists a multicomponent plasma expansion toward the anode. The plasma expansion velocity, corresponding to the carbon and hydrogen ions, is estimated to be ∼1.5 cm/μs. Most notably, Cs spectroscopic line was obtained only at the distance ≤ 0.5 mm from the cathode surface. Carbon and hydrogen ions are obtained up to the distance of 2.5 mm from the cathode surface. Cs ions almost remain at the vicinity of the cathode surface. These results show that the addition of CsI enables a slow cathode plasma expansion toward the anode, providing a positive prospect for developing long-pulse electron beam sources. (general)

  8. Design, construction and long life endurance testing of cathode assemblies for use in microwave high-power transmitting tubes

    Science.gov (United States)

    Batra, R.; Marino, D.

    1986-01-01

    The cathode life test program sponsored by NASA Lewis Research Center at Watkins-Johnson Company has been in continuous operation since 1972. Its primary objective has been to evaluate the long life capability of barium dispenser cathodes to produce emission current densities of 2 A sq. cm. or more in an operational environment simulating that of a highpower microwave tube. The life test vehicles were equipped with convergent flow electron guns, drift space tubes with solenoid magnets for electron beam confinement and water-cooled depressed collectors. A variety of cathode types has been tested, including GE Tungstate, Litton Impregnated, Philips Type B and M, Semicon types S and M, and Spectra-Mat Type M. Recent emphasis has been on monitoring the performance of Philips Type M cathodes at 2 A sq. cm. and Sprectra-Mat and Semicon Type M cathodes at 4 A sq. cm. These cathodes have been operated at a constant current of 616 mA and a cathode anode voltage on the order of 10 kV. Cathode temperatures were maintained at 1010 C true as measured from black body holes in the backs of the cathodes. This report presents results of the cathode life test program from July l982 through April l986. The results include hours of operation and performance data in the form of normalized emission current density versus temperature curves (Miram plots).

  9. Density-Driven Currents and Deposition of Fine Materials

    DEFF Research Database (Denmark)

    Saremi, Sina

    . Dredging activities always make changes to the environment, such as alteration of the coastal or river morphology, currents and wave climates, and water quality. Such changes may be considered improving or degrading to the environment. The type of material being dredged, type of the dredging equipment and...... stages can be captured using a sediment budget approach, i.e., by using continuity equations for water and sediment phases. In the first part of this study, the compositional transformation and the bed height inside the hopper are obtained by solving these equations, considering monodisperse, bidisperse...... part of this study, a 3 dimensional two-phase mixture method has been used to model the detailed processes involved in the highly concentrated mixture inside the hopper. The benefit of such model is that it takes into account important dynamic interactions and volume exchange effects due to the...

  10. Electrospun FeS2@Carbon Fiber Electrode as a High Energy Density Cathode for Rechargeable Lithium Batteries.

    Science.gov (United States)

    Zhu, Yujie; Fan, Xiulin; Suo, Liumin; Luo, Chao; Gao, Tao; Wang, Chunsheng

    2016-01-26

    In this study, an FeS2@carbon fiber electrode is developed with FeS2 nanoparticles either embedded in or attached to carbon fibers by using an electrospinning method. By applying this binder-free, metal-current-collector-free FeS2@carbon fiber electrode, both the redox reaction and capacity decay mechanisms for the Li-FeS2 system are revealed by changing the electrolyte (conventional carbonate electrolyte and a "solvent-in-salt"-type Li-S battery electrolyte) and working voltage ranges (1.0-3.0 V and 1.5-3.0 V vs Li/Li(+)). The FeS2@carbon fiber electrode shows stable cycling performance in both the conventional carbonate electrolyte and the solvent-in-salt-type Li-S battery electrolyte in the voltage range of 1.5-3.0 V. Electrochemical tests in the solvent-in-salt-type Li-S battery electrolyte indicate that the Li-FeS2 system becomes a hybrid of the Li-S cell and Li-iron sulfide cell after the initial cycle. Based on the understanding on the capacity decay mechanisms, the cycling stability of the Li-FeS2 system in the voltage range of 1.0-3.0 V is then significantly enhanced by coating the FeS2@carbon fiber electrode with a thin layer of Al2O3. The Al2O3-coated electrode demonstrates excellent cycling performance with high discharge energy densities at both the material level (∼1300 Wh/kg-FeS2) and the electrode level (∼1000 Wh/kg-FeS2 electrode). PMID:26700975

  11. Reinvestigation of Distribution Regularity of Cathode Current in Hull Cell%对霍尔槽阴极电流分布规律的再研究

    Institute of Scientific and Technical Information of China (English)

    梅天庆

    2000-01-01

    With 16 types of electroplating baths and processes most commonly used in industry, including 3 Znplatings, 4 Cu, 5 Ni and 2 Sn platings as well as 2 Au imitation, current distribution regularities on cathode in Hullcell were reinvestigated by measuring c.d. of 20 small isolated cathode sections of cathode plate. The empirical for-mula describing regularity Dk = I (a - b lg L ) was examined and compared with results obtained from experiments.More exact values of slope a and intercept - b for different electroplating baths are provided.%采用最常用的16种电镀工艺,通过测量霍尔槽阴极片上被分割的20块小阴极条的平均电流密度,再次研究了霍尔槽阴极电流的分布规律。所研究的电镀工艺包括3种镀锌、4种镀铜、5种镀镍、2种镀锡以及2种仿金镀。考察了描述上述分布规律的经验公式Dk=I(a-blg L),并与所得实验结果进行比较,提出了不同电镀工艺的截矩a和斜率-b的更准确数值。

  12. Explosive emission cathode plasmas in intense relativistic electron beam diodes

    International Nuclear Information System (INIS)

    An experimental study of cathode plasmas in planar diodes driven by a Sandia Nereus accelerator (270 kV, 60 kA, 70 ns), with particular attention devoted to plasma uniformity and expansion velocity, has been carried out. This diode current density was varied over a factor of ten and the rate of rise of the applied field dE/dt was varied over a factor of six. Different cathode materials, coatings, and surface roughnesses were used and the effects of glow discharge cleaning and in situ heating of the cathode were examined. Framing photography, electron beam dosimetry, perveance measurements, optical interferometry, and (spatially and temporally resolved) spectroscopy were used to diagnose the plasma uniformity, electron beam uniformity, plasma front motion, electron density, plasma composition, motion of distinct species, electron temperature, and ion (and neutral) densities. Electron beam uniformity is seen to be related to cathode plasma uniformity; this uniformity is enhanced by a high value of (the microscopic) dE/dt, which is determined both by the rise time of the applied field and by the cathode surface roughness. The significance of dE/dt is believed to be related to the screening effect of emitted electrons. The motion of the plasma front is seen to be affected by two phenomena. To begin with, all species of the cathode plasma are seen to expand at the same rate. The ions are believed to be accelerated to velocities on the order of 2 to 3 cm/μs in dense cathode spot regions at the cathode surface. Plasma expansion is also influenced by electric pressure effects, which are determined by the shape of the driving power pulse. A simple cathode plasma model, which explains the similarity of plasmas in diodes with greatly differing parameters, is proposed. The relevance of these results to inductively driven diodes, repetitively pulsed diodes, and magnetically insulated transmission lines is also discussed

  13. Cathodic oxygen reduction catalyzed by bacteria in microbial fuel cells.

    Science.gov (United States)

    Rabaey, Korneel; Read, Suzanne T; Clauwaert, Peter; Freguia, Stefano; Bond, Philip L; Blackall, Linda L; Keller, Jurg

    2008-05-01

    Microbial fuel cells (MFCs) have the potential to combine wastewater treatment efficiency with energetic efficiency. One of the major impediments to MFC implementation is the operation of the cathode compartment, as it employs environmentally unfriendly catalysts such as platinum. As recently shown, bacteria can facilitate sustainable and cost-effective cathode catalysis for nitrate and also oxygen. Here we describe a carbon cathode open to the air, on which attached bacteria catalyzed oxygen reduction. The bacteria present were able to reduce oxygen as the ultimate electron acceptor using electrons provided by the solid-phase cathode. Current densities of up to 2.2 A m(-2) cathode projected surface were obtained (0.303+/-0.017 W m(-2), 15 W m(-3) total reactor volume). The cathodic microbial community was dominated by Sphingobacterium, Acinetobacter and Acidovorax sp., according to 16S rRNA gene clone library analysis. Isolates of Sphingobacterium sp. and Acinetobacter sp. were obtained using H(2)/O(2) mixtures. Some of the pure culture isolates obtained from the cathode showed an increase in the power output of up to three-fold compared to a non-inoculated control, that is, from 0.015+/-0.001 to 0.049+/-0.025 W m(-2) cathode projected surface. The strong decrease in activation losses indicates that bacteria function as true catalysts for oxygen reduction. Owing to the high overpotential for non-catalyzed reduction, oxygen is only to a limited extent competitive toward the electron donor, that is, the cathode. Further research to refine the operational parameters and increase the current density by modifying the electrode surface and elucidating the bacterial metabolism is warranted. PMID:18288216

  14. Phase dynamics of low critical current density YBCO Josephson junctions

    International Nuclear Information System (INIS)

    Highlights: • We study the phase dynamics of YBaCuO Josephson junctions using various tools. • We derive information on the dissipation in a wide range of transport parameters. • Dissipation in such devices can be described by a frequency dependent damping model. • The use of different substrates allows us to tune the shell circuit. - Abstract: High critical temperature superconductors (HTS) based devices can have impact in the study of the phase dynamics of Josephson junctions (JJs) thanks to the wide range of junction parameters they offer and to their unconventional properties. Measurements of current–voltage characteristics and of switching current distributions constitute a direct way to classify different regimes of the phase dynamics and of the transport, also in nontrivial case of the moderately damped regime (MDR). MDR is going to be more and more common in JJs with advances in nanopatterning superconductors and synthesizing novel hybrid systems. Distinctive signatures of macroscopic quantum tunneling and of thermal activation in presence of different tunable levels of dissipation have been detected in YBCO grain boundary JJs. Experimental data are supported by Monte Carlo simulations of the phase dynamics, in a wide range of temperatures and dissipation levels. This allows us to quantify dissipation in the MDR and partially reconstruct a phase diagram as guideline for a wide range of moderately damped systems

  15. High Current Density Beamlets from an RF Argon Source for Heavy Ion Fusion Applications

    International Nuclear Information System (INIS)

    In a new approach to develop high current beams for heavy ion fusion, beam current at about 0.5 ampere per channel can be obtained by merging an array of high current density beamlets of 5 mA each. We have done computer simulations to study the transport of high current density beamlets and the emittance growth due to this merging process. In our RF multicusp source experiment, we have produced a cluster of 61 beamlets using minimum gas flow. The current density from a 0.25 cm diameter aperture reached 100 mA/cm2. The normalized emittance of 0.02 π-mm-mrad corresponds to an equivalent ion temperature of 2.4 eV. These results showed that the RF argon plasma source is suitable for producing high current density beamlets that can be merged to form a high current high brightness beam for HIF application

  16. Cationic fluorinated polymer binders for microbial fuel cell cathodes

    KAUST Repository

    Chen, Guang

    2012-01-01

    Fluorinated quaternary ammonium-containing polymers were used as catalyst binders in microbial fuel cell (MFC) cathodes. The performance of the cathodes was examined and compared to NAFION ® and other sulfonated aromatic cathode catalyst binders using linear sweep voltammetry (LSV), impedance spectroscopy, and performance tests in single chamber air-cathode MFCs. The cathodes with quaternary ammonium functionalized fluorinated poly(arylene ether) (Q-FPAE) binders showed similar current density and charge transfer resistance (R ct) to cathodes with NAFION ® binders. Cathodes containing either of these fluorinated binders exhibited better electrochemical responses than cathodes with sulfonated or quaternary ammonium-functionalized RADEL ® poly(sulfone) (S-Radel or Q-Radel) binders. After 19 cycles (19 d), the power densities of all the MFCs declined compared to the initial cycles due to biofouling at the cathode. MFC cathodes with fluorinated polymer binders (1445 mW m -2, Q-FPAE-1.4-H; 1397 mW m -2, Q-FPAE-1.4-Cl; 1277 mW m -2, NAFION ®; and 1256 mW m -2, Q-FPAE-1.0-Cl) had better performance than those with non-fluorinated polymer binders (880 mW m -2, S-Radel; 670 mW m -2, Q-Radel). There was a 15% increase in the power density using the Q-FPAE binder with a 40% higher ion exchange capacity (Q-FPAE-1.4-H compared to Q-FPAE-1.0-Cl) after 19 cycles of operation, but there was no effect on the power production due to counter ions in the binder (Cl -vs. HCO 3 -). The highest-performance cathodes (NAFION ® and Q-FPAE binders) had the lowest charge transfer resistances (R ct) in fresh and in fouled cathodes despite the presence of thick biofilms on the surface of the electrodes. These results show that fluorinated binders may decrease the penetration of the biofilm and associated biopolymers into the cathode structure, which helps to combat MFC performance loss over time. © 2012 The Royal Society of Chemistry.

  17. Measurement of nonuniform current densities and current kinetics in Aplysia neurons using a large patch method.

    OpenAIRE

    Johnson, J W; Thompson, S.

    1989-01-01

    A large patch electrode was used to measure local currents from the cell bodies of Aplysia neurons that were voltage-clamped by a two-microelectrode method. Patch currents recorded at the soma cap, antipodal to the origin of the axon, and whole-cell currents were recorded simultaneously and normalized to membrane capacitance. The patch electrode could be reused and moved to different locations which allowed currents from adjacent patches on a single cell to be compared. The results show that ...

  18. Near-surface Density Currents Observed in the Southeast Pacific Stratocumulus-topped Marine Boundary Layer

    Energy Technology Data Exchange (ETDEWEB)

    Wilbanks, Matt C.; Yuter, S. E.; de Szoeke, S.; Brewer, W. A.; Miller, Matthew A.; Hall, Andrew M.; Burleyson, Casey D.

    2015-09-01

    Density currents (i.e. cold pools or outflows) beneath marine stratocumulus clouds are characterized using a 30-d data set of ship-based observations obtained during the 2008 Variability of American Monsoon Systems (VAMOS) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in the southeast Pacific. An objective method identifies 71 density current fronts using an air density criterion and isolates each density current’s core (peak density) and tail (dissipating) zone. Compared to front and core zones, most density current tails exhibited weaker density gradients and wind anomalies elongated about the axis of the mean wind. The mean cloud-level advection relative to the surface layer wind (1.9 m s-1) nearly matches the mean density current propagation speed (1.8 m s-1). The similarity in speeds allows drizzle cells to deposit tails in their wakes. Based on high-resolution scanning Doppler lidar data, prefrontal updrafts had a mean intensity of 0.91 m s-1, reached an average altitude of 800 m, and were often surmounted by low-lying shelf clouds not connected to the overlying stratocumulus cloud. Nearly 90% of density currents were identified when C-band radar estimated 30-km diameter areal average rain rates exceeded 1 mm d-1. Rather than peaking when rain rates are highest overnight, density current occurrence peaks between 0600 and 0800 local solar time when enhanced local drizzle co-occurs with shallow subcloud dry and stable layers. The dry layers may contribute to density current formation by enhancing subcloud evaporation of drizzle. Density currents preferentially occur in regions of open cells but also occur in regions of closed cells.

  19. Variation of Eddy Current Density Distribution and its Effect on Crack Signal in Eddy Current Non-Destructive of Testing

    Directory of Open Access Journals (Sweden)

    Ladislav Janousek

    2006-01-01

    Full Text Available The paper deals with variation of eddy current density distribution along material depth and investigates an effect of the variation on a crack signal in eddy current non-destructive testing. Four coaxial rectangular tangential coils are used to induce eddy currents in a tested conductive object. The exciting coils are driven independently by phase-shifted AC currents; a ratio of amplitudes of the exciting currents is continuously changed to vary the distribution of eddy current density along material depth under a circular pick-up coil positioned in centre between the exciting coils. Dependences of a crack signal amplitude and its phase on the ratio are evaluated and special features are extracted. It is revealed that the dependences are strongly influenced by depth of a crack, and thus the extracted features can enhance evaluation of a detected crack.

  20. Inter-ELM evolution of the edge current density profile on the ASDEX Upgrade tokamak

    International Nuclear Information System (INIS)

    The sudden decrease of plasma stored energy and subsequent power deposition on the first wall of a tokamak device due to edge localised modes (ELMs) is potentially detrimental to the success of a future fusion reactor. Understanding and control of ELMs is critical for the longevity of these devices and also to maximise their performance. The commonly accepted picture of ELMs posits a critical pressure gradient and current density in the plasma edge, above which coupled magnetohydrodynamic (MHD) peeling-ballooning modes are driven unstable. Much analysis has been presented in recent years on the spatial and temporal evolution of the edge pressure gradient. However, the edge current density has typically been overlooked due to the difficulties in measuring this quantity. In this thesis, a novel method of current density recovery is presented, using the equilibrium solver CLISTE to reconstruct a high resolution equilibrium utilising both external magnetic and internal edge kinetic data measured on the ASDEX Upgrade (AUG) tokamak. The evolution of the edge current density relative to an ELM crash is presented, showing that a resistive delay in the buildup of the current density is unlikely. An uncertainty analysis shows that the edge current density can be determined with an accuracy consistent with that of the kinetic data used. A comparison with neoclassical theory demonstrates excellent agreement between the current density determined by CLISTE and the calculated profiles. Three ELM mitigation regimes are investigated: Type-II ELMs, ELMs suppressed by external magnetic perturbations (MPs), and Nitrogen seeded ELMs. In the first two cases, the current density is found to decrease as mitigation onsets, indicating a more ballooning-like plasma behaviour. In the latter case, the flux surface averaged current density can decrease while the local current density increases, thus providing a mechanism to suppress both the peeling and ballooning modes.

  1. An improved pulse-line accelerator-driven, intense current-density, and high-brightness pseudospark electron beam

    International Nuclear Information System (INIS)

    A high-voltage (200 kV), high current-density, low-emittance (23 π·mm mrd), high-brightness (8 x 1010 A/(mrd)2) electron beam was generated in a pseudospark chamber filled with 15 Pa nitrogen and driven by a modified pulse line accelerator. The beam ejected with ≤1-mm diameter, 2.2-kA beam current, 400-ns pulse length, and about 20 cm propagation distance. Exposure of 10 shots on the same film produced a hole of 1.6-mm diameter at 7 cm downstream of the anode, and showed its good reproducibility. After 60 shots, it was observed that almost no destructive damage traces were left on the surfaces of the various electrodes and insulators of the pseudospark discharge chamber. It was experimentally found that the quality of the pseudospark electron beam remains very high, even at high voltages (of several hundred kilovolts), similar to low voltages, and is much better than the quality of the cold-cathode electron beams

  2. Thermionic properties of Mo-La2O3 cathode wires

    Institute of Scientific and Technical Information of China (English)

    张久兴; 周美玲; 周文元; 王金淑; 聂祚仁; 左铁镛

    2002-01-01

    The recent advances in Mo-La2O3 thermionic cathode materials were presented. It is shown that Mo-La2O3 cathode has better ductility, radioactive pollution-free, excellent thermionic electron-emission properties and lower operating temperature compared with W-ThO2 cathode. At operating temperature 1350~1400℃, the average saturation current of the Mo-La2O3 cathode is 118mA, the corresponding average current density is 367mA/cm2, and the average emission efficiency is 11.8mA/W. The lifetime of diode is more than 2000h when the stable emission current is 80mA. Moreover, the lifetime of practical 6T51-type triode is more than 1000h. These advances show that the Mo-La2O3 cathode electron tube is closer to industry application.

  3. Observation of Lower-Hybrid Current Drive at High Densities in the Alcator C Tokamak

    Science.gov (United States)

    Porkolab, M.; Schuss, J. J.; Lloyd, B.; Takase, Y.; Texter, S.; Bonoli, P.; Fiore, C.; Gandy, R.; Gwinn, D.; Lipschultz, B.; Marmar, E.; Pappas, D.; Parker, R.; Pribyl, P.

    1984-07-01

    A quasi-steady-state lower-hybrid current-drive operation is demonstrated in the Alcator C tokamak at densities up to n―e~=1×1014 cm-3. The current-drive efficiency is measured experimentally over a wide range of densities and magnetic fields. The radial distribution of high-energy x rays indicates that the current-carrying electrons peak near the plasma axis.

  4. Theoretical model and experimental investigation of current density boundary condition for welding arc study

    OpenAIRE

    Boutaghane, A.; Bouhadef, K.; Valensi, F.; Pellerin, S.; Benkedda, Y.

    2011-01-01

    Abstract This paper presents results of theoretical and experimental investigation of the welding arc in Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) processes. A theoretical model consisting in simultaneous resolution of the set of conservation equations for mass, momentum, energy and current, Ohm's law and Maxwell equation is used to predict temperatures and current density distribution in argon welding arcs. A current density profile h...

  5. Finite temperature bosonic charge and current densities in compactified cosmic string spacetime

    CERN Document Server

    Mohammadi, Azadeh

    2015-01-01

    In this paper we study the expectation values of the induced charge and current densities for a massive bosonic field with nonzero chemical potential in the geometry of a higher dimensional compactified cosmic string with magnetic fluxes, along the string core and also enclosed by the compactified direction, in thermal equilibrium at finite temperature $T$. These densities are calculated by decomposing them into the vacuum expectation values and finite temperature contributions coming from the particles and antiparticles. The only nonzero components correspond to the charge, azimuthal and axial current densities. By using the Abel-Plana formula, we decompose the components of the densities into the part induced by the cosmic string and the one by the compactification. The charge density is an odd function of the chemical potential and even periodic function of the magnetic flux with a period equal to the quantum flux. Moreover, the azimuthal (axial) current density is an even function of the chemical potentia...

  6. Finite temperature fermionic charge and current densities induced by a cosmic string with magnetic flux

    CERN Document Server

    Mohammadi, A; Saharian, A A

    2014-01-01

    We investigate the finite temperature expectation values of the charge and current densities for a massive fermionic field with nonzero chemical potential, $\\mu$, in the geometry of a straight cosmic string with a magnetic flux running along its axis. These densities are decomposed into the vacuum expectation values and contributions coming from the particles and antiparticles. The charge density is an even periodic function of the magnetic flux with the period equal to the quantum flux and an odd function of the chemical potential. The only nonzero component of the current density corresponds to the azimuthal current. The latter is an odd periodic function of the magnetic flux and an even function of the chemical potential. At high temperatures, the parts in the charge density and azimuthal current induced by the planar angle deficit and magnetic flux are exponentially small. The asymptotic behavior at low temperatures crucially depends whether the value $|\\mu|$ is larger or smaller than the mass of the fiel...

  7. Current density and conductivity through modified gravity in the graphene with defects

    CERN Document Server

    Sepehri, Alireza; Bamba, Kazuharu; Capozziello, Salvatore; Saridakis, Emmanuel N

    2016-01-01

    We propose a model describing the evolution of the free electron current density in graphene. Based on the concept of Mp-branes, we perform the analysis using the difference between curvatures of parallel and antiparallel spins. In such a framework an effective graviton emerges in the form of gauge field exchange between electrons. In a plain graphene system, the curvatures produced by both kinds of spins neutralize each other. However, in the presence of defects, the inequality between curvatures leads to the emergence of current density, modified gravity and conductivity. Depending on the type of the defects, the resulting current density can be negative or positive.

  8. Estimation of current density distribution of PAFC by analysis of cell exhaust gas

    Energy Technology Data Exchange (ETDEWEB)

    Kato, S.; Seya, A. [Fuji Electric Co., Ltd., Ichihara-shi (Japan); Asano, A. [Fuji Electric Corporate, Ltd., Yokosuka-shi (Japan)

    1996-12-31

    To estimate distributions of Current densities, voltages, gas concentrations, etc., in phosphoric acid fuel cell (PAFC) stacks, is very important for getting fuel cells with higher quality. In this work, we leave developed a numerical simulation tool to map out the distribution in a PAFC stack. And especially to Study Current density distribution in the reaction area of the cell, we analyzed gas composition in several positions inside a gas outlet manifold of the PAFC stack. Comparing these measured data with calculated data, the current density distribution in a cell plane calculated by the simulation, was certified.

  9. Effects of Electron Flow Current Density on Flow Impedance of Magnetically Insulated Transmission Lines

    Institute of Scientific and Technical Information of China (English)

    HE Yong; ZOU Wen-Kang; SONG Sheng-Yi

    2011-01-01

    @@ In modern pulsed power systems, magnetically insulated transmission lines (MITLs) are used to couple power between the driver and the load.The circuit parameters of MITLs are well understood by employing the concept of Sow impedance derived from Maxwell's equations and pressure balance across the flow.However, the electron density in an MITL is always taken as constant in the application of flow impedance.Thus effects of electron flow current density (product of electron density and drift velocity) in an MITL are neglected.We calculate the flow impedances of an MITL and compare them under three classical MITL theories, in which the electron density profile and electron flow current density are different from each other.It is found that the assumption of constant electron density profile in the calculation of the Sow impedance is not always valid.The electron density profile and the electron flow current density have significant effects on flow impedance of the MITL.The details of the electron flow current density and its effects on the operation impedance of the MITL should be addressed more explicitly experiments and theories in the future.

  10. Transimssion and compression of an intense relativistic electron beam produced by a converging annular diode with return current feedback through the cathode. Part II. The experiments

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, J.G.; Schuch, R.L.

    1976-02-01

    The complete results of the experiments with the converging annular diode within return current feedback through the cathode (Triax) are reported herein. The diode was designed to focus a relativistic high-current electron beam to a small focus. It did confirm the Triaxial theory detailed in Part I, and it did achieve a factor of 10 areal compression with 50% efficiency (which was below expectations). There were two principal reasons for this shortfall. First, the rapid diode plasma motion of 10 cm/..mu..sec that was discovered necessitated the use of larger A-K gaps than expected and led to thicker beam sheets than are needed for good focusing. Second, the intrinsic angular spread of the electrons, even from the best cathode surfaces, introduced excessive angular momentum into the beam so that only a minor portion of the electrons could reach the axis. However, the yield of useful information about diode physics in general and about the influence of prepulse, the role of diode plasmas, the motion of energetic beams within conducting boundaries, diode emission properties, and diode diagnostic techniques in particle has had a significant and useful impact on the electron beam program at Sandia.

  11. Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors

    OpenAIRE

    Jain, Akshay; Aravindan, Vanchiappan; Jayaraman, Sundaramurthy; Kumar, Palaniswamy Suresh; Balasubramanian, Rajasekhar; Ramakrishna, Seeram; Madhavi, Srinivasan; Srinivasan, M. P.

    2013-01-01

    In this manuscript, a dramatic increase in the energy density of ~ 69 Wh kg−1 and an extraordinary cycleability ~ 2000 cycles of the Li-ion hybrid electrochemical capacitors (Li-HEC) is achieved by employing tailored activated carbon (AC) of ~ 60% mesoporosity derived from coconut shells (CS). The AC is obtained by both physical and chemical hydrothermal carbonization activation process, and compared to the commercial AC powders (CAC) in terms of the supercapacitance performance in single ele...

  12. Current density profile and electron beam localization measurements using carbon pellets on T-10

    International Nuclear Information System (INIS)

    The letter presents experimental evidence and an analysis of two phenomena arising during carbon pellet ablation - a toroidal trajectory deflection and enhanced localized ablation in the electron cyclotron resonance (ECR) current drive regime. A model developed for describing the toroidal deflection of a carbon pellet in a tokamak shows that the trajectory curvature is sensitive to the current density. Photography of the pellet trajectory is used as a diagnostic for the determination of the local current density in an ohmically heated plasma. Directly measured current profiles using pellets are in reasonable agreement with that obtained using the Spitzer conductivity, and current density fluctuations have been observed that are probably associated with magnetic islands. It is shown that in the ECR current drive regime on T-10, energetic electrons probably stimulated by the microwave power are located in a narrow zone (2 cm thickness in the radial direction) with sharp boundaries. (author). Letter-to-the-editor. 7 refs, 5 figs

  13. LETTER: Current density profile and electron beam localization measurements using carbon pellets on T-10

    Science.gov (United States)

    Egorov, S. M.; Kuteev, B. V.; Miroshnikov, I. V.; Mikhailenko, A. A.; Sergeev, V. Yu.; Ushakov, S. N.; Bagdasarov, A. A.; Chistyakov, V. V.; Elizavetin, D. Yu.; Vasin, N. L.

    1992-11-01

    The authors present experimental evidence and an analysis of two phenomena arising during carbon pellet ablation-a toroidal trajectory deflection and enhanced localized ablation in the electron cyclotron resonance (ECR) current drive regime. A model developed for describing the toroidal deflection of a carbon pellet in a tokamak shows that the trajectory curvature is sensitive to the current density. Photography of the pellet trajectory is used as a diagnostic for the determination of the local current density in an ohmically heated plasma. Directly measured current profiles using pellets are in reasonable agreement with that obtained using the Spitzer conductivity, and current density fluctuations have been observed that are probably associated with magnetic islands. It is shown that in the ECR current drive regime on T-10, energetic electrons probably stimulated by the microwave power are located in a narrow zone (2 cm thickness in the radial direction) with sharp boundaries

  14. Erosion behaviour of a Ti3SiC2 cathode under low-current vacuum arc

    International Nuclear Information System (INIS)

    In this article, the arc erosion behaviour of high-purity Ti3SiC2 in vacuum was investigated by x-ray diffraction, scanning electron microscope, energy dispersive x-ray spectroscopy, and micro-Raman spectroscopy. From the results obtained, Ti3SiC2 is unstable due to the high energy intensity and high temperature of the vacuum arc. The dissociation of Ti3SiC2 takes place at the sample surface, resulting in the formation of solid TiCx and gaseous Si. TiCx is ejected from cathode to the surface of anode while Si is evaporated to the vacuum chamber. The micro-Raman results reveal that small amounts of carbon appeared as a by-product of the dissociation of Ti3SiC2, indicating that the Ti–C bonding is broken down under the vacuum arc. (paper)

  15. Cathode and interdigitated air distributor geometry optimization in polymer electrolyte membrane (PEM) fuel cells

    International Nuclear Information System (INIS)

    A steady-state single-phase three-dimensional electro-chemical model is combined with a nonlinear constrained optimization procedure to maximize the performance of the cathode and the interdigitated air distributor in a polymer electrolyte membrane (PEM) fuel cell. The cathode and the interdigitated air distributor design parameters considered include: the cathode thickness, the thickness of the interdigitated air distributor channels and the width of the interdigitated air distributor channels. A statistical sensitivity analysis is used to determine robustness of the optimal PEM fuel cell design. The results of the optimization analysis show that higher current densities at the membrane/cathode interface are obtained in the PEM cathode and the interdigitated air distributor geometries that promote convective oxygen transport to the membrane/cathode interface and reduce the thickness of the boundary diffusion layer at the same interface. The statistical sensitivity analysis results show that, while the predicted average current density at the membrane/cathode interface is affected by uncertainties in a number of model parameters, the optimal designs of the PEM cathode and the interdigitated air distributor are quite robust

  16. The effect of current density on CNx crystal grain growth in electrochemical deposition

    International Nuclear Information System (INIS)

    The effect of charge current density on the growth of CNx films by electrolysis of a methanol-urea solution is investigated experimentally. It is seen that the c-C3N4 phase grains in the films are about 200-300 nm for a density of 55 mA/cm2 and dendrite growth takes place with grains as large as 7 μm formed when density is about 70 mA/cm2. (authors)

  17. Emission characteristics of Y1Ba2Cu3O7-δ cathode

    International Nuclear Information System (INIS)

    The results are presented of experimental investigation of the electron beam in diode with cathode on the base of Y1Ba2Cu3O7-δ. After corresponding cathode training, the cathode made from Y1Ba2Cu3O7-δ material may be practicable of stable current electron beam yeild. It is shown experimentally that the voltage of diode of about 100-300 kV there exists an evident possibility of forming the electron beams with the current density of 70 A-380 A/cm2. The motion velicity of cathode plasma in the direction of anode for this material of a cathode amounts to (1-3)x 106 cm/s

  18. Cold smoke: smoke-induced density currents cause unexpected smoke transport near large wildfires

    Directory of Open Access Journals (Sweden)

    N. P. Lareau

    2015-07-01

    Full Text Available First observations of smoke-induced density currents originating from large wildfires are presented. Using a novel mobile Doppler LiDAR and additional in situ measurements we document a deep (~ 2 km smoke-filled density current that propagates more than 25 km at speeds up to 4.5 m s−1 near a large forest fire in northern California. Based on these observations we show that the dynamics governing the spread of the smoke layer result from differential solar heating between the smoke-filled and smoke-free portions of the atmospheric boundary layer. A calculation of the theoretical density current speed agrees well with the observed propagation speed. Additional LiDAR and photographic documentation of other smoke-filled density currents demonstrate that these previously unknown phenomena are relatively common near large wildfires and can cause severe and unexpected smoke inundation of populated areas.

  19. A Galvanostatic Modeling for Preparation of Electrodeposited Nanocrystalline Coatings by Control of Current Density

    Institute of Scientific and Technical Information of China (English)

    Ali Mohammad Rashidi

    2012-01-01

    The correlation between the grain size of electrodeposited coatings and the current densities was modeled by considering galvanostatic conditions. In order to test the model by experimental results, nanocrystalline (NC) nickel samples were deposited at different current densities using a Watts bath. The grain size of the deposits was evaluated by X-ray diffraction (XRD) technique. Model predictions were validated by finding a curve being the best-fit to the experimental results which were gathered from literature for different NC coatings in addition to those data measured in this research for NC nickel coatings. According to our model, the variation of grain size with the reciprocal of the current density follows a power law. A good agreement between the experimental results and model predictions was observed which indicated that the derived analytical model is applicable for producting the nanocrystalline electrodeposits with the desired grain size by controling current density.

  20. Preparation and characterization of high-Tc superconducting thin films with high critical current densities

    International Nuclear Information System (INIS)

    The project was carried out in relation to possible cable and electronics applications of high-Tc materials. Laser ablation was used as the deposition technique because of its stoichiometry conservation. Films were made in the YBa2Cu3O7 compound due to its relatively simple stoichiometry compared to other High-Tc compounds. Much attention was paid to the critical current density. A very high critical current density was reached. By using texture analysis by X-ray diffraction, it was found that films with high critical current densities were epitaxial, while films with low critical current densities contained several crystalline orientations. Four techniques for patterning the films were used - photo lithography and wet etch, laser ablation lithography, laser writing and electron beam lithography and ion milling. Sub-micron patterning has been demonstrated without degradation of the superconducting properties. The achieved patterning resolution is sufficient for preparation of many superconducting components. (AB)

  1. Finite temperature bosonic charge and current densities in compactified cosmic string spacetime

    Science.gov (United States)

    Mohammadi, A.; Bezerra de Mello, E. R.

    2016-06-01

    In this paper, we study the expectation values of the induced charge and current densities for a massive bosonic field with nonzero chemical potential in the geometry of a higher-dimensional compactified cosmic string with magnetic fluxes along the string core and also enclosed by the compactified direction in thermal equilibrium at finite temperature T . These densities are calculated by decomposing them into the vacuum expectation values and finite temperature contributions coming from the particles and antiparticles. The only nonzero components correspond to the charge, azimuthal, and axial current densities. By using the Abel-Plana formula, we decompose the components of the densities into the part induced by the cosmic string and the one by the compactification. The charge density is an odd function of the chemical potential and even periodic function of the magnetic flux with a period equal to the quantum flux. Moreover, the azimuthal (axial) current density is an even function of the chemical potential and an odd (even) periodic function of the magnetic flux with the same period. In this paper, our main concern is the thermal effect on the charge and current densities, including some limiting cases, the low- and high-temperature approximations. We show that in all cases, the temperature enhances the induced densities.

  2. Cold Smoke: smoke-induced density currents cause unexpected smoke transport near large wildfires

    OpenAIRE

    N. P. Lareau; Clements, C. B.

    2015-01-01

    The first observations of smoke-induced density currents originating from large wildfires are presented. Using a novel mobile Doppler lidar and additional in situ measurements, we document a deep (~ 2 km) smoke-filled density current that propagates more than 25 km at speeds up to 4.5 m s−1 near a large forest fire in northern California. Based on these observations we show that the dynamics governing the spread of the smoke layer result from differential solar heating between ...

  3. Numerical Study on Density Residual Currents of the Bohai Sea in Summer

    Institute of Scientific and Technical Information of China (English)

    刘桂梅; 王辉; 孙松; 韩博平

    2003-01-01

    M2 tide and density residual currents in the Bohai Sea were examined using the Blumberg and Mellor 3D nonlinear numerical coastal circulation model incorporating Mellor and Yamada level 2.5 turbulent closure model. The tidal results showed good agreement with previous work. The model results indicated that the density residual currents are robust in summer; and that at the transition zone between well mixed and stratified water, the horizontal velocity is high and the vertical velocity is positive.

  4. Current density imaging sequence for monitoring current distribution during delivery of electric pulses in irreversible electroporation

    OpenAIRE

    Serša, Igor; Kranjc, Matej; Miklavčič, Damijan

    2015-01-01

    Background Electroporation is gaining its importance in everyday clinical practice of cancer treatment. For its success it is extremely important that coverage of the target tissue, i.e. treated tumor, with electric field is within the specified range. Therefore, an efficient tool for the electric field monitoring in the tumor during delivery of electroporation pulses is needed. The electric field can be reconstructed by the magnetic resonance electric impedance tomography method from current...

  5. Experimental study of the velocity of density currents in convergent and divergent channels

    Institute of Scientific and Technical Information of China (English)

    Hasan Torabi POUDEH; Samad EMAMGHOLIZADEH; Manoocher Fathi-MOGHADAM

    2014-01-01

    The head velocity of the density current in the convergent and divergent channel is a key parameter for evaluating the extent to which suspended material travels, and for determining the type and distribution of sediment in the water body. This study experimentally evaluated the effects of the reach degree of convergence and divergence on the head velocity of the density current. Experiments were conducted in the flume with 6.0 m long, 0.72 m width and 0.6 m height. The head velocity was measured at three convergent degrees (-8o;-12o;-26o), at three divergent degrees (8o; 12o; 26o) and two slopes (0.009, 0.016) for various discharges. The measured head velocity of the density current is compared with the head velocity of the density current in the constant cross section channel. Based on non-dimensional and statistical analysis, relations as linear multiple regression are offered for predicting head velocity of the density current in the convergent, divergent and constant cross section channel. Also the results of this research show that for the same slope and discharge, the head velocity of the density current in the convergent and divergent channel are greater and less than the head velocity of the constant cross section, respectively.

  6. Numerical Simulation of Current Density Distribution in Keyhole Double-Sided Arc Welding

    Institute of Scientific and Technical Information of China (English)

    Junsheng SUN; Chuansong WU; Min ZHANG; Houxiao WANG

    2004-01-01

    In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process.Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.

  7. Efficient reduction of CO2 to CO with high current density using in situ or ex situ prepared Bi-based materials.

    Science.gov (United States)

    Medina-Ramos, Jonnathan; DiMeglio, John L; Rosenthal, Joel

    2014-06-11

    The development of inexpensive electrocatalysts that can promote the reduction of CO2 to CO with high selectivity, efficiency, and large current densities is an important step on the path to renewable production of liquid carbon-based fuels. While precious metals such as gold and silver have historically been the most active cathode materials for CO2 reduction, the price of these materials precludes their use on the scale required for fuel production. Bismuth, by comparison, is an affordable and environmentally benign metal that shows promise for CO2 conversion applications. In this work, we show that a bismuth-carbon monoxide evolving catalyst (Bi-CMEC) can be formed under either aqueous or nonaqueous conditions using versatile electrodeposition methods. In situ formation of this thin-film catalyst on an inexpensive carbon electrode using an organic soluble Bi(3+) precursor streamlines preparation of this material and generates a robust catalyst for CO2 reduction. In the presence of appropriate imidazolium based ionic liquid promoters, the Bi-CMEC platform can selectively catalyze conversion of CO2 to CO without the need for a costly supporting electrolyte. This inexpensive system can catalyze evolution of CO with current densities as high as jCO = 25-30 mA/cm(2) and attendant energy efficiencies of ΦCO ≈ 80% for the cathodic half reaction. These metrics highlight the efficiency of Bi-CMEC, since only noble metals have been previously shown to promote this fuel forming half reaction with such high energy efficiency. Moreover, the rate of CO production by Bi-CMEC ranges from approximately 0.1-0.5 mmol·cm(-2)·h(-1) at an applied overpotential of η ≈ 250 mV for a cathode with surface area equal to 1.0 cm(2). This CO evolution activity is much higher than that afforded by other non-noble metal cathode materials and distinguishes Bi-CMEC as a superior and inexpensive platform for electrochemical conversion of CO2 to fuel. PMID:24783975

  8. Current density functional theory using meta-generalized gradient exchange-correlation functionals

    OpenAIRE

    Furness, James W.; Verbeke, Joachim; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M.

    2015-01-01

    We present the self-consistent implementation of current-dependent (hybrid) meta generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn--Sham current density-functional theory (KS-CDFT). A unique feature of the non-perturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 a.u. (...

  9. DARHT 2 kA Cathode Development

    International Nuclear Information System (INIS)

    In the campaign to achieve 2 kA of electron beam current, we have made several changes to the DARHT-II injector during 2006-2007. These changes resulted in a significant increase in the beam current, achieving the 2 kA milestone. Until recently (before 2007), the maximum beam current that was produced from the 6.5-inch diameter (612M) cathode was about 1300 A when the cathode was operating at a maximum temperature of 1140 C. At this temperature level, the heat loss was dominated by radiation which is proportional to temperature to the fourth power. The maximum operating temperature was limited by the damage threshold of the potted filament and the capacity of the filament heater power supply, as well as the shortening of the cathode life time. There were also signs of overheating at other components in the cathode assembly. Thus it was clear that our approach to increase beam current could not be simply trying to run at a higher temperature and the preferred way was to operate with a cathode that has a lower work function. The dispenser cathode initially used was the type 612M made by SpectraMat. According to the manufacturer's bulletin, this cathode should be able to produce more than 10 A/cm2 of current density (corresponding to 2 kA of total beam current) at our operating conditions. Instead the measured emission (space charge limited) was 6 A/cm2. The result was similar even after we had revised the activation and handling procedures to adhere more closely to the recommend steps (taking longer time and nonstop to do the out-gassing). Vacuum was a major concern in considering the cathode's performance. Although the vacuum gauges at the injector vessel indicated 10-8 Torr, the actual vacuum condition near the cathode in the central region of the vessel, where there might be significant out-gassing from the heater region, was never determined. Poor vacuum at the surface of the cathode degraded the emission (by raising the work function value). We reexamined all

  10. DARHT 2 kA Cathode Development

    Energy Technology Data Exchange (ETDEWEB)

    Henestroza, E.; Houck, T.; Kwan, J.W.; Leitner, M.; Miram, G.; Prichard, B.; Roy, P.K.; Waldron, W.; Westenskow, G.; Yu, S.; Bieniosek, F.M.

    2009-03-09

    In the campaign to achieve 2 kA of electron beam current, we have made several changes to the DARHT-II injector during 2006-2007. These changes resulted in a significant increase in the beam current, achieving the 2 kA milestone. Until recently (before 2007), the maximum beam current that was produced from the 6.5-inch diameter (612M) cathode was about 1300 A when the cathode was operating at a maximum temperature of 1140 C. At this temperature level, the heat loss was dominated by radiation which is proportional to temperature to the fourth power. The maximum operating temperature was limited by the damage threshold of the potted filament and the capacity of the filament heater power supply, as well as the shortening of the cathode life time. There were also signs of overheating at other components in the cathode assembly. Thus it was clear that our approach to increase beam current could not be simply trying to run at a higher temperature and the preferred way was to operate with a cathode that has a lower work function. The dispenser cathode initially used was the type 612M made by SpectraMat. According to the manufacturer's bulletin, this cathode should be able to produce more than 10 A/cm{sup 2} of current density (corresponding to 2 kA of total beam current) at our operating conditions. Instead the measured emission (space charge limited) was 6 A/cm{sup 2}. The result was similar even after we had revised the activation and handling procedures to adhere more closely to the recommend steps (taking longer time and nonstop to do the out-gassing). Vacuum was a major concern in considering the cathode's performance. Although the vacuum gauges at the injector vessel indicated 10{sup -8} Torr, the actual vacuum condition near the cathode in the central region of the vessel, where there might be significant out-gassing from the heater region, was never determined. Poor vacuum at the surface of the cathode degraded the emission (by raising the work function

  11. Generation of multiple toroidal dust vortices by a non-monotonic density gradient in a direct current glow discharge plasma

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, Manjit, E-mail: manjit@ipr.res.in; Bose, Sayak; Chattopadhyay, P. K.; Sharma, D.; Ghosh, J.; Saxena, Y. C. [Institute for Plasma Research, Gandhinagar 382428 (India); Thomas, Edward [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States)

    2015-09-15

    Observation of two well-separated dust vortices in an unmagnetized parallel plate DC glow discharge plasma is reported in this paper. A non-monotonic radial density profile, achieved by an especially designed cathode structure using a concentric metallic disk and ring of different radii, is observed to produce double dust tori between cathode and anode. PIV analysis of the still images of the double tori shows oppositely rotating dust structures between the central disk and the ring. Langmuir probe measurements of background plasma shows a non-uniform plasma density profile between the disk and the ring. Location and sense of rotation of the dust vortices coincides with the location and direction of the radial gradient in the ion drag force caused by the radial density gradient. The experimentally observed dust vorticity matches well with the calculated one using hydrodynamic formulations with shear in ion drag dominating over the dust charge gradient. These results corroborate that a radial gradient in the ion drag force directed towards cathode is the principal cause of dust rotation.

  12. Generation of multiple toroidal dust vortices by a non-monotonic density gradient in a direct current glow discharge plasma

    International Nuclear Information System (INIS)

    Observation of two well-separated dust vortices in an unmagnetized parallel plate DC glow discharge plasma is reported in this paper. A non-monotonic radial density profile, achieved by an especially designed cathode structure using a concentric metallic disk and ring of different radii, is observed to produce double dust tori between cathode and anode. PIV analysis of the still images of the double tori shows oppositely rotating dust structures between the central disk and the ring. Langmuir probe measurements of background plasma shows a non-uniform plasma density profile between the disk and the ring. Location and sense of rotation of the dust vortices coincides with the location and direction of the radial gradient in the ion drag force caused by the radial density gradient. The experimentally observed dust vorticity matches well with the calculated one using hydrodynamic formulations with shear in ion drag dominating over the dust charge gradient. These results corroborate that a radial gradient in the ion drag force directed towards cathode is the principal cause of dust rotation

  13. Microelectrochemical investigation of the effect of cathodic polarisation on the corrosion resistance of 304L stainless steel in a 1 M NaCl solution

    OpenAIRE

    Arjmand Gholenji, Farzin; Adriaens, Annemie

    2012-01-01

    304L stainless steel was cathodically polarised in a 1 M sodium chloride solution using a microcapillary electrochemical droplet cell. During the cathodic polarisation the produced hydrogen atoms penetrate into the sample and accumulate at sites of the steel surface. We observed that the pitting potential (E-pit), the anodic current density (I-corr) and the corrosion potential (E-corr) of the polarised steel are strongly influenced by the applied cathodic potential and therefore by the amount...

  14. A Critical Review of Published Data on the Gas Temperature and the Electron Density in the Electrolyte Cathode Atmospheric Glow Discharges

    Directory of Open Access Journals (Sweden)

    Tamás Cserfalvi

    2012-05-01

    Full Text Available Electrolyte Cathode Discharge (ELCAD spectrometry, a novel sensitive multielement direct analytical method for metal traces in aqueous solutions, was introduced in 1993 as a new sensing principle. Since then several works have tried to develop an operational mechanism for this exotic atmospheric glow plasma technique, however these attempts cannot be combined into a valid model description. In this review we summarize the conceptual and technical problems we found in this upcoming research field of direct sensors. The TG gas temperature and the ne electron density values published up to now for ELCAD are very confusing. These data were evaluated by three conditions. The first is the gas composition of the ELCAD plasma, since TG was determined from the emitted intensity of the N2 and OH bands. Secondly, since the ELCAD is an atmospheric glow discharge, thus, the obtained TG has to be close to the Te electron temperature. This can be used for the mutual validation of the received temperature data. Thirdly, as a consequence of the second condition, the values of TG and ne have to agree with the Engel-Brown approximation of the Saha-equation related to weakly ionized glow discharge plasmas. Application of non-adequate experimental methods and theoretical treatment leads to unreliable descriptions which cannot be used to optimize the detector performance.

  15. Applications of the exact-exchange functional in current density functional theory

    International Nuclear Information System (INIS)

    The proper description of many-electron systems in the presence of magnetic fields within density-functional theory (DFT) requires the current density to be used as basic variable besides the electron and magnetization densities. Applications of this current-DFT (CDFT) formalism have been limited because electron-gas-based approximations for the CDFT exchange-correlation functional have serious pathologies which make them awkward to use in practical calculations. As an alternative, we present a CDFT version of the optimized effective potential method which allows for the use of explicitly orbital-dependent functionals and which also provides a natural framework to treat non-collinear current and magnetization densities. Results obtained with the exact exchange functional are presented for the spurious energy splittings of degenerate ground states of open-shell atoms as well as for orbital magnetic moments and spin-orbit induced band-splittings in solids

  16. Finite temperature fermion condensate, charge and current densities in a (2+1)-dimensional conical space

    CERN Document Server

    Bellucci, S; Bragança, E; Saharian, A A

    2016-01-01

    We evaluate the fermion condensate and the expectation values of the charge and current densities for a massive fermionic field in (2+1)-dimensional conical spacetime with a magnetic flux located at the cone apex. The consideration is done for both irreducible representations of the Clifford algebra. The expectation values are decomposed into the vacuum expectation values and contributions coming from particles and antiparticles. All these contributions are periodic functions of the magnetic flux with the period equal to the flux quantum. Related to the non-invariance of the model under the parity and time-reversal transformations, the fermion condensate and the charge density have indefinite parity with respect to the change of the signs of the magnetic flux and chemical potential. The expectation value of the radial current density vanishes. The azimuthal current density is the same for both the irreducible representations of the Clifford algebra. It is an odd function of the magnetic flux and an even funct...

  17. Comparison of voltage-current characteristics of high quality Bi-2223 tapes with Hall-sensor measurements and computed current density distributions

    Energy Technology Data Exchange (ETDEWEB)

    Masti, Mika; Lehtonen, Jorma; Peraelae, Raine; Nah, Wansoo; Kang, Joonsun

    2004-01-15

    The critical current reduction caused by the self-field of the current is measurable on modern HTS tapes. The current density reduction is strongest near the tape edges due to tape geometry and strong anisotropy. In voltage (V)-current (I) measurement the self-field also increases with rising current. In this paper V(I) measurements are simulated with Finite Element Method to study the evolution of the current density distribution in increasing self-field. The computations are based on local magnetic flux density dependent current density-electric field characteristics, which have been derived from V(I) characteristics measured at external magnetic fields. Current densities determined with least squares method from measured magnetic flux density profiles are compared to the computed ones. The results show good correlation between the power law model calculations and measurements, but only with current amplitudes bigger than half of the critical current.

  18. Synchrotron Investigations of SOFC Cathode Degradation

    Energy Technology Data Exchange (ETDEWEB)

    Idzerda, Yves

    2013-09-30

    The atomic variations occurring in cathode/electrolyte interface regions of La{sub 1-x}Sr{sub x}Co{sub y}Fe{sub 1-y}O{sub 3-δ} (LSCF) cathodes and other SOFC related materials have been investigated and characterized using soft X-ray Absorption Spectroscopy (XAS) and diffuse soft X-ray Resonant Scattering (XRS). X-ray Absorption Spectroscopy in the soft X-ray region (soft XAS) is shown to be a sensitive technique to quantify the disruption that occurs and can be used to suggest a concrete mechanism for the degradation. For LSC, LSF, and LSCF films, a significant degradation mechanism is shown to be Sr out-diffusion. By using the XAS spectra of hexavalent Cr in SrCrO4 and trivalent Cr in Cr2O3, the driving factor for Sr segregation was identified to be the oxygen vacancy concentration at the anode and cathode side of of symmetric LSCF/GDC/LSCF heterostructures. This is direct evidence of vacancy induced cation diffusion and is shown to be a significant indicator of cathode/electrolyte interfacial degradation. X-ray absorption spectroscopy is used to identify the occupation of the A-sites and B-sites for LSC, LSF, and LSCF cathodes doped with other transition metals, including doping induced migration of Sr to the anti-site for Sr, a significant cathode degradation indicator. By using spatially resolved valence mapping of Co, a complete picture of the surface electrochemistry can be determined. This is especially important in identifying degradation phenomena where the degradation is spatially localized to the extremities of the electrochemistry and not the average. For samples that have electrochemical parameters that are measured to be spatially uniform, the Co valence modifications were correlated to the effects of current density, overpotential, and humidity.

  19. Effect of the current density on electrodepositing alpha-lead dioxide coating on aluminum substrate

    Institute of Scientific and Technical Information of China (English)

    Burning CHEN; Zhongcheng GUO; Hui HUANG; Xianwan YANG; Yuandong CAO

    2009-01-01

    The α-PbO_2 electrodes are prepared by anodic electrodeposition on Al/conductive coating electrode from alkaline plumbite solutions in order to investigate the effect of the different current densities on the properties of α-PbO_2 electrodes. The physic-ochemical properties of the α-PbO_2 electrodes are analyzed by using SEM, EDS, XRD, Tafel plot, linear sweep voltammetry (LSV) and A.C. Impedance. A compact and uniform layer of lead dioxide was obtained at the current density of 3 mA-cm~(-2) . A further increase in current density results in smaller particles with high porosity. EDS and XRD analyses have shown that the PbO_2 deposited in alkaline conditions is highly non stoichiometric, and the PbO impurities are formed on the surface layer besides the α-PbO_2. The corrosion resistance of α-PbO_2 at the low current density is superior to that of the high current density. It can be attributed to a porous layer of deposited films at high current densities. When used as anodes for oxygen evolution in aqueous Zn~(2+) 50 g·L~(-1), H_2SO_4 150 g·L~(-1), the Al/conductive coating/α-PbO_2 exhibits lower potential compared to Pb electrode. Al/conductive coating/α-PbO_2 electrode with the best electrocatalytic activity was obtained at current density of 1 mA·cm~(-2). The lowest roughness factor was obtained at 1 mA·cm~(-2).

  20. Measurement of local current density of all-vanadium redox flow batteries

    Science.gov (United States)

    Hsieh, Wen-Yen; Leu, Chih-Hsing; Wu, Chun-Hsing; Chen, Yong-Song

    2014-12-01

    This article presents a preliminary study of the measurement of local current density in all-vanadium redox flow batteries. Two batteries are designed and manufactured in this study, and the experimental results are compared. In the first cell, the current collector is divided into 25 segments, and the flow field plate is not segmented, whereas in the other cell, the flow field plate is segmented. The effects of the electrolyte flow rate on the battery efficiencies and the local current density variation are investigated. The experimental results show that the current density near the outlet significantly decreases when the discharge capacity approaches zero. In addition, the battery has a larger discharge depth at a higher electrolyte flow rate.

  1. Four-dimensional ultrasound current source density imaging of a dipole field

    OpenAIRE

    Z. H. Wang; Olafsson, R.; P Ingram; Q. Li; Qin, Y.; Witte, R. S.

    2011-01-01

    Ultrasound current source density imaging (UCSDI) potentially transforms conventional electrical mapping of excitable organs, such as the brain and heart. For this study, we demonstrate volume imaging of a time-varying current field by scanning a focused ultrasound beam and detecting the acoustoelectric (AE) interaction signal. A pair of electrodes produced an alternating current distribution in a special imaging chamber filled with a 0.9% NaCl solution. A pulsed 1 MHz ultrasound beam was sca...

  2. Microstructure and critical current density in high-Tc metal oxide superconductors

    International Nuclear Information System (INIS)

    Superconductor powders in the U-Ba-Cu-O (YBCO) and Bi-Pb-Sr-Ca-Cu-O (BSCCO) systems were synthesized by freeze-drying. Powders were characterized, and processed into samples for evaluation of superconducting behavior. Freeze-drying is attractive because the powders have high purity, are homogeneous, have a small size and are active. YBCO powders can be sintered to high density at 890 degrees C. Many compositions, processing approaches and heat treatments were explored in an effort to understand relations between microstructure and critical density, and to improve the critical current density. Powders were also formed into sputtering targets for coating preparation at Stanford University. The highest critical current density achieved with the YBCO powders was ∼15,000 A/cm2 at 4.2K and 0.5T using powders treated to prevent carbon contamination. The BSCCO materials with the highest critical current density, ∼30,000 A/cm2 at the same conditions were formed by heat treating melted and quenched samples. All critical current density measurements were made by Stanford University, a subcontractor to this effort. Stanford University also prepared coatings by off-axis magnetron sputtering

  3. Numerical simulation of transport of a high-current electron beam generated by the secondary-emission cathode gun in a decreasing solenoidal field

    International Nuclear Information System (INIS)

    The software tool has been developed for computing the electron beam formation by means of the secondary-emission cathode magnetron gun in the electron energy range between 30 and 65 keV at beam transport in a decreasing magnetic field of the solenoid. Numerical simulation data on the tubular electron flow motion and visualization are presented. The beam current was investigated versus the amplitude and gradient of the field decrease, and also, versus the initial beam particle distribution in the phase space. It has been found that for the given simulation conditions, the magnetic field reconfiguration has an effect only on the total displacement of the electron beam, without causing a noticeable change in the shape of the final flow distribution along the longitudinal coordinate

  4. Effect of A-site Non-stoichiometry on LSCF Cathodes

    Energy Technology Data Exchange (ETDEWEB)

    Templeton, Jared W.; Lu, Zigui; Stevenson, Jeffry W.; Hardy, John S.

    2011-09-01

    LSCF Cathodes were explored when effected with A-site non-stoichiometry. At 700-800 C, the operating temperatures of intermediate temperature (IT-) SOFCs have enabled the use of stainless steels in the SOFC framework and current collectors, allowing significant reductions in cost. However, the lower operating temperatures of IT-SOFC's also result in significant decreases in power densities of cells with LSM cathodes due to their high activation energies. LSCF is a mixed ionic electronic conducting perovskite that exhibits higher performance than LSM/YSZ composites and shows potential as a replacement cathode. This study investigates the effect of A-site stoichiometry on the performance of LSCF cathodes. Cell tests showed that A-site and Sr-deficient LSCF cathodes consistently outperformed stoichiometric LSCF cathodes, exhibiting up to 10% higher cell power densities. It was also observed that all stoichiometric, A-site, and Sr-deficient LSCF cathodes degraded over time at similar rates. Contributions of ohmic and electrode polarization losses to cell degradation rates were similar regardless of cathode composition.

  5. Effect of Applied Current Density on Morphological and Structural Properties of Electrodeposited Fe-Cu Films

    Institute of Scientific and Technical Information of China (English)

    Umut Sarac; M. Celalettin Baykul

    2012-01-01

    A detailed study has been carried out to investigate the effect of applied current density on the composition, crystallographic structure, grain size, and surface morphology of Fe-Cu films. X-ray diffraction (XRD) results show that the films consist of a mixture of face-centered cubic (fcc) Cu and body centered cubic (bcc) ~-Fe phases. The average crystalline size of both Fe and Cu particles decreases as the applied current density becomes more negative. Compositional analysis of Fe-Cu films indicates that the Fe content within the films increases with decreasing current density towards more negative values. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used to investigate the surface morphology of Fe-Cu films. It is observed that the surface morphology of the films changes from dendritic structure to a cauliflower structure as the applied current density becomes more negative. The surface roughness and grain size of the Fe-Cu films decrease with decreasing applied current density towards more negative values.

  6. Induced fermionic charge and current densities in two-dimensional rings

    CERN Document Server

    Bellucci, S; Grigoryan, A Kh

    2016-01-01

    For a massive quantum fermionic field, we investigate the vacuum expectation values (VEVs) of the charge and current densities induced by an external magnetic flux in a two-dimensional circular ring. Both the irreducible representations of the Clifford algebra are considered. On the ring edges the bag (infinite mass) boundary conditions are imposed for the field operator. This leads to the Casimir type effect on the vacuum characteristics. The radial current vanishes. The charge and the azimuthal current are decomposed into the boundary-free and boundary-induced contributions. Both these contributions are odd periodic functions of the magnetic flux with the period equal to the flux quantum. An important feature that distinguishes the VEVs of the charge and current densities from the VEV of the energy density, is their finiteness on the ring edges. The current density is equal to the charge density for the outer edge and has the opposite sign on the inner edge. The VEVs are peaked near the inner edge and, as f...

  7. LORETA current source density for duration mismatch negativity and neuropsychological assessment in early schizophrenia.

    Directory of Open Access Journals (Sweden)

    Tomohiro Miyanishi

    Full Text Available INTRODUCTION: Patients with schizophrenia elicit cognitive decline from the early phase of the illness. Mismatch negativity (MMN has been shown to be associated with cognitive function. We investigated the current source density of duration mismatch negativity (dMMN, by using low-resolution brain electromagnetic tomography (LORETA, and neuropsychological performance in subjects with early schizophrenia. METHODS: Data were obtained from 20 patients meeting DSM-IV criteria for schizophrenia or schizophreniform disorder, and 20 healthy control (HC subjects. An auditory odd-ball paradigm was used to measure dMMN. Neuropsychological performance was evaluated by the brief assessment of cognition in schizophrenia Japanese version (BACS-J. RESULTS: Patients showed smaller dMMN amplitudes than those in the HC subjects. LORETA current density for dMMN was significantly lower in patients compared to HC subjects, especially in the temporal lobes. dMMN current density in the frontal lobe was positively correlated with working memory performance in patients. CONCLUSIONS: This is the first study to identify brain regions showing smaller dMMN current density in early schizophrenia. Further, poor working memory was associated with decreased dMMN current density in patients. These results are likely to help understand the neural basis for cognitive impairment of schizophrenia.

  8. Cathode materials review

    International Nuclear Information System (INIS)

    The electrochemical potential of cathode materials defines the positive side of the terminal voltage of a battery. Traditionally, cathode materials are the energy-limiting or voltage-limiting electrode. One of the first electrochemical batteries, the voltaic pile invented by Alessandro Volta in 1800 (Phil. Trans. Roy. Soc. 90, 403-431) had a copper-zinc galvanic element with a terminal voltage of 0.76 V. Since then, the research community has increased capacity and voltage for primary (nonrechargeable) batteries and round-trip efficiency for secondary (rechargeable) batteries. Successful secondary batteries have been the lead-acid with a lead oxide cathode and a terminal voltage of 2.1 V and later the NiCd with a nickel(III) oxide-hydroxide cathode and a 1.2 V terminal voltage. The relatively low voltage of those aqueous systems and the low round-trip efficiency due to activation energies in the conversion reactions limited their use. In 1976, Wittingham (J. Electrochem. Soc., 123, 315) and Besenhard (J. Power Sources 1(3), 267) finally enabled highly reversible redox reactions by intercalation of lithium ions instead of by chemical conversion. In 1980, Goodenough and Mizushima (Mater. Res. Bull. 15, 783-789) demonstrated a high-energy and high-power LiCoO2 cathode, allowing for an increase of terminal voltage far beyond 3 V. Over the past four decades, the international research community has further developed cathode materials of many varieties. Current state-of-the-art cathodes demonstrate voltages beyond any known electrolyte stability window, bringing electrolyte research once again to the forefront of battery research

  9. Bilirubin oxidase based enzymatic air-breathing cathode: Operation under pristine and contaminated conditions

    OpenAIRE

    Santoro, Carlo; Babanova, Sofia; Erable, Benjamin; Schuler, Andrew; Atanassov, Plamen

    2016-01-01

    The performance of bilirubin oxidase (BOx) based air breathing cathode was constantly monitored over 45 days. The effect of electrolyte composition on the cathode oxygen reduction reaction (ORR) output was investigated. Particularly, deactivation of the electrocatalytic activity of the enzyme in phosphate buffer saline (PBS) solution and in activated sludge (AS) was evaluated. The greatest drop in current density was observed during the first 3 days of constant operation with a decrease of ~6...

  10. Estimation of nighttime dip-equatorial E-region current density using measurements and models

    Science.gov (United States)

    Pandey, Kuldeep; Sekar, R.; Anandarao, B. G.; Gupta, S. P.; Chakrabarty, D.

    2016-08-01

    The existence of the possible ionospheric current during nighttime over low-equatorial latitudes is one of the unresolved issues in ionospheric physics and geomagnetism. A detailed investigation is carried out to estimate the same over Indian longitudes using in situ measurements from Thumba (8.5 ° N, 76.9 ° E), empirical plasma drift model (Fejer et al., 2008) and equatorial electrojet model developed by Anandarao (1976). This investigation reveals that the nighttime E-region current densities vary from ∼0.3 to ∼0.7 A/km2 during pre-midnight to early morning hours on geomagnetically quiet conditions. The nighttime current densities over the dip equator are estimated using three different methods (discussed in methodology section) and are found to be consistent with one another within the uncertainty limits. Altitude structures in the E-region current densities are also noticed which are shown to be associated with altitudinal structures in the electron densities. The horizontal component of the magnetic field induced by these nighttime ionospheric currents is estimated to vary between ∼2 and ∼6 nT during geomagnetically quiet periods. This investigation confirms the existence of nighttime ionospheric current and opens up a possibility of estimating base line value for geomagnetic field fluctuations as observed by ground-based magnetometer.

  11. Determination of the heat-transfer coefficient and current density profile of gas-discharge plasma

    International Nuclear Information System (INIS)

    The spatial distribution of gas temperature in a cylindrical discharge tube is theoretically investigated in respect of heat transfer due to gas thermal conduction and heat exchange with surrounding medium. Based on the obtained results the facilities for experimental determination of the heat-transfer coefficient of gas-discharge plasma and radial profiles of the electron density, discharge current density and radiants are shown

  12. Simultaneous Observations of Electric Fields, Current Density, Plasma Density, and Neutral Winds During Two Sounding Rocket Experiments Launched from Wallops Island into Strong Daytime Dynamo Currents

    Science.gov (United States)

    Pfaff, R. F., Jr.; Rowland, D. E.; Klenzing, J.; Freudenreich, H. T.; Martin, S. C.; Abe, T.; Habu, H.; Yamamoto, M. Y.; Watanabe, S.; Yamamoto, M.; Yokoyama, T.; Kakinami, Y.; Yamazaki, Y.; Larsen, M. F.; Hurd, L.; Clemmons, J. H.; Bishop, R. L.; Walterscheid, R. L.; Fish, C. S.; Bullett, T. W.; Mabie, J. J.; Murphy, N.; Angelopoulos, V.; Leinweber, H. K.; Bernal, I.; Chi, P. J.

    2015-12-01

    To investigate the ion-neutral coupling that creates the global electrical daytime "dynamo" currents in the mid-latitude, lower ionosphere, NASA carried out two multiple sounding rocket experiments from Wallops Island, VA on July 10, 2011 (14:00 UT, 10:00 LT) and July 4, 2013 (14:31 UT, 10:31 LT). The rockets were launched in the presence of well-defined, westward Hall currents observed on the ground with ΔH values of ­-25 nT and -30 nT, respectively, as well as a well-defined, daytime ionospheric density observed by the VIPIR ionosonde at Wallops. During the 2011 experiment, a narrow, intense sporadic-E layer was observed near 102 km. Each experiment consisted of a pair of rockets launched 15 sec apart. The first rocket of each pair carried instruments to measure DC electric and magnetic fields, as well as the ambient plasma and neutral gases and attained apogees of 158 km and 135 km in the 2011 and 2013 experiments, respectively. The second rocket of each pair carried canisters which released a lithium vapor trail along the upleg to illuminate neutral winds in the upper atmosphere. This daytime vapor trail technology was developed jointly by researchers at JAXA and Clemson University. In the second experiment, the lithium release was clearly visible in cameras with infrared filters operated by US and Japanese researchers in a NASA airplane at 9.6 km altitude. The observed wind profiles reached speeds of 100 m/s with strong shears with respect to altitude and were consistent with an independent derivation of the wind from the ionization gauge sensor suite on the instrumented rocket. The "vapor trail" rockets, which also included a falling sphere, attained apogees of 150 km and 143 km in the 2011 and 2013 experiments, respectively. By measuring the current density, conductivity, DC electric fields, and neutral winds, we solve the dynamo equation as a function of altitude, revealing the different contributions to the lower E-region currents. We find that the DC

  13. Effects of pulse-length and emitter area on virtual cathode formation in electron guns

    Science.gov (United States)

    Valfells, Ágúst; Feldman, D. W.; Virgo, M.; O'Shea, P. G.; Lau, Y. Y.

    2002-05-01

    Recent experiments at the University of Maryland using photoemission from a dispenser cathode have yielded some interesting results regarding the effects of the area of emission and of the ratio between the pulse length and the gap transit time on the amount of current that may be drawn from an electron gun before a virtual cathode forms. The experiments show that a much higher current density may be drawn from a short pulse or limited emitter area than is anticipated by the Child-Langmuir limiting current. There is also evidence that the current may be increased even after virtual cathode formation, which leads a distinction between a limiting current density and a current density critical for virtual cathode formation. The experiments have also yielded some interesting results on the longitudinal structure of the current pulse passed through the anode. Some empirical and theoretical scaling laws regarding the formation of virtual cathodes in an electron gun will be presented. This work was motivated by the needs of the University of Maryland Electron Ring (UMER) [P. G. O'Shea, M. Reiser, R. A. Kishek et al., Nucl. Instrum. Methods Phys. Res. A 464, 646 (2001)] where the goal is to generate pulses that are well-localized in time and space.

  14. Effects of pulse-length and emitter area on virtual cathode formation in electron guns

    International Nuclear Information System (INIS)

    Recent experiments at the University of Maryland using photoemission from a dispenser cathode have yielded some interesting results regarding the effects of the area of emission and of the ratio between the pulse length and the gap transit time on the amount of current that may be drawn from an electron gun before a virtual cathode forms. The experiments show that a much higher current density may be drawn from a short pulse or limited emitter area than is anticipated by the Child-Langmuir limiting current. There is also evidence that the current may be increased even after virtual cathode formation, which leads a distinction between a limiting current density and a current density critical for virtual cathode formation. The experiments have also yielded some interesting results on the longitudinal structure of the current pulse passed through the anode. Some empirical and theoretical scaling laws regarding the formation of virtual cathodes in an electron gun will be presented. This work was motivated by the needs of the University of Maryland Electron Ring (UMER) [P. G. O'Shea, M. Reiser, R. A. Kishek et al., Nucl. Instrum. Methods Phys. Res. A 464, 646 (2001)] where the goal is to generate pulses that are well-localized in time and space

  15. The current density in quantum electrodynamics in time-dependent external potentials and the Schwinger effect

    International Nuclear Information System (INIS)

    In the framework of quantum electrodynamics (QED) in external potentials, we introduce a method to compute the time-dependence of the expectation value of the current density for time-dependent homogeneous external electric fields. We apply it to the so-called Sauter pulse. For late times, our results agree with the asymptotic value due to electron-positron pair production. We correct a general expression derived by Serber for the expectation value of the current, linearized in the external field, and compare with our results for the Sauter pulse. Based on the properties of the current density, we argue that the appearance of enhanced quasi-particle densities at intermediate times in slowly varying sub-critical potentials is generic. Also an alternative approach, which circumvents these difficulties, is sketched. (paper)

  16. Effects of Current Density on Microstructure of Titania Coatings by Micro-arc Oxidation

    Institute of Scientific and Technical Information of China (English)

    Yue Yang; Hua Wu

    2012-01-01

    In the present study, titania coatings were prepared under different current density conditions in micro-arc oxidation (MAO) process on titanium alloy in NaAlO2 solution. The aim of this work was to study the effects of current density on the microstructure of titania coatings. The morphology and phase composition of the coatings were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectra. The thickness and surface roughness of the coatings were characterized by confocal laser Scanning Microscopy (CLSM). The results showed that the coatings were composed of crystalline anatase and rutile phases of TiO2, and contain a network of evenly distributed small pores. It has also shown that an increase in current density leads to an increase in rutile content.

  17. Analysis of current density and related parameters in spinal cord stimulation.

    Science.gov (United States)

    Wesselink, W A; Holsheimer, J; Boom, H B

    1998-06-01

    A volume conductor model of the spinal cord and surrounding anatomical structures is used to calculate current (and current density) charge per pulse, and maximum charge density per pulse at the contact surface of the electrode in the dorsal epidural space, in the dorsal columns of the spinal cord and in the dorsal roots. The effects of various contact configurations (mono-, bi-, and tripole), contact area and spacing, pulsewidth and distance between contacts and spinal cord on these electrical parameters were investigated under conditions similar to those in clinical spinal cord stimulation. At the threshold stimulus of a large dorsal column fiber, current density and charge density per pulse at the contact surface were found to be highest (1.9.10(5) microA/cm2 and 39.1 microC/cm2.p, respectively) when the contact surface was only 0.7 mm2. When stimulating with a pulse of 500 microseconds, highest charge per pulse (0.92 microC/p), and the largest charge density per pulse in the dorsal columns (1.59 microC/cm2. p) occurred. It is concluded that of all stimulation parameters that can be selected freely, only pulsewidth affects the charge and charge density per pulse in the nervous tissue, whereas both pulsewidth and contact area strongly affect these parameters in the nonnervous tissue neighboring the electrode contacts. PMID:9631328

  18. The Effect of Current Density on CNx Crystal Grain Growth in Electrochemical Deposition

    International Nuclear Information System (INIS)

    The effect of charge current density on the growth of CNx films by electrolysis of a methanol-urea solution is investigated experimentally. It is seen that the C-C3N4 phase grains in the films are about 200–300 nm for a density of 55 mA/cm2 and dendrite growth takes place with grains as large as 7 μm formed when density is about 70 mA/cm2. (cross-disciplinary physics and related areas of science and technology)

  19. Critical current density of Bi-2212 thick films processed by partial melting

    International Nuclear Information System (INIS)

    Bi2Sr2CaCu2O8+δ (Bi-2212) thick films were produced via tape casting and partial melting. The aim of the study was to investigate the influence of the different heat treatment steps on the critical current density of the films. Five processing parameters were studied: maximum densification temperature, cooling rate during crystallization, annealing time after crystallization, reduction treatment and processing atmosphere. It will also be demonstrated that the critical current density strongly depends on the sample thickness. In 20 μm thick films we achieved 20,000 A cm-2 at 77 K - 0 T and 300,000 A cm-2 at 10 K - 0 T. The critical current density at 77 K - 0 T dropped to 6200 A cm-2 in 130 μm thick films and levelled out at 3000 A cm-2 in bulk samples thicker than 500 μm. These high critical current densities were reached only using a narrow processing window. The maximum densification temperature had to be within 5 - 10 deg. C above the solidus temperature (875 deg. C). Cooling from the maximum temperature to an annealing temperature of 850 deg. C had to be around 5 to 10 deg. C h-1 and the final annealing step was prolonged up to 70 h to optimize the critical current density. All processing steps were carried out in pure oxygen (1 atm) except the last step, reduction annealing at 500 deg. C for 20 h, that was performed in nitrogen (p(O2) approx. 0.01 atm). Processing in air (p(O2) = 0.21 atm) instead of oxygen leads to strongly decreased critical current densities in the high-temperature region above 30 K. (author)

  20. The study of dynamics of electrons in the presence of large current densities

    International Nuclear Information System (INIS)

    The runaway electron effect is considered in different fields: nuclear fusion, or the heating of the solar corona. In this thesis, we are interested in runaway electrons in the ionosphere. We consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a parallel electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. A computational example is given illustrating the approach to equilibrium and the impact of the different terms. Then, a static electric field is applied in a new sample run. In this run, the electrons move in the z direction, parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density up to 20% of the total current density. Nevertheless, we note that the divergence free of the current density is not conserved. We introduce major changes in order to take into account the variation of the different moments of the ion distribution functions. We observe that the electron distribution functions are still non-Maxwellian. Runaway electrons are created and carry the current density. The core distribution stay at rest. As these electrons undergo less collisions, they increase the plasma conductivity. We make a parametric study. We fit the electron distribution function by two Maxwellian. We show that the time to reach the maximal current density is a key point. Thus, when we increase this time, we modify the temperatures. The current density plays a primary role. When the current density increases, all the moments of the distributions increase: electron density and mean velocity of the suprathermal distribution and the electron temperature of the core and

  1. Ion Current Density Calculation of the Inductive Radio Frequency Ion Source

    Directory of Open Access Journals (Sweden)

    V.I. Voznyi

    2012-10-01

    Full Text Available A radio-frequency (RF inductive ion source at 27.12 MHz is investigated. With a global model of the argon discharge, plasma density, electron temperature and ion current density of the ion source is calculated in relation to absorbed RF power and gas pressure as a discharge chamber size changes. It is found that ion beam current density grows as the discharge chamber size decreases. Calculations show that in the RF source with a discharge chamber 30 mm in diameter and 35 mm long the ion current density is 40 mA/cm2 at 100 W of absorbed RF power and 7 mTorr of pressure, and agrees well with experimentally measured value of 43 mA/cm2. With decreasing discharge chamber diameter to 15 mm ion current density can reach 85 mA/cm2 at absorbed RF power of 100 W.

  2. Improved field emission properties of carbon nanotube cathodes by nickel electroplating and corrosion

    Science.gov (United States)

    Xiaojing, Xiao; Yun, Ye; Longwu, Zheng; Tailiang, Guo

    2012-05-01

    Carbon nanotube (CNT) cathodes prepared by electrophoretic deposition were treated by a combination of nickel electroplating and cathode corrosion technologies. The characteristics of the samples were measured by scanning electron microscopy, energy dispersive X-ray spectroscopy, J-E and F—N plots. After the treatment, the CNT cathodes showed improved field emission properties such as turn-on field, threshold electric field, current density, stability and luminescence uniformity. Concretely, the turn-on field decreased from 0.95 to 0.45 V/μm at an emission current density of 1 mA/cm2, and the threshold electric field decreased from 0.99 to 0.46 V/μm at a current density of 3 mA/cm2. The maximum current density was up to 7 mA/cm2 at a field of 0.48 V/μm. In addition, the current density of the CNT cathodes fluctuated at around 0.7 mA/cm2 for 20 h, with an initial current density 0.75 mA/cm2. The improvement in field emission properties was found to be due to the exposure of more CNT tips, the wider gaps among the CNTs and the infiltration of nickel particles.

  3. Experimental investigation of dynamic responses of a transparent PEM fuel cell to step changes in cell current density with operating temperature

    International Nuclear Information System (INIS)

    The dynamic responses of a proton exchange membrane fuel cell (PEMFC) are closely related to the novel water management technique used for the efficient operation of automotive PEMFCs. In order to better understand the dynamic water transport during cell transients, this paper presents an experimental investigation of the transient response of a cell under fully humidified conditions. The cell dynamic performance was measured by employing a transparent cell and investigated with visualization images of the water distribution in the flow channels. Furthermore, the effect of the operating temperature on the cell transients was examined. The results show that the cell dynamic behavior for the tested operating temperature (30-50 .deg. C) conditions is mainly governed by water transport characteristics related to cathode flooding. Also, we show that the time needed for the cell to reach steady-state after a current density step increase is retarded due to excessive water accumulation inside the cell at lower operating temperatures

  4. Pressure limits of negative ion sources based upon gas efficiency and extracted ion-current density

    International Nuclear Information System (INIS)

    The nature of the electrical discharge has an obvious impact upon the gas efficiency of an ion source and on the current density whch can be drawn from it. However external factors, such as the conductance of the grids and the background pressure along the beamline, also have an effect. Simple approximations based upon these factors show that there is a lower limit to the pressure of an ion source, which can deliver an ion beam of given current density at a specific gas efficiency. Estimates of ion stripping losses in a double gridded structure show that for all practical purposes, there is an upper limit as well

  5. MHD Equilibrium with Reversed Current Density and Magnetic Islands Revisited: the Vacuum Vector Potential Calculus

    International Nuclear Information System (INIS)

    The solution of Grad-Shafranov equation determines the stationary behavior of fusion plasma inside a tokamak. To solve the equation it is necessary to know the toroidal current density profile. Recent works show that it is possible to determine a magnetohydrodynamic (MHD) equilibrium with reversed current density (RCD) profiles that presents magnetic islands. In this work we show analytical MHD equilibrium with a RCD profile and analyze the structure of the vacuum vector potential associated with these equilibria using the virtual casing principle

  6. MHD Equilibrium with Reversed Current Density and Magnetic Islands Revisited: the Vacuum Vector Potential Calculus

    Science.gov (United States)

    L. Braga, F.

    2013-10-01

    The solution of Grad-Shafranov equation determines the stationary behavior of fusion plasma inside a tokamak. To solve the equation it is necessary to know the toroidal current density profile. Recent works show that it is possible to determine a magnetohydrodynamic (MHD) equilibrium with reversed current density (RCD) profiles that presents magnetic islands. In this work we show analytical MHD equilibrium with a RCD profile and analyze the structure of the vacuum vector potential associated with these equilibria using the virtual casing principle.

  7. Multipole lenses with implicit poles and with harmonic distribution of current density in a coil

    International Nuclear Information System (INIS)

    General theory of the multipole lense with implicit poles is presented. The thickness of lense coil is finite. Current density distribution in the coil cross section is harmonic in the azimuth direction and arbitrary in the radial one. The calculation of yoke contribution in the lence field is given. Two particular lense variants differing from each other in the method of current density radial distribution are considered and necessary calculated relations for the lense with and without yoke ar presented. A comparative analysis of physical and technological peculiarities of these lenses is performed

  8. Air-cathode structure optimization in separator-coupled microbial fuel cells

    KAUST Repository

    Zhang, Xiaoyuan

    2011-12-01

    Microbial fuel cells (MFC) with 30% wet-proofed air cathodes have previously been optimized to have 4 diffusion layers (DLs) in order to limit oxygen transfer into the anode chamber and optimize performance. Newer MFC designs that allow close electrode spacing have a separator that can also reduce oxygen transfer into the anode chamber, and there are many types of carbon wet-proofed materials available. Additional analysis of conditions that optimize performance is therefore needed for separator-coupled MFCs in terms of the number of DLs and the percent of wet proofing used for the cathode. The number of DLs on a 50% wet-proofed carbon cloth cathode significantly affected MFC performance, with the maximum power density decreasing from 1427 to 855mW/m 2 for 1-4 DLs. A commonly used cathode (30% wet-proofed, 4 DLs) produced a maximum power density (988mW/m 2) that was 31% less than that produced by the 50% wet-proofed cathode (1 DL). It was shown that the cathode performance with different materials and numbers of DLs was directly related to conditions that increased oxygen transfer. The coulombic efficiency (CE) was more affected by the current density than the oxygen transfer coefficient for the cathode. MFCs with the 50% wet-proofed cathode (2 DLs) had a CE of >84% (6.8A/m 2), which was substantially larger than that previously obtained using carbon cloth air-cathodes lacking separators. These results demonstrate that MFCs constructed with separators should have the minimum number of DLs that prevent water leakage and maximize oxygen transfer to the cathode. © 2011 Elsevier B.V.

  9. Ring Current Density Distribution and Coupling with Radiation Belts Plasma Population

    Science.gov (United States)

    Bogdanova, Yulia; Dunlop, Malcolm; Perry, Chris; Fazakerley, Andrew; Klecker, Berndt; Mouikis, Christopher; Zhang, Qinghe; Shen, Chao

    2015-04-01

    The ring current, a toroidal current system centred at the equatorial plane at geocentric distances between ~2Re and ~9Re, is formed due to the gradient and curvature drifts of the energetic particles trapped in the inner magnetosphere. The radiation belts and ring current are closely related, and it has been shown previously that a subset of the radiation belt population, ions in the medium-energy range, from ~ 10 keV to a few hundreds of keV, contribute the most towards the total ring current energy density, with the O+ ions contribution increasing strongly from 6% to 21% during active times (Daglis et al., 1993). In this work we use unique Cluster observations from the beginning of the mission (2002-2004), with the Cluster satellites often crossing the outer radiation belt and ring current region at L-shell ~ 4 Re. At that time the Cluster tetrahedron geometry was well suited for estimations of the total ring current density and azimuthal current density from the measurements of the magnetic field, using the curlometer technique (Dunlop et al., 2002). We combine the estimations of the current density with the observations of ion and electron populations from the RAPID, CIS and PEACE instruments inside the radiation belts in order to gain additional information on the relative contributions of ions and electrons of different energies towards the ring current strength. Results for a number of cases are presented, including different MLT sectors and levels of geomagnetic activity. The changes in the particle distribution for low and high geomagnetic activity levels will be discussed.

  10. Combined current and temperature mapping in an air-cooled, open-cathode polymer electrolyte fuel cell under steady-state and dynamic conditions

    Science.gov (United States)

    Meyer, Q.; Ronaszegi, K.; Robinson, J. B.; Noorkami, M.; Curnick, O.; Ashton, S.; Danelyan, A.; Reisch, T.; Adcock, P.; Kraume, R.; Shearing, P. R.; Brett, D. J. L.

    2015-11-01

    In situ diagnostic techniques provide a means of understanding the internal workings of fuel cells so that improved designs and operating regimes can be identified. Here, for the first time, a combined current density and temperature distributed measurement system is used to generate an electro-thermal performance map of an air-cooled, air-breathing polymer electrolyte fuel cell stack operating in an air/hydrogen cross-flow configuration. Analysis is performed in low- and high-current regimes and a complex relationship between localised current density, temperature and reactant supply is identified that describes the way in which the system enters limiting performance conditions. Spatiotemporal analysis was carried out to characterise transient operations in dead-ended anode/purge mode which revealed extensive current density and temperature gradients.

  11. Power generation using carbon mesh cathodes with different diffusion layers in microbial fuel cells

    KAUST Repository

    Luo, Yong

    2011-11-01

    An inexpensive carbon material, carbon mesh, was examined to replace the more expensive carbon cloth usually used to make cathodes in air-cathode microbial fuel cells (MFCs). Three different diffusion layers were tested using carbon mesh: poly(dimethylsiloxane) (PDMS), polytetrafluoroethylene (PTFE), and Goretex cloth. Carbon mesh with a mixture of PDMS and carbon black as a diffusion layer produced a maximum power density of 1355 ± 62 mW m -2 (normalized to the projected cathode area), which was similar to that obtained with a carbon cloth cathode (1390 ± 72 mW m-2). Carbon mesh with a PTFE diffusion layer produced only a slightly lower (6.6%) maximum power density (1303 ± 48 mW m-2). The Coulombic efficiencies were a function of current density, with the highest value for the carbon mesh and PDMS (79%) larger than that for carbon cloth (63%). The cost of the carbon mesh cathode with PDMS/Carbon or PTFE (excluding catalyst and binder costs) is only 2.5% of the cost of the carbon cloth cathode. These results show that low cost carbon materials such as carbon mesh can be used as the cathode in an MFC without reducing the performance compared to more expensive carbon cloth. © 2011 Elsevier B.V.

  12. Microstructure and properties of a Mo-CeO2 heated cathode material

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jiuxing; WAN Xiaofeng; LI Xiangbo; ZHOU Wenyuan; ZHOU Meiling

    2004-01-01

    The microstructure, mechanical properties, and electron-emission properties of a newly developed heated cath ode material Mo-CeO2 with 4.0% (mass fraction) of CeO2 were investigated. It is shown that the Mo-CeO2 cathode material possesses high tensile strength and good room-temperature ductility. After carbonized, the Mo-CeO2 cathode material has a higher zero field emission current density and a lower work function compared with the W-ThO2 cathode material.

  13. The electrical current density vector in the inner penumbra of a Sunspot

    CERN Document Server

    Puschmann, K G; Pillet, V Martínez

    2010-01-01

    We determine the entire electrical current density vector in a geometrical 3D volume of the inner penumbra of a sunspot from an inversion of spectropolarimetric data obtained with Hinode/SP. Significant currents are seen to wrap around the hotter, more elevated regions with lower and more horizontal magnetic field that harbor strong upflows and radial outflows (the intraspines). The horizontal component of the current density vector is 3-4 times larger than the vertical; nearly all previous studies only obtain the vertical component and thus strongly underestimate the current density. The current density and the magnetic field vectors form an angle of about 20 degrees. The plasma beta at the 0 km level is larger than 1 in the intraspines and is one order of magnitude lower in the background component of the penumbra (spines). At the 200 km level, the plasma beta is below 0.3 nearly everywhere. The plasma beta surface as well as the surface optical depth unity are very corrugated. At the borders of intraspines...

  14. THE ELECTRICAL CURRENT DENSITY VECTOR IN THE INNER PENUMBRA OF A SUNSPOT

    International Nuclear Information System (INIS)

    We determine the entire electrical current density vector in a geometrical three-dimensional volume of the inner penumbra of a sunspot from an inversion of spectropolarimetric data obtained with Hinode/SP. Significant currents are seen to wrap around the hotter, more elevated regions with lower and more horizontal magnetic fields that harbor strong upflows and radial outflows (the intraspines). The horizontal component of the current density vector is 3-4 times larger than the vertical; nearly all previous studies only obtain the vertical component Jz , thus strongly underestimating the current density. The current density J-vector and the magnetic field B-vector form an angle of about 200. The plasma β at the 0 km level is larger than 1 in the intraspines and is one order of magnitude lower in the background component of the penumbra (spines). At the 200 km level, the plasma β is below 0.3, nearly everywhere. The plasma β surface as well as the surface optical depth unity is very corrugated. At the borders of intraspines and inside, B-vector is not force-free at deeper layers and nearly force-free at the top layers. The magnetic field of the spines is close to being potential everywhere. The dissipated ohmic energy is five orders of magnitudes smaller than the solar energy flux and thus negligible for the energy balance of the penumbra.

  15. Use of Pyrolyzed Iron Ethylenediaminetetraacetic Acid Modified Activated Carbon as Air–Cathode Catalyst in Microbial Fuel Cells

    KAUST Repository

    Xia, Xue

    2013-08-28

    Activated carbon (AC) is a cost-effective catalyst for the oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). To enhance the catalytic activity of AC cathodes, AC powders were pyrolyzed with iron ethylenediaminetetraacetic acid (FeEDTA) at a weight ratio of FeEDTA:AC = 0.2:1. MFCs with FeEDTA modified AC cathodes and a stainless steel mesh current collector produced a maximum power density of 1580 ± 80 mW/m2, which was 10% higher than that of plain AC cathodes (1440 ± 60 mW/m 2) and comparable to Pt cathodes (1550 ± 10 mW/m2). Further increases in the ratio of FeEDTA:AC resulted in a decrease in performance. The durability of AC-based cathodes was much better than Pt-catalyzed cathodes. After 4.5 months of operation, the maximum power density of Pt cathode MFCs was 50% lower than MFCs with the AC cathodes. Pyridinic nitrogen, quaternary nitrogen and iron species likely contributed to the increased activity of FeEDTA modified AC. These results show that pyrolyzing AC with FeEDTA is a cost-effective and durable way to increase the catalytic activity of AC. © 2013 American Chemical Society.

  16. Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells

    Science.gov (United States)

    Wang, Z. H.; Wang, C. Y.; Chen, K. S.

    Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Single- and two-phase regimes of water distribution and transport are classified by a threshold current density corresponding to first appearance of liquid water at the membrane/cathode interface. When the cell operates above the threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multicomponent mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone of the hydrophilic structure. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A cm -2 for dry inlet air.

  17. Back bombardment for dispenser and lanthanum hexaboride cathodes

    Science.gov (United States)

    Bakr, Mahmoud; Kinjo, R.; Choi, Y. W.; Omer, M.; Yoshida, K.; Ueda, S.; Takasaki, M.; Ishida, K.; Kimura, N.; Sonobe, T.; Kii, T.; Masuda, K.; Ohgaki, H.; Zen, H.

    2011-06-01

    The back bombardment (BB) effect limits wide usage of thermionic rf guns. The BB effect induces not only ramping-up of a cathode’s temperature and beam current, but also degradation of cavity voltage and beam energy during a macropulse. This paper presents a comparison of the BB effect for the case of dispenser tungsten-base (DC) and lanthanum hexaboride (LaB6) thermionic rf gun cathodes. For each, particle simulation codes are used to simulate the BB effect and electron beam dynamics in a thermionic rf gun cathode. A semiempirical equation is also used to investigate the stopping range and deposited heat power of BB electrons in the cathode material. A numerical simulation method is used to calculate the change of the cathode temperature and current density during a single macropulse. This is done by solving two differential equations for the rf gun cavity equivalent circuit and one-dimensional thermal diffusion equation. High electron emission and small beam size are required for generation of a high-brightness electron beam, and so in this work the emission properties of the cathode are taken into account. Simulations of the BB effect show that, for a pulse of 6μs duration, the DC cathode experiences a large change in the temperature compared with LaB6, and a change in current density 6 times higher. Validation of the simulation results is performed using experimental data for beam current beyond the gun exit. The experimental data is well reproduced using the simulation method.

  18. Induced change of critical current density profile in Nb/Al-AlOx/Nb Josephson junctions

    International Nuclear Information System (INIS)

    A technique to induce spatial modulation of critical current density in niobium based Josephson devices by using a selective thermal annealing is reported. By depositing a carbon film onto selected region of the Josephson element it is possible to induce a localized heating, with a spatial resolution less than 1 μm, exploiting the much higher absorbance coefficient of carbon than the niobium one. The effectiveness of such technique is demonstrated by experimental measurement of the critical current vs. magnetic field, measured at T = 4.2 K, showing that the change of critical current density occurs only in the region corresponding to the absorber film area. Furthermore, the theoretical behaviour, by modelling a suitable step-like junction barrier shape, has been carried out to fit the experimental data in order to verify the selective modulation of critical current. This technique can be very useful in view of quantum computing experiments, Majorana fermions detection and superconducting magnetic sensors.

  19. Effect of current density on distribution coefficient of solute at solid-liquid interface

    Institute of Scientific and Technical Information of China (English)

    常国威; 王自东; 吴春京; 胡汉起

    2003-01-01

    When current passes through the solid-liquid interface, the growth rate of crystal, solid-liquid interfaceenergy and radius of curvature at dendritic tip will change. Based on this fact, the theoretical relation between thedistribution of solute at solid-liquid interface and current density was established, and the effect of current on thedistribution coefficient of solute through effecting the rate of crystal growth, the solid-liquid interface energy and theradius of curvature at the dendritic tip was discussed. The results show that as the current density increases, thedistribution coefficient of solute tends to rise in a whole, and when the former is larger than about 400 A/cm2 , thelatter varies significantly.

  20. The hollow cathode in the quasi-steady MPD discharge

    Science.gov (United States)

    Von Jaskowsky, W. F.; Jahn, R. G.; Clark, K. E.; Krishnan, M.

    1973-01-01

    A large hollow cathode has been operated in a quasi-steady MPD discharge over a range of current from 7 to 30 kA and argon mass flow from 0.04 to 6.0 g/sec. The 1.3-cm-i.d. cathode cavity attains steady emission characteristics in some tens of microseconds without the assistance of auxiliary heating, low work function inserts, or external keeper electrodes. Measured current and potential distributions within the cavity reveal that the current attaches in a zone 1 to 2 cm long with a surface current density greater than 1000 A/sq cm and a local axial electric field less than 10 V/cm. Electron densities within the cavity, estimated from spectroscopic records, are above 10 to the 17th power per cu cm, at least one order of magnitude greater than has been reported for either ion engine hollow cathodes or conventional solid cathodes in similar arc discharges.

  1. Estimation of localized current anomalies in polymer electrolyte fuel cells from magnetic flux density measurements

    Science.gov (United States)

    Nara, Takaaki; Koike, Masanori; Ando, Shigeru; Gotoh, Yuji; Izumi, Masaaki

    2016-05-01

    In this paper, we propose novel inversion methods to estimate defects or localized current anomalies in membrane electrode assemblies (MEAs) in polymer electrolyte fuel cells (PEFCs). One method is an imaging approach with L1-norm regularization that is suitable for estimation of focal anomalies compared to Tikhonov regularization. The second is a complex analysis based method in which multiple pointwise current anomalies can be identified directly and algebraically from the measured magnetic flux density.

  2. Lateral current density fronts in asymmetric double-barrier resonant-tunneling structures

    OpenAIRE

    Rodin, Pavel; Schoell, Eckehard

    2003-01-01

    We present a theoretical analysis and numerical simulations of lateral current density fronts in bistable resonant-tunneling diodes with Z-shaped current-voltage characteristics. The bistability is due to the charge accumulation in the quantum well of the double-barrier structure. We focus on asymmetric structures in the regime of sequential incoherent tunneling and study the dependence of the bistability range, the front velocity and the front width on the structure parameters. We propose a ...

  3. Small Barriers Trigger Liftoff of Unconfined Dilute Heated Laboratory Density Currents

    Science.gov (United States)

    Fauria, K.; Andrews, B. J.; Manga, M.

    2015-12-01

    Dilute pyroclastic density currents (PDCs) are hot, turbulent, particle-laden flows that propagate because they are denser than air. PDCs can traverse tens to hundreds of kilometers and surmount ridges 100s of m tall, yet the effects of complex topography on PDC liftoff and runout distance are uncertain. Here we used scaled laboratory experiments to explore how barriers affect dilute density current dynamics and the occurrence of liftoff. We created dilute density currents by heating and suspending 20 μm diameter talc in air in an 8.5 x 6.1 x 2.6 m tank. We scaled the currents with respect to Froude, densimetric and thermal Richardson, particle Stokes and Settling numbers such that they were dynamically similar to natural PDCs. While currents were fully turbulent, their Reynolds numbers were not as high as those for natural PDCs. We performed the first set of experiments in a laterally unconfined volume, used laser sheets to illuminate the currents, measured bulk sedimentation rates down the current centerlines, and positioned four to twenty-four cm tall ridge-like barriers in the path of the currents. We found that relatively small barriers (~ half the current height) caused PDC liftoff. By comparison, conservation of kinetic and potential energy predicts that incompressible density currents are able to surmount barriers twice their height. Furthermore, we observed increased sedimentation immediately upstream of barriers and conclude that small barriers initiated buoyancy reversal through a combination of increased air entrainment and sedimentation. We conducted a second set of experiments with the same thermal scaling and mass flux rates but where the currents were laterally confined within a 0.6 m wide channel. We found that small barriers also triggered liftoff of confined currents, but that the body of these currents reattached after liftoff. Those results suggest that lateral confinement inhibits buoyancy reversal by limiting the surface area of the current

  4. Experimental study of turbulence, sedimentation, and coignimbrite mass partitioning in dilute pyroclastic density currents

    Science.gov (United States)

    Andrews, Benjamin J.; Manga, Michael

    2012-05-01

    Laboratory density currents comprising warm talc powder turbulently suspended in air simulate many aspects of dilute pyroclastic density currents (PDCs) and demonstrate links between bulk current behavior, sedimentation, and turbulent structures. The densimetric and thermal Richardson, Froude, Stokes, and settling numbers match those of natural PDCs as does the ratio of thermal to kinetic energy density. The experimental currents have lower bulk Reynolds numbers than natural PDCs, but the experiments are fully turbulent. Consequently, the experiments are dynamically similar to the dilute portions of some natural currents. In general, currents traverse the floor of the experimental tank, sedimenting particles and turbulently entraining, heating, and thermally expanding air until all particle sediments or the currents become buoyant and lift off to form coignimbrite plumes. When plumes form, currents often undergo local flow reversals. Current runout distance and liftoff position decrease with increasing densimetric Richardson number and thermal energy density. As those parameters increase, total sedimentation decreases such that > 50% of initial current mass commonly fractionates into the plumes, in agreement with some observations of recent volcanic eruptions. Sedimentation profiles are best described by an entraining sedimentation model rather than the exponential fit resulting from non-entraining box models. Time series analysis shows that sedimentation is not a constant rate process in the experiments, but rather occurs as series of sedimentation-erosion couplets that propagate across the tank floor tracking current motion and behavior. During buoyant liftoff, sedimentation beneath the rising plumes often becomes less organized. Auto-correlation analysis of time series of particle concentration is used to characterize the turbulent structures of the currents and indicates that currents quickly partition into a slow-moving upper portion and faster, more

  5. Effect of electrolysis parameters on the morphologies of copper powder obtained at high current densities

    Directory of Open Access Journals (Sweden)

    Orhan Gökhan

    2012-01-01

    Full Text Available The effects of copper ion concentrations and electrolyte temperature on the morphologies and on the apparent densities of electrolytic copper powders at high current densities under galvanostatic regime were examined. These parameters were evaluated by the current efficiency of hydrogen evolution. In addition, scanning electron microscopy was used for analyzing the morphology of the copper powders. It was found that the morphology was dependent over the copper ion concentration and electrolyte temperature under same current density (CD conditions. At 150 mA cm-2 and the potential of 1000±20 mV (vs. SCE, porous and disperse copper powders were obtained at low concentrations of Cu ions (0.120 M Cu2+ in 0.50 M H2SO4. Under this condition, high rate of hydrogen evolution reaction took place parallel to copper electrodeposition. The morphology was changed from porous, disperse and cauliflower-like to coral-like, shrub-like and stalk-stock like morphology with the increasing of Cu ion concentrations towards 0.120 M, 0.155 M, 0.315 M, 0.475 M and 0.630 M Cu2+ in 0.5 M H2SO4 respectively at the same CD. Similarly, as the temperature was increased, powder morphology and apparent density were observed to be changed. The apparent density values of copper powders were found to be suitable for many of the powder metallurgy applications.

  6. Current densities and total contact currents during forest clearing tasks under 400 kV power lines.

    Science.gov (United States)

    Korpinen, Leena; Kuisti, Harri; Elovaara, Jarmo

    2016-09-01

    The aim of the study was to analyze all values of electric currents from measured periods while performing tasks in forest clearing. The objective was also to choose and analyze measurement cases, where current measurements successfully lasted the entire work period (about 30 min). Two forestry workers volunteered to perform four forest clearing tasks under 400 kV power lines. The sampling frequency of the current measurements was 1 sample/s. The maximum values of the current densities were 1.0-1.2 mA/m(2) (calculated internal EFs 5.0-12.0 mV/m), and the average values were 0.2-0.4 mA/m(2) . The highest contact current was 167.4 μA. All measured values during forest clearing tasks were lower than basic restrictions (0.1 V/m and 0.8 V/m) of the International Commission on Non-Ionizing Radiation Protection. Bioelectromagnetics. 37:423-428, 2016. © 2016 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc. PMID:27192179

  7. Lower hybrid current ramp-up experiments and density limit on Alcator C

    International Nuclear Information System (INIS)

    Lower hybrid plasma current ramp-up efficiencies at densities n-bar/sub e/> or =1 x 1013 cm-3 are investigated. The ramp-up efficiency P/sub e//sub l//P/sub r//sub f/ of almost 100% is obtained shortly after the rf turn on, but the efficiency drops to typically 5-10% after this initial transient which dies away in about 50ms. The cut-off density for electron tail formation was also investigated. It correlated with the onset of parametric decay and ion tail formation near the plasma edge. However, at high magnetic fields and high plasma currents (B = 10T, l/sub p/ = 0.5MA, H plasma) an ion tail was observed even below the parametric threshold density

  8. Measurement of electrical current density distribution in a simple head phantom with magnetic resonance imaging

    International Nuclear Information System (INIS)

    Knowledge of the influence of the human skull on the electrical current (d.c.) distribution within the brain tissue could prove useful in measuring impedance changes inside the human head. These changes can be related to physiological functions. The studies presented in this paper examine the current density distribution in a simple phantom consisting of a saline filled tank (to simulate scalp and brain) and a ring made of dental grade plaster of Paris (to simulate the human skull). Images of the distribution of the d.c. density of the phantom with and without the plaster of Paris ring were produced using a magnetic resonance imaging technique. These images indicate that the skull is likely to produce a more uniform d.c. density within the brain. (author)

  9. Low-field critical current density in porous MgB2 powders

    Science.gov (United States)

    Agassi, Y. D.

    2013-09-01

    Porous MgB2 powders are comprised of an ensemble of irregularly shaped constituents. In this work we introduce a model for the critical current density in such powders in the presence of a low external field H (H effects of vortex-lattice elasticity can be neglected and vortex pinning takes place within the powder-constituents. The ensuing critical current-density expression is a product of three decoupled factors: The first sets the scale for the critical current-density magnitude, while the second and third factors contain the field and powder-constituent size-parameters dependencies, respectively. The field dependent factor is of the form H-n and 0.5⩽n⩽1.0, where the limiting exponents n = 0.5 and n = 1.0 correspond to vortex configurations within a powder-constituent of a linear array and a two-dimensional lattice, respectively. For the calculations, we assume for the powder constituent shape a cylinder of arbitrary height and radius, where an external field and a single pinned vortex are aligned in parallel to the cylinder’s axis. The exact fields of this configuration are derived. The size-parameters dependence implies enhanced critical current density for a cigar-like shape powder-constituent aligned with the field, and of radius smaller than about three times the penetration depth. These conclusions are consistent with pertaining data.

  10. Importance of spacing in the development of high current densities in multifilamentary superconductors

    International Nuclear Information System (INIS)

    It has been shown that by reducing the spacing between the filaments and keeping all the other factors the same, significant increases in current density can be achieved in conventional multifilamentary Nb-Ti superconductors of the type used in the Colliding Beam Accelerator and Tevatron dipole magnet designs. (author)

  11. On the propagation of a gravity current into a fluid with horizontal and vertical density gradient

    Science.gov (United States)

    Pham, Hieu; Sarkar, Sutanu

    2015-11-01

    Large-eddy simulations are used to investigate the dynamics of a rotating gravity current propagating in the ocean surface mixed layer on top of a pycnocline. Two simulations with different conditions in the surface mixed layer are performed: one with a homogenous mixed layer and one with a horizontal density gradient. In the latter case, the density in the mixed layer decreases with propagating distance. In both cases, a nonlinear bore forms at the front of the gravity current with Kelvin-Helmholtz billows that develop below and in the region behind the bore. In the case with a homogeneous mixed layer, the bore propagates at a constant speed which is proportional to √{g' H } where g' is the reduced gravity and H is the mixed layer depth. In the case with the horizontal gradient, the speed decreases in time. It is found that the horizontal density gradient influences the propagation of the bore in the following ways: (1) It reduces the buoyancy difference which drives the bore; (2) It generates a horizontal pressure gradient which drives a counter gravity current opposing the bore. The counter current creates a flow-converging zone ahead of the bore. The speed of the bore is found be dependent of the horizontal density gradient and the traveling distance of the bore.

  12. Simulation of Space Charge Effects in Electron Optical System Based on the Calculations of Current Density

    Czech Academy of Sciences Publication Activity Database

    Zelinka, Jiří; Oral, Martin; Radlička, Tomáš

    2015-01-01

    Roč. 21, S4 (2015), s. 246-251. ISSN 1431-9276 R&D Projects: GA MŠk(CZ) LO1212 Institutional support: RVO:68081731 Keywords : electron optical system * calculations of current density Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.877, year: 2014

  13. Simulation of space charge effects in electron optical systems based on the calculation of current density

    Czech Academy of Sciences Publication Activity Database

    Zelinka, Jiří; Oral, Martin; Radlička, Tomáš

    Brno: Institute of Scientific Instruments AS CR, v. v. i, 2014. s. 91. ISBN 978-80-87441-11-4. [International Conference on Charged Parrticle Optics /9./. 31.08.2014-05.09.2014, Brno] Institutional support: RVO:68081731 Keywords : space charge * current density evaluation * self-consistent computation * remeshing * FEM Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  14. Efficient algorithm for current spectral density calculation in single-electron tunneling and hopping

    OpenAIRE

    Sverdlov, Viktor A.; Kinkhabwala, Yusuf A.; Korotkov, Alexander N.

    2005-01-01

    This write-up describes an efficient numerical method for the Monte Carlo calculation of the spectral density of current in the multi-junction single-electron devices and hopping structures. In future we plan to expand this write-up into a full-size paper.

  15. Pair-Breaking Critical Current Density of Two-Band Superconductor MgB2

    Institute of Scientific and Technical Information of China (English)

    I.N. Askerzade

    2005-01-01

    Temperature dependence of the pair-breaking critical current density of MgB2, jd(T), is studied using a two-band Ginzburg-Landau theory. The results are shown to be in good agreement with experimental data for the superconducting magnesium diboride MgB2.

  16. Zinc electrodes for alkaline reserve cells. [German patent; Ag oxide cathode

    Energy Technology Data Exchange (ETDEWEB)

    Lala, A.

    1977-01-20

    Higher current densities at lower operational temperatures can be obtained from alkaline filler elements with silver oxide cathodes if according to the invention a foil or net each of aluminium or aluminium alloy lies on both sides of the current tap of the anode and a zinc foil each on the electrolyte side.

  17. Emissivity of a multibeam electron gun with a glassy carbon field-emission cathode

    Science.gov (United States)

    Bushuev, N. A.; Glukhova, O. E.; Grigor'ev, Yu. A.; Ivanov, D. V.; Kolesnikova, A. S.; Nikolaev, A. A.; Shalaev, P. D.; Shesterkin, V. I.

    2016-02-01

    A multibeam triode electron gun with a glassy carbon field-emission cathode that is intended for an O-type microwave amplifier is studied. The electric field strength and the current density at the microtips versus the distance to the center of a cell of the cathode-grid unit are calculated. Calculation data are compared with experimental results. It is shown that about 70% of the cathode current in each cell is accounted for by microtips arranged in a circumferential ring no wider than 20 μm. The field-emission current density inside the ring exceeds 40 A/cm2, and the current per microtip equals 43.1 μA.

  18. Transport, deposition, and liftoff in laboratory density currents composed of hot particles in air

    Science.gov (United States)

    Andrews, B. J.; Manga, M.

    2010-12-01

    Understanding the dynamics of transport, deposition, and air entrainment in pyroclastic density currents (PDCs) is required for accurate predictions of future current behaviors and interpretations of ancient deposits, but directly observing the interiors of natural PDCs is effectively impossible. We model PDCs with scaled, hot, particle-laden density currents generated in a 6 m long, 0.6 m wide, 1.8 m tall air-filled tank. Comparison of relevant scaling between our experiments and natural PDCs indicates that we are accurately capturing much of the dynamics of dilute PDCs: * Reynolds numbers of our experiments are lower than natural currents, 10^3 compared to 10^6, but still fully turbulent; * Densimetric and Thermal Richardson numbers are of O(1) in both natural and modeled currents; * Stokes and settling numbers for particles in the experiments fall within the expected range for natural PDCs. Conditions within the tank are monitored with temperature and humidity probes. Experiments are illuminated with sheet lighting, and recorded with high-definition video cameras. In general, currents have average velocities of 10-20 cm/s, initial thicknesses of 10-20 cm (although thickness greatly increases as currents entrain and expand air), and run out or lift off distances of 3-5 m. Large Kelvin-Helmholtz type eddies usually form along the top of the current immediately behind the head; these vortices are similar in size to the total current thickness. In currents that lift off, the distal current end typically retreats with time. Preliminary results suggest that lift off distance decreases with increasing thermal Richardson number. Analysis of turbulent structures indicates that the current heads are dominated by large coherent structures with length scales, L, comparable to the current thickness. Within 5-10 L of the current fronts, sequences of similar large eddies often occur. At greater distances behind the current fronts, turbulent structures become smaller and less

  19. A study on current density distribution reproduction by bounded-eigenfunction expansion for a tokamak plasma

    International Nuclear Information System (INIS)

    Plasma current density distribution is one of the most important controlled variables to determine plasma performance of energy confinement and stability in a tokamak. However, its reproduction by using magnetic measurements solely is recognized to yield an ill-posed problem. A method to presume the formulas giving profiles of plasma pressure and current has been adopted to regularize the ill-posedness, and hence it has been reported the current density distribution can be reproduced as a solution of Grad-Shafranov equation within a certain accuracy. In order to investigate its strict reproducibility from magnetic measurements in this inverse problem, a new method of 'bounded-eigenfunction expansion' is introduced, and it was found that the reproducibility directly corresponds to the independence of a series of the special function. The results from various investigations in an aspect of applied mathematics concerning this inverse problem are presented in detail. (author)

  20. Critical current density in thin superconducting TaN film structures

    International Nuclear Information System (INIS)

    The critical current density jC in thin TaN film single-bridge structures with different width from 60 nm to 8 μm has been studied in a wide temperature range from 4.2 K up to TC ≈ 10.2 K. At T → TC, the jC(T) curves of all bridges are described by the temperature dependence of the Ginzburg-Landau de-paring critical current in a temperature range increasing with the decrease in width of the bridges. However the zero-temperature value of the critical current density jCexp(0) used as fitting parameter decreases monotonically with the decrease in width of the bridges below ≈1 μm.

  1. Real critical current density and material power law of YBa2Cu3O7-δ

    International Nuclear Information System (INIS)

    The current-voltage characteristics have been measured on a YBa2Cu3O7-δ epitaxial thin film. Using a material power law, we determine the temperature and field dependencies of the characteristic pinning potential UJ and the real critical current density Jc at different fields and temperatures. It is shown that Jc is completely different from the conventional critical current density JE, which is determined by the electronic-field criterion. Thus, the time-honoured electronic-field criterion is no longer reasonable for high-Tc superconductors. By further investigation of the results of Jc and UJ, we are able to present a physical picture of the transformation of the pinning potential well with increasing temperature and hence determine the transition point from vortex-glass phase to vortex-liquid phase. Copyright (2000) CSIRO Australia

  2. High temperature and current density induced degradation of multi-layer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Baoming; Haque, M. A., E-mail: mah37@psu.edu [Mechanical and Nuclear Engineering, The Pennsylvania State University, 314, Leonhard Building, University Park, Pennsylvania 16802 (United States); Mag-isa, Alexander E.; Kim, Jae-Hyun [Korea Institute of Machinery and Materials, 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Lee, Hak-Joo [Korea Institute of Machinery and Materials, 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of); Center for Advanced Meta-Materials (CAMM), 156 Gajungbuk-ro, Yuseong-gu, Daejeon 305-343 (Korea, Republic of)

    2015-10-19

    We present evidence of moderate current density, when accompanied with high temperature, promoting migration of foreign atoms on the surface of multi-layer graphene. Our in situ transmission electron microscope experiments show migration of silicon atoms at temperatures above 800 °C and current density around 4.2 × 10{sup 7} A/cm{sup 2}. Originating from the micro-machined silicon structures that clamp the freestanding specimen, the atoms are observed to react with the carbon atoms in the multi-layer graphene to produce silicon carbide at temperatures of 900–1000 °C. In the absence of electrical current, there is no migration of silicon and only pyrolysis of polymeric residue is observed.

  3. Influence of the Iron Anisothermal Sintering on the Characteristic of the Hollow Cathode Discharge

    Institute of Scientific and Technical Information of China (English)

    BRUNATTO; Silvio Francisco; MUZART; Joel Louis Rene

    2004-01-01

    This work studies the influence of anisothermal iron sintering process on hollow cathode discharge characteristics. Two independent cathodes form an annular discharge. The pressed cylindrical iron powder sample, acting as central cathode, was placed concentrically in the interior of an external cathode. The external cathode, machined from an AISI 3 l0 steel bar, besides acting to confine the geometry of the plasma, can also acts as a source of alloying elements. The sample heating is a function of the ion bombardment energy and, so, of the discharge electrical parameters: current (or current density) and the effective potential applied to the cathode. Successive anisothermal sintering is performed in a same sample until the reproducibility of the electrical parameters being obtained. The heating experiments up to 1250 ℃, in a gas mixture of 80% Ar + 20% H2, at pressure of 133 Pa, at flow of 2xl0-6 m3s-1, with an inter-cathode radial space of 5.8 mm,were carried out. It was verified the metallurgical evolution of the iron sample sintering process influences the current-ton(time switched-on of the pulse) characteristics of the discharge.

  4. Characterization of scandia doped pressed cathode fabricated by spray drying method

    International Nuclear Information System (INIS)

    Scandia doped pressed cathode was prepared by a new method of spray drying combined with two-step hydrogen reduction process. The Sc2O3 and barium-calcium aluminate co-doped powders have sub-micrometer size in the range of 0.1-1 μm and scandium oxide and barium-calcium aluminate are distributed evenly in the powders. The cathodes sintered by powder metallurgy at 1600 deg. Cb have a smooth surface and sub-micrometer grain structure with homogeneous distribution of scandium, barium, calcium and aluminum which are dispersed over and among the tungsten grains. This cathode has good emission, e.g., the current density of this cathode reaches 31.50 A/cm2 at 850 deg. Cb. After proper activation, the cathode surface is covered by a Ba-Sc-O active substances layer with a preferable atomic ratio, leading to its good emission property. The evaporation activation energy of SDP cathode with 4.58 eV is the highest among the Ba-W, M-type and SDP cathodes, and the average evaporation velocity vt of SDP cathode with 1.28 x 10-8 g cm-2 s-1 at 1150 deg. Cb is the lowest one.

  5. Influence of NaCl on Cathode Performance of Solid Oxide Fuel Cells

    Institute of Scientific and Technical Information of China (English)

    LIU Run-ru; WANG De-jun; LENG Jing

    2013-01-01

    Degradation induced by sodium chloride in air was investigated for (La0.8Sr0.2)0.98MnO3(LSM) and La0.6Sr0.4Co0.2Fe0.8O3(LSCF) cathodes in solid oxide fuel cells(SOFC).Cell performance was measured by volatilizing NaCl to be supplied to the cathode at a constant current density of 200 mA/cm2 for up to 100 h.At 800 ℃,an exposure of the cathode to 30 mg/L NaCl caused negligible degradation of LSM at least for 100 h.Slight change in the composition of the cathode materials was observed which may imply the gradual degradation of cell performance for the long-term.In addition,cell performance degradation was compared between 700 ℃ and 900 ℃,being poisoned by 30 mg/L NaC1.Degradation was negligible for LSM cathode,while LSCF cathode showed slightly poor tolerance at 700 ℃ due to the decomposition of the cathode material.Further studies should be done to clarify the long-term influence of NaCl on cathode performance.

  6. Relationship between columnar crystal spacing and electric current density in unidirectional solidification of monophase Cu-Al alloy

    Institute of Scientific and Technical Information of China (English)

    常国威; 曹丽云; 袁军平; 王自东; 吴春京; 胡汉起

    2002-01-01

    On the basis of previous theoretical inferential relationship between the columnar crystal spacing and the density of electric current applied during unidirectional solidification, the effect of current density on the columnar crystal spacing was discussed and analyzed, and the experiment was made to verify the theoretical relationship. The results show that at fast solidification speed the columnar crystal spacing decreases with increasing the density of electric current, while at slow solidification speed the columnar crystal spacing increases with increasing the density of electric current. The critical conditions for the evolution of columnar crystal spacing were confirmed. The calculated values concerning the spacing and the density are consistent with the experimental results.

  7. Cathode power distribution system and method of using the same for power distribution

    Energy Technology Data Exchange (ETDEWEB)

    Williamson, Mark A; Wiedmeyer, Stanley G; Koehl, Eugene R; Bailey, James L; Willit, James L; Barnes, Laurel A; Blaskovitz, Robert J

    2014-11-11

    Embodiments include a cathode power distribution system and/or method of using the same for power distribution. The cathode power distribution system includes a plurality of cathode assemblies. Each cathode assembly of the plurality of cathode assemblies includes a plurality of cathode rods. The system also includes a plurality of bus bars configured to distribute current to each of the plurality of cathode assemblies. The plurality of bus bars include a first bus bar configured to distribute the current to first ends of the plurality of cathode assemblies and a second bus bar configured to distribute the current to second ends of the plurality of cathode assemblies.

  8. Construction of cathode thermometry and emission test system

    International Nuclear Information System (INIS)

    A thermal cathode (Eimac Y-845) is used for an electron gun at the SPring-8 1-GeV linac. The gun can eject a 180 keV beam of 3 A from the cathode operated at a nominal heater voltage. As the discharge rate between the cathode and the grid becomes high along with the cathode driving time, we replace a cathode with a new one once a year. Before the cathode installation, we have definitely inspected new cathodes by means of a microscope to find defects in their cathodes and grids. However, the emission currents have been sometimes insufficient, or the cathode planes have contacted with the grids due to the heat distortion of the grids. We have suspected that the inadequate cathode temperature may have caused these cathode failures. To monitor the accurate cathode temperature and to reduce the cathode failures, we have constructed a measuring system of the cathode temperatures and the cathode emission currents at the test stand. We redesigned the whenelt and the anode to achieve a space-charge-limited current of 3 A at an acceleration voltage less than -70 kV. The cathode temperature at the nominal heater voltage is expected to be 854degC according to the Richardson-Dushman equation, whereas the actual temperature measured by an infrared thermometer was 813±5degC. This large disagreement is under investigation. (author)

  9. An interchangeable-cathode vacuum arc plasma source

    International Nuclear Information System (INIS)

    A simplified vacuum arc design [based on metal vapor vacuum arc (MeVVA) concepts] is employed as a plasma source for a study of a 7Be non-neutral plasma. The design includes a mechanism for interchanging the cathode source. Testing of the plasma source showed that it is capable of producing on the order of 1012 charges at confinable energies using a boron-carbide disk as the cathode target. The design is simplified from typical designs for lower energy and lower density applications by using only the trigger spark rather than the full vacuum arc in high current ion beam designs. The interchangeability of the cathode design gives the source the ability to replace only the source sample, simplifying use of radioactive materials in the plasma source. The sample can also be replaced with a completely different conductive material. The design can be easily modified for use in other plasma confinement or full MeVVA applications.

  10. Microwave generation from an axially extracted virtual cathode oscillator with a guide magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Kostov, K.G.; Nikolov, N.A. (Department of General Physics, Sofia University, Sofia 1126 (Bulgaria))

    1994-04-01

    The operation of a virtual cathode oscillator (vircator) with strong axial magnetic field has been experimentally studied. Depending on the cathode--anode gap and cathode diameter, the operating voltage varies from 200 kV up to 480 kV with 2--7 kA diode current. Microwave emission is produced by the oscillating virtual cathode. The central microwave frequency follows the beam plasma frequency. It varies by 11.5 GHz up to 22 GHz, depending on the current density. The oscillation frequency does not depend on the guide magnetic field magnitude. A maximal output power of 15[plus minus]5 MW in asymmetric transverse magnetic (TM) modes is achieved by the axially extracted vircator. Variation of the magnetic field intensity in a range of 0--40 kG has an insignificant effect upon the emitted microwave power. An electron beam power to microwave power conversion efficiency of approximately 1% is obtained.

  11. Microwave generation from an axially extracted virtual cathode oscillator with a guide magnetic field

    International Nuclear Information System (INIS)

    The operation of a virtual cathode oscillator (vircator) with strong axial magnetic field has been experimentally studied. Depending on the cathode--anode gap and cathode diameter, the operating voltage varies from 200 kV up to 480 kV with 2--7 kA diode current. Microwave emission is produced by the oscillating virtual cathode. The central microwave frequency follows the beam plasma frequency. It varies by 11.5 GHz up to 22 GHz, depending on the current density. The oscillation frequency does not depend on the guide magnetic field magnitude. A maximal output power of 15±5 MW in asymmetric transverse magnetic (TM) modes is achieved by the axially extracted vircator. Variation of the magnetic field intensity in a range of 0--40 kG has an insignificant effect upon the emitted microwave power. An electron beam power to microwave power conversion efficiency of approximately 1% is obtained

  12. Reduction of promethium on a mercury cathode

    International Nuclear Information System (INIS)

    The authors observed the separation of radioactive promethium on a mercury cathode with samarium, which showed that it can be reduced to a bivalent state. Using radiochemically-pure Pm147, the authors made a detailed study of the influence of a series of factors on the extent to which promethium passes into an amalgam. It was shown that radioactive promethium only passes into the mercury cathode if the current is relatively dense (above 50 mA/cm2) and when rare-earth elements such as ytterbium and samarium, which have a stable bivalent state, are present in the electrolyte. Electrolytic separation of the promethium is not observable until formation of the mixed potassium and samarium amalgam. The promethium then passes into the amalgam up to 85%. When the current is denser (100 mA/cm2), a notable difference may be observed in the transition speed of the promethium and samarium. The promethium separation is mainly affected by the nature of the alkali metal contained in the electrolyte. With lithium, the degree of promethium transition does not depend on the presence of another rare-earth element or the citrate ion concentration. This confirms the occurrence of electrolytic reduction of promethium in electrolysis with a mercury cathode at high current densities. Separation of the promethium into the mercury cathode goes through the stage of its reduction to a bivalent state with formation of the amalgam with the alkali metal. The authors also studied the behaviour of cerium and erbium. From the results of this study and all the published data, the authors conclude that promethium and other elements of the cerium group can be reduced to a bivalent state under certain conditions of electrolysis. (author)

  13. Effects of glycine and current density on the mechanism of electrodeposition, composition and properties of Ni-Mn films prepared in ionic liquid

    Science.gov (United States)

    Guo, Jiacheng; Guo, Xingwu; Wang, Shaohua; Zhang, Zhicheng; Dong, Jie; Peng, Liming; Ding, Wenjiang

    2016-03-01

    The effects of glycine on the mechanism of electrodeposition of Ni-Mn alloy film prepared in ChCl-urea ionic liquid were studied in order to control the composition, microstructure and properties of the film. The cyclic voltammograms revealed that the presence of glycine in the ionic liquid can inhibit the reduction of Ni2+ ions but promote the reduction of Mn2+ ions in the cathodic scan. However, it promoted the dissolution of both Ni and Mn deposits in the ChCl-urea ionic liquids during the reverse scan. Glycine changed the mode of Ni-Mn film growth from Volmer-Weber mode into Stranski-Krastanov mode. The Mn content in the Ni-Mn film increased with the increase of concentration of glycine and current density. The Ni-Mn alloy film with 3.1 at.% Mn exhibited the lowest corrosion current density of 3 × 10-7 A/cm2 compared with other films prepared and exhibited better corrosion resistance than pure Ni film in 3.5 wt.% NaCl solution.

  14. Distribution of the Current Density in Electrolyte of the Pem Fuel Cell

    Directory of Open Access Journals (Sweden)

    Eugeniusz Kurgan

    2004-01-01

    Full Text Available In this paper water management in proton exchange membrane (PEM fuel cell is considered. Firt mass convervation law for water is applied. Next proton transport is described by the Nernst-Planck equation and liqid water convection velocity is eliminated by the Schlogl equation. Electro-osmotic drag coefficient is related to hydrogen index and experimentally determined swelling coefficient. Three partial differential equations for molar water concentration Cw, electric potential ϕ and water pressure Pw are formulated. Current density vector i is derived from proton flux expression. These equations together with adequate boundary conditions were solved using finite element method. The distribution of electric potential and current density in function of geometrical parametres is investigated. At the end some illustrative example is given.

  15. Predicting size effect on diffusion-limited current density of oxygen reduction by copper wire

    Institute of Scientific and Technical Information of China (English)

    LU Yonghong; XU Haibo; WANG Jia; ZHONG Lian

    2011-01-01

    The size effect of copper wire radius (0.04鈥?.82 mm) on the diffusion-limited current density of an oxygen reduction reaction in stagnant simulated seawater (naturally aerated 0.5 mol/L NaCl) is investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) and compared with the results obtained in 0.5 mol/L H2SO4. In the oxygen diffusion-limited range, size effect is found to occur independent of electrolytes, which is attributed to non-linear diffusion. Additionally, to satisfy application in a marine setting, an empirical equation correlating oxygen diffusion-limited current density to copper wire radius is proposed by fitting experimental data.

  16. Measurements of intergranular critical current density of high Tc sintered superconductors

    International Nuclear Information System (INIS)

    It's well known that the intergranular critical current density (Jc) depends largely on the magnetic field value because of the presence of weak links between the grains in sintered samples. This strong dependence determines some problems in Jc measurements, above all at low magnetic fields value where such dependence is even more marked. In particular: supercurrents create a self-field which may affect the uniformity of Jc values. In these conditions the measurement evidently gives a mean value of Jc, depending on the size of the sample. For magnetic field values of only a few hundred Gauss, Jc values are already so low that a high degree of measuring sensitivity is required. Lastly it is difficult to distinguish homogeneous from inhomogeneous (clusters) samples by means of ordinary inductive measurements. The aim of this paper is to propose a method of measuring intergranular critical current density which overcomes these problems

  17. High current density and low turn-on field from aligned Cd(OH)2 nanosheets

    Science.gov (United States)

    Bagal, Vivekanand S.; Patil, Girish P.; Deore, Amol B.; Baviskar, Prashant K.; Suryawanshi, Sachin R.; More, Mahendra A.; Chavan, Padmakar G.

    2016-04-01

    High current density of 9.8 mA/cm2 was drawn at an applied field of 4.1 V/μm from aligned Cd(OH)2 nanosheets and low turn-on field of 1.4 V/μm was found for the emission current density of 10 μA/cm2. The aligned Cd(OH)2 nanosheets were synthesized by CBD technique on Cadmium foil. To the best of our knowledge this is the first report on the field emission studies of Cd(OH)2 nanosheets. Simple synthesis route coupled with superior field emission properties indicate the possible use of Cd(OH)2 nanosheets for micro/nanoelectronic devices.

  18. Simulating the frontal instability of lock-exchange density currents with dissipative particle dynamics

    Science.gov (United States)

    Li, Yanggui; Geng, Xingguo; Wang, Heping; Zhuang, Xin; Ouyang, Jie

    2016-06-01

    The frontal instability of lock-exchange density currents is numerically investigated using dissipative particle dynamics (DPD) at the mesoscopic particle level. For modeling two-phase flow, the “color” repulsion model is adopted to describe binary fluids according to Rothman-Keller method. The present DPD simulation can reproduce the flow phenomena of lock-exchange density currents, including the lobe-and-cleft instability that appears at the head, as well as the formation of coherent billow structures at the interface behind the head due to the growth of Kelvin-Helmholtz instability. Furthermore, through the DPD simulation, some small-scale characteristics can be observed, which are difficult to be captured in macroscopic simulation and experiment.

  19. Morphological features of the copper surface layer under sliding with high density electric current

    Energy Technology Data Exchange (ETDEWEB)

    Fadin, V. V., E-mail: fvv@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Aleutdinova, M. I., E-mail: aleut@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); Seversk Technological Institute, Branch of State Autonomous Educational Institution of Higher Professional Education “National Research Nuclear University “MEPhI”, Seversk, 636036 (Russian Federation); Rubtsov, V. Ye., E-mail: rvy@ispms.ru [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation); Aleutdinova, V. A., E-mail: valery-aleut@yandex.ru [National Research St. Petersburg State Polytechnical University, St. Petersburg, 195251 (Russian Federation)

    2015-10-27

    Conductivity and wear intensity of copper under the influence of dry friction and electric current with contact density higher 100 A/cm{sup 2} are presented. It is shown that an increase in hardness and heat outflow from a friction zone leads to the reduction of wear intensity and current contact density increase corresponding to the beginning of catastrophic wear. Structural changes, such as the formation of FeO oxide and α-Fe particles in the copper surface layer, have also been found. It is observed that a worn surface is deformed according to a viscous liquid mechanism. Such singularity is explained in terms of appearance of high-excited atomic states in deforming micro-volumes near contact spots that lead to easy stress relaxation by local plastic shears in the vicinity of stress concentrators. In common this effect allows to achieve high wear resistance.

  20. Global Solar Free Magnetic Energy and Electric Current Density Distribution of Carrington Rotation 2124

    CERN Document Server

    Tadesse, Tilaye; Alexei, Pevtsov A; Macneice, P; Gosain, S

    2013-01-01

    Solar eruptive phenomena, like flares and coronal mass ejections(CMEs) are governed by magnetic fields. To describe the structure of these phenomena one needs information on the magnetic flux density and the electric current density vector components in three dimensions throughout the atmosphere. However, current spectro-polarimetric measurements typically limit the determination of the vector magnetic field only to the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field for global solar atmosphere using a nonlinear force-free field(NLFFF) extrapolation codes implemented to a synoptic maps of photospheric vector magnetic field synthesized from Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) as boundary condition. Using the resulting three dimensional magnetic field, we calculate the three dimensio...

  1. Morphological features of the copper surface layer under sliding with high density electric current

    International Nuclear Information System (INIS)

    Conductivity and wear intensity of copper under the influence of dry friction and electric current with contact density higher 100 A/cm2 are presented. It is shown that an increase in hardness and heat outflow from a friction zone leads to the reduction of wear intensity and current contact density increase corresponding to the beginning of catastrophic wear. Structural changes, such as the formation of FeO oxide and α-Fe particles in the copper surface layer, have also been found. It is observed that a worn surface is deformed according to a viscous liquid mechanism. Such singularity is explained in terms of appearance of high-excited atomic states in deforming micro-volumes near contact spots that lead to easy stress relaxation by local plastic shears in the vicinity of stress concentrators. In common this effect allows to achieve high wear resistance

  2. Diffusion layer characteristics for increasing the performance of activated carbon air cathodes in microbial fuel cells

    KAUST Repository

    Zhang, Xiaoyuan

    2016-01-01

    The characteristics of several different types of diffusion layers were systematically examined to improve the performance of activated carbon air cathodes used in microbial fuel cells (MFCs). A diffusion layer of carbon black and polytetrafluoroethylene (CB + PTFE) that was pressed onto a stainless steel mesh current collector achieved the highest cathode performance. This cathode also had a high oxygen mass transfer coefficient and high water pressure tolerance (>2 m), and it had the highest current densities in abiotic chronoamperometry tests compared to cathodes with other diffusion layers. In MFC tests, this cathode also produced maximum power densities (1610 ± 90 mW m−2) that were greater than those of cathodes with other diffusion layers, by 19% compared to Gore-Tex (1350 ± 20 mW m−2), 22% for a cloth wipe with PDMS (1320 ± 70 mW m−2), 45% with plain PTFE (1110 ± 20 mW m−2), and 19% higher than those of cathodes made with a Pt catalyst and a PTFE diffusion layer (1350 ± 50 mW m−2). The highly porous diffusion layer structure of the CB + PTFE had a relatively high oxygen mass transfer coefficient (1.07 × 10−3 cm s−1) which enhanced oxygen transport to the catalyst. The addition of CB enhanced cathode performance by increasing the conductivity of the diffusion layer. Oxygen mass transfer coefficient, water pressure tolerance, and the addition of conductive particles were therefore critical features for achieving higher performance AC air cathodes.

  3. Dependence of various SOL widths on plasma current and density in NSTX H-mode plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, J; Maingi, R; Boedo, J; Soukhanovskii, V A

    2009-02-12

    The dependence of various SOL widths on the line-averaged density ({ovr n}{sub e}) and plasma current (l{sub p}) for the quiescent H-mode plasmas with Type-V ELMs in the National Spherical Torus Experiment (NSTX) was investigated. It is found that the heat flux SOL width ({lambda}{sub q}), measured by the IR camera, is virtually insensitive to {ovr n}{sub e} and has a strong negative dependence on l{sub p}. This insensitivity of {lambda}{sub q} to {ovr n}{sub e} is consistent with the scaling law from JET H-mode plasmas that shows a very weak dependence on the upstream density. The electron temperature, ion saturation current density, electron density, and electron pressure decay lengths ({lambda}{sub Te}, {lambda}{sub jsat}, {lambda}{sub ne}, and {lambda}{sub pe}, respectively) measured by the probe showed that {lambda}{sub Te} and {lambda}{sub jsat} have strong negative dependence on l{sub p}, whereas {lambda}{sub ne} and {lambda}{sub pe} revealed only a little or no dependence. The dependence of {lambda}{sub Te} on l{sub p} is consistent with the scaling law in the literature while {lambda}{sub ne} and {lambda}{sub pe} dependence shows a different trend.

  4. Self-field effects upon the critical current density of flat superconducting strips

    International Nuclear Information System (INIS)

    We develop a general theory to account self-consistently for self-field effects upon the average transport critical current density Jc of a flat type-II superconducting strip in the mixed state when the bulk pinning is characterized by a field-dependent depinning critical current density Jp(B), where B is the local magnetic flux density. We first consider the possibility of both bulk and edge-pinning contributions but conclude that bulk pinning dominates over geometrical edge-barrier effects in state-of-the-art YBCO films and prototype second-generation coated conductors. We apply our theory using the Kim model, JpK(B) = JpK(0)/(1+ vertical bar B vertical bar/B0), as an example. We calculate Jc(Ba) as a function of a perpendicular applied magnetic induction Ba and show how Jc(Ba) is related to JpK(B). We find that Jc(Ba) is very nearly equal to JpK(Ba) when Ba≥Ba*, where Ba* is the value of Ba that makes the net flux density zero at the strip's edge. However, Jc(Ba) is suppressed relative to JpK(Ba) at low fields when Baa*, with the largest suppression occurring when Ba*/B0 is of order unity or larger

  5. Current Density Functional Theory Using Meta-Generalized Gradient Exchange-Correlation Functionals.

    Science.gov (United States)

    Furness, James W; Verbeke, Joachim; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

    2015-09-01

    We present the self-consistent implementation of current-dependent (hybrid) meta-generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn-Sham current density functional theory (KS-CDFT). A unique feature of the nonperturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 au (∼235 kT) in strength. CDFT functionals based on the TPSS and B98 forms are investigated, and their performance is assessed by comparison with accurate coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) data. In the weak field regime, magnetic properties such as magnetizabilities and nuclear magnetic resonance shielding constants show modest but systematic improvements over generalized gradient approximations (GGA). However, in the strong field regime, the mGGA-based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T) data. In contrast to functionals based on the vorticity, these forms are found to be numerically stable, and their accuracy at high field suggests that the extension of mGGAs to CDFT via the generalized kinetic energy density should provide a useful starting point for further development of CDFT approximations. PMID:26575912

  6. Magnetic structure of nickel nanowires after the high-density current pulse

    Science.gov (United States)

    Nurgazizov, N. I.; Bizyaev, D. A.; Bukharaev, A. A.

    2016-05-01

    Changes in the magnetic structure of nickel nanowires formed on a nonconductive surface after the high-density current pulse have been investigated using magnetic force microscopy and voltammetry. Based on the obtained experimental data and results of the computer simulation, it has been concluded that the main reason for the change in the magnetic structure is the heating of the nanowire by a current pulse. It has been shown that, during the subsequent cooling, the newly formed magnetic structure is pinned by surface roughnesses of the relief of the nanowire under investigation.

  7. Current density and poloidal magnetic field for toroidal elliptic plasmas with triangularity

    International Nuclear Information System (INIS)

    Changes in the poloidal magnetic field around a tokamak magnetic surface due to different values of triangularity and ellipticity are analyzed in this paper. The treatment here presented allows the determination of the poloidal magnetic field from knowledge of the toroidal current density. Different profiles of these currents are studied. Improvements in the analytic forms of the magnetic surfaces have also been found. The treatment has been performed using a recent published system of coordinates. Suitable analytic equations have been used for the elliptic magnetic surfaces with triangularity and Shafranov shift

  8. Temperature dependence of current density and admittance in metal-insulator-semiconductor junctions with molecular insulator

    OpenAIRE

    Fadjie-Djomkam, Alain-Bruno; Ababou-Girard, Soraya; Hiremath, R.; Herrier, Cyril; Fabre, Bruno; Solal, Francine; Godet, Christian

    2011-01-01

    Electrical transport in ultrathin Metal-insulator-semiconductor (MIS) tunnel junctions is analyzed using the temperature dependence of current density and admittance characteristics, as illustrated by Hg//C12H25 - n Si junctions incorporating n-alkyl molecular layers (1.45 nm thick) covalently bonded to Si(111). The voltage partition is obtained from J(V, T) characteristics, over eight decades in current. In the low forward bias regime (0.2-0.4 V) governed by thermionic emission, the observed...

  9. Defects influence on short circuit current density in p-i-n silicon solar cell

    International Nuclear Information System (INIS)

    The admittance analysis method has been used to calculate the collection efficiency and the short circuit current density in a-Si:H p-i-n solar cell, as a function of the thickness of i-layer. Its is evident that the results of the short circuit current can be used to determine the optimal thickness of the i-layer of a cell, and it will be more accurate in comparison with the previous studies using a constant generation rate or an empirical exponential function for the generation of charge carriers throughout the i-layer

  10. 4H-SiC junction-barrier Schottky diodes with high forward current densities

    Science.gov (United States)

    Tone, Kiyoshi; Zhao, Jian H.; Weiner, Maurice; Pan, Menghan

    2001-07-01

    4H-SiC junction-barrier Schottky (JBS) diodes blocking 1000 V have been fabricated. I-V characteristics have been evaluated at room temperature and 255 °C in comparison with the Schottky barrier (SB) and pin diodes fabricated on the same wafer. While the low reverse leakage confirms the functioning of JBS, the high forward current densities of 630 and 210 A cm-2 at 4.0 V at room temperature and 255 °C, respectively, with only ~20% reduction from those of the SB diodes, clearly demonstrate that the SiC JBS diodes can be fabricated with acceptable sacrifice in the forward current capacities.

  11. Structural transitions in electron beam deposited Co–carbonyl suspended nanowires at high electrical current densities

    Directory of Open Access Journals (Sweden)

    Gian Carlo Gazzadi

    2015-06-01

    Full Text Available Suspended nanowires (SNWs have been deposited from Co–carbonyl precursor (Co2(CO8 by focused electron beam induced deposition (FEBID. The SNWs dimensions are about 30–50 nm in diameter and 600–850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC and hexagonal close-packed (HCP Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM analysis and by energy-dispersive X-ray (EDX spectroscopy, respectively. Current (I–voltage (V measurements with current densities up to 107 A/cm2 determine different structural transitions in the SNWs, depending on the I–V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 107 A/cm2. The role played by resistive heating and electromigration in these transitions is discussed.

  12. Structural transitions in electron beam deposited Co-carbonyl suspended nanowires at high electrical current densities.

    Science.gov (United States)

    Gazzadi, Gian Carlo; Frabboni, Stefano

    2015-01-01

    Suspended nanowires (SNWs) have been deposited from Co-carbonyl precursor (Co2(CO)8) by focused electron beam induced deposition (FEBID). The SNWs dimensions are about 30-50 nm in diameter and 600-850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC) and hexagonal close-packed (HCP) Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM) analysis and by energy-dispersive X-ray (EDX) spectroscopy, respectively. Current (I)-voltage (V) measurements with current densities up to 10(7) A/cm(2) determine different structural transitions in the SNWs, depending on the I-V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 10(7) A/cm(2). The role played by resistive heating and electromigration in these transitions is discussed. PMID:26199833

  13. Magnetic resonance electrical impedance tomography (MREIT): conductivity and current density imaging

    International Nuclear Information System (INIS)

    This paper reviews the latest impedance imaging technique called Magnetic Resonance Electrical Impedance Tomography (MREIT) providing information on electrical conductivity and current density distributions inside an electrically conducting domain such as the human body. The motivation for this research is explained by discussing conductivity changes related with physiological and pathological events, electromagnetic source imaging and electromagnetic stimulations. We briefly summarize the related technique of Electrical Impedance Tomography (EIT) that deals with cross-sectional image reconstructions of conductivity distributions from boundary measurements of current-voltage data. Noting that EIT suffers from the ill-posed nature of the corresponding inverse problem, we introduce MREIT as a new conductivity imaging modality providing images with better spatial resolution and accuracy. MREIT utilizes internal information on the induced magnetic field in addition to the boundary current-voltage measurements to produce three-dimensional images of conductivity and current density distributions. Mathematical theory, algorithms, and experimental methods of current MREIT research are described. With numerous potential applications in mind, future research directions in MREIT are proposed

  14. Internally oxidized Nb₃Sn strands with fine grain size and high critical current density.

    Science.gov (United States)

    Xu, Xingchen; Sumption, Michael D; Peng, Xuan

    2015-02-25

    Nb3Sn strands fabricated using Nb-Zr alloy can be internally oxidized, provided that oxygen is properly supplied via an oxide powder. This allows the formation of fine intragranular and intergranular ZrO2 particles in a Nb3Sn matrix. These particles can refine the grain size by a factor of three and thereby greatly enhance the Nb3Sn critical current density. PMID:25582555

  15. Accurate Prediction of Transimpedances and Equivalent Input Noise Current Densities of Tuned Optical Receiver Front Ends

    DEFF Research Database (Denmark)

    Liu, Qing Zhong

    Novel analytical expressions have been derived for calculating transimpedances and equivalent input noise current densities of five tuned optical receiver front ends based on PIN diode and MESFETs or HEMTs. Miller's capacitance, which has been omitted in previous studies, has been taken into...... account. The accuracy of the expressions has been verified by using Touchstone simulator. The agreement between the calculated and simulated front end performances is very good....

  16. Occupation probabilities and current densities of bulk and edge states of a Floquet topological insulator

    Science.gov (United States)

    Dehghani, Hossein; Mitra, Aditi

    2016-05-01

    Results are presented for the occupation probabilities and current densities of bulk and edge states of half-filled graphene in a cylindrical geometry and irradiated by a circularly polarized laser. It is assumed that the system is closed and that the laser has been switched on as a quench. Laser parameters corresponding to some representative topological phases are studied: one where the Chern number of the Floquet bands equals the number of chiral edge modes, a second where anomalous edge states appear in the Floquet Brillouin zone boundaries, and a third where the Chern number is zero, yet topological edge states appear at the center and boundaries of the Floquet Brillouin zone. Qualitative differences are found for the high-frequency off-resonant and low-frequency on-resonant laser with edge states arising due to resonant processes occupied with a high effective temperature on the one hand, while edge states arising due to off-resonant processes occupied with a low effective temperature on the other. For an ideal half-filled system where only one of the bands in the Floquet Brillouin zone is occupied and the other empty, particle-hole and inversion symmetry of the Floquet Hamiltonian implies zero current density. However the laser switch-on protocol breaks the inversion symmetry, resulting in a net cylindrical sheet of current density at steady state. Due to the underlying chirality of the system, this current density profile is associated with a net charge imbalance between the top and bottom of the cylinders.

  17. Contactless estimation of critical current density and its temperature dependence using magnetic measurements

    Czech Academy of Sciences Publication Activity Database

    Youssef, A.; Baničová, L.; Švindrych, Zdeněk; Janů, Zdeněk

    2010-01-01

    Roč. 118, č. 5 (2010), s. 1036-1037. ISSN 0587-4246. [Czech and Slovak Conference on Magnetism /14./. Košice, 06.07.2010-09.07.2010] R&D Projects: GA MŠk(CZ) ME10069 Institutional research plan: CEZ:AV0Z10100520 Keywords : superconductivity * critical state * Bean model * critical current density Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.467, year: 2010

  18. Measurement of current density distribution in shaped e-beam writers

    Czech Academy of Sciences Publication Activity Database

    Horáček, Miroslav; Bok, Jan; Kolařík, Vladimír; Urbánek, Michal; Matějka, Milan; Krátký, Stanislav

    Praha: Czechoslovak Microscopy Society, 2014. ISBN 978-80-260-6720-7. [International Microscopy Congres /18./. Praha (CZ), 07.09.2014-12.09.2014] R&D Projects: GA MŠk(CZ) LO1212; GA MŠk ED0017/01/01; GA TA ČR TE01020118 Institutional support: RVO:68081731 Keywords : e-beam writer * current density Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering

  19. Low-field critical current density in porous MgB{sub 2} powders

    Energy Technology Data Exchange (ETDEWEB)

    Agassi, Y.D., E-mail: yehoshua.agassi@navy.mil

    2013-09-15

    Highlights: • Porosity of MgB{sub 2} wires suggests that vortex pinning occurs within agglomerates of MgB{sub 2} grains. • Based on the London equation, the exact fields of a vortex in a superconductor cylinder are derived. • The calculated critical current field dependence is H{sup -n}, 0.5⩽n⩽1.0. • The calculated critical current dependence on size parameters is consistent with data. -- Abstract: Porous MgB{sub 2} powders are comprised of an ensemble of irregularly shaped constituents. In this work we introduce a model for the critical current density in such powders in the presence of a low external field H (H < 4 T) and in the high-porosity limit, where effects of vortex-lattice elasticity can be neglected and vortex pinning takes place within the powder-constituents. The ensuing critical current–density expression is a product of three decoupled factors: The first sets the scale for the critical current–density magnitude, while the second and third factors contain the field and powder-constituent size-parameters dependencies, respectively. The field dependent factor is of the form H{sup −n} and 0.5⩽n⩽1.0, where the limiting exponents n = 0.5 and n = 1.0 correspond to vortex configurations within a powder-constituent of a linear array and a two-dimensional lattice, respectively. For the calculations, we assume for the powder constituent shape a cylinder of arbitrary height and radius, where an external field and a single pinned vortex are aligned in parallel to the cylinder’s axis. The exact fields of this configuration are derived. The size-parameters dependence implies enhanced critical current density for a cigar-like shape powder-constituent aligned with the field, and of radius smaller than about three times the penetration depth. These conclusions are consistent with pertaining data.

  20. Modeling of the current density distribution under surface posterior-tibial-nerve electric stimulator

    OpenAIRE

    Wong, YW; Leong, JCY; Yu, J.; Luk, KDK; Hu, Y.; Lu, WW

    1998-01-01

    Stimulation of the posterior tibial nerve is commonly used in the measurement of somatosensory evoked potential (SEP). To improve the efficiency of stimulation, the potential field and current density distributions under the surface electrodes were modeled and simulated. In our model, three layers were assumed: (1) the air environment, (2) electrode and paste (3) human body (skin and soft tissues). The mirror method was used to analyze the potential field of point charge. Integration of the f...

  1. Higher critical current density achieved in Bi-2223 High-Tc superconductors

    OpenAIRE

    M. S. Shalaby; H.M. Hashem; T.R. Hammad; L.A. Wahab; K.H. Marzouk; Soltan, S.

    2016-01-01

    Bi2Sr2Ca2Cu3Ox (Bi-2223) were prepared using a solid state reaction method at different sintering times and temperatures. Structural phase identifications have been done using X-Ray analysis and refinement by Reitveld method which proves the coexistence of Bi-2223 and Bi-2212 phases. The critical transition temperature Tc and critical current density Jc values were measured using superconducting quantum interference device magnetometer (SQUID) and by the magneto-optics technique. A remarkable...

  2. PERFORMANCE OPTIMIZATION OF LINEAR INDUCTION MOTOR BY EDDY CURRENT AND FLUX DENSITY DISTRIBUTION ANALYSIS

    OpenAIRE

    M. S. MANNA; Marwaha, S.; MARWAHA A.

    2011-01-01

    The development of electromagnetic devices as machines, transformers, heating devices confronts the engineers with several problems. For the design of an optimized geometry and the prediction of the operational behaviour an accurate knowledge of the dependencies of the field quantities inside the magnetic circuits is necessary. This paper provides the eddy current and core flux density distribution analysis in linear induction motor. Magnetic flux in the air gap of the Linear Induction Motor ...

  3. Enhanced current and power density of micro-scale microbial fuel cells with ultramicroelectrode anodes

    Science.gov (United States)

    Ren, Hao; Rangaswami, Sriram; Lee, Hyung-Sool; Chae, Junseok

    2016-09-01

    We present a micro-scale microbial fuel cell (MFC) with an ultramicroelectrode (UME) anode, with the aim of creating a miniaturized high-current/power-density converter using carbon-neutral and renewable energy sources. Micro-scale MFCs have been studied for more than a decade, yet their current and power densities are still an order of magnitude lower than those of their macro-scale counterparts. In order to enhance the current/power densities, we engineer a concentric ring-shaped UME, with a width of 20 μm, to facilitate the diffusion of ions in the vicinity of the micro-organisms that form biofilm on the UME. The biofilm extends approximately 15 μm from the edge of the UME, suggesting the effective biofilm area increases. Measured current/power densities per the effective area and the original anode area are 7.08  ±  0.01 A m‑2 & 3.09  ±  0.04 W m‑2 and 17.7  ±  0.03 A m‑2 & 7.72  ±  0.09 W m‑2, respectively. This is substantially higher than any prior work in micro-scale MFCs, and very close, or even higher, to that of macro-scale MFCs. A Coulombic efficiency, a measure of how efficiently an MFC harvests electrons from donor substrate, of 70%, and an energy conversion efficiency of 17% are marked, highlighting the micro-scale MFC as an attractive alternative within the existing energy conversion portfolio.

  4. Further improvements in current density by reduction of filament spacing in multifilamentary Nb-Ti superconductors

    International Nuclear Information System (INIS)

    Current densities, Jsub(c)s, approaching those required in the dipole magnets of the Superconducting Super Collider have been achieved in conventional multifilamentary Nb-Ti superconductors of the type used in the Colliding Beam Accelerator and the Tevatron magnet designs. These high Jsub(c)s have resulted from a simple reduction in the spacing-to-diameter ratio, S/D, from 0.35 to 0.13, keeping other factors the same. (author)

  5. Determination of critical current density in melt-processed HTS bulks from levitation force measurements

    OpenAIRE

    Kordyuk, A. A.; Nemoshkalenko, V.V.; Viznichenko, R. V.; Habisreuther, T.; Gawalek, W.

    1999-01-01

    A simple approach to describe the levitation force measurements on melt-processed HTS bulks was developed. A couple of methods to determine the critical current density $J_c$ were introduced. The averaged $ab$-plane $J_c$ values for the field parallel to this plane were determined. The first and second levitation force hysteresis loops calculated with these $J_c$ values coincide remarkably well with the experimental data.

  6. Resistance of 4H-SiC Schottky barriers at high forward-current densities

    International Nuclear Information System (INIS)

    The resistance of Schottky barriers based on 4H-SiC is experimentally determined at high forward-current densities. The measured resistance is found to be significantly higher than the resistance predicted by classical mechanisms of electron transport in Schottky contacts. An assumption concerning the crucial contribution of the tunnel-transparent intermediate oxide layer between the metal and semiconductor to the barrier resistance is proposed and partially justified

  7. Measurements of current density distribution in shaped e-beam writers

    Czech Academy of Sciences Publication Activity Database

    Bok, Jan; Horáček, Miroslav; Kolařík, Vladimír; Urbánek, Michal; Matějka, Milan; Krzyžánek, Vladislav

    2016-01-01

    Roč. 149, JAN 5 (2016), s. 117-124. ISSN 0167-9317 R&D Projects: GA ČR(CZ) GA14-20012S; GA MŠk(CZ) LO1212; GA MŠk ED0017/01/01 Institutional support: RVO:68081731 Keywords : shaped e-beam writer * electron beam * current density Subject RIV: JB - Sensors, Measurment, Regulation Impact factor: 1.197, year: 2014

  8. What's All the Talc About? Air Entrainment in Dilute Pyroclastic Density Currents

    Science.gov (United States)

    Marshall, B. J.; Andrews, B. J.; Fauria, K.

    2015-12-01

    A quantitative understanding of air entrainment is critical to predicting the behaviors of dilute Pyroclastic Density Currents (PDCs), including runout distance, liftoff, and mass fractionation into co-PDC plumes. We performed experiments in an 8.5x6x2.6 meter tank using 20 micron talc powder over a range of conditions to describe air entrainment as a function of temperature, duration and mass flux. The experiments are reproducible and are scaled with respect to the densimetric and thermal Richardson numbers (Ri and RiT), Froude number, thermal to kinetic energy density ratio (TEb/KE), Stokes number, and Settling number, such that they are dynamically similar to natural dilute PDCs. Experiments are illuminated with a swept laser sheet and imaged at 1000 Hz to create 3D reconstructions of the currents, with ~1-2 cm resolution, at up to 1.5 Hz. An array of 30 high-frequency thermocouples record the precise temperature in the currents at 3 Hz. Bulk entrainment rates are calculated based on measured current volumes, surface areas, temperatures and velocities. Entrainment rates vary from ~0-0.9 and do not show simple variation with TEb/KE, Ri, or RiT. Entrainment does, however, increase with decreasing eruption duration and increasing mass flux. Our results suggest that current heads entrain air more efficiently than current bodies (>0.5 compared to ~0.1). Because shorter duration currents have proportionally larger heads, their bulk entrainment rates are controlled by those heads, whereas longer duration currents are dominated by their bodies. Our experiments demonstrate that air entrainment, which exerts a fundamental control on PDC runout and liftoff, varies spatially and temporally within PDCs.

  9. Specific features of an electric discharge operating between an electrolytic anode and a metal cathode

    Energy Technology Data Exchange (ETDEWEB)

    Gaisin, A. F.; Sarimov, L. R. [Kazan State Technical University (Russian Federation)

    2011-06-15

    Results are presented from experimental studies of a high-current electric discharge operating between an St45 steel cathode and a service water anode in a wide range of air pressures. Peculiarities of discharge ignition and specific features of cathode and anode spots were revealed. The behavior of the current density on a service water anode was investigated for the first time. Comparison of the current densities j on the steel cathode and service water anode shows that, in the parameter range under study, Hehl's law is not satisfied on the water anode. The two-dimensional distribution of the potential inside and on the surface of the service water anode was measured.

  10. Specific features of an electric discharge operating between an electrolytic anode and a metal cathode

    Science.gov (United States)

    Gaisin, A. F.; Sarimov, L. R.

    2011-06-01

    Results are presented from experimental studies of a high-current electric discharge operating between an St45 steel cathode and a service water anode in a wide range of air pressures. Peculiarities of discharge ignition and specific features of cathode and anode spots were revealed. The behavior of the current density on a service water anode was investigated for the first time. Comparison of the current densities j on the steel cathode and service water anode shows that, in the parameter range under study, Hehl's law is not satisfied on the water anode. The two-dimensional distribution of the potential inside and on the surface of the service water anode was measured.

  11. On the study of phase formation and critical current density in superconducting MgB2

    Indian Academy of Sciences (India)

    Suchitra Rajput; Sujeet Chaudhary; Subhash C Kashyap; Pankaj Srivastava

    2006-06-01

    Superconducting bulk MgB2 samples have been synthesized by employing sintering technique without using any additional process steps, generally undertaken in view of the substantial loss of magnesium, during heat treatment. Starting with Mg rich powders having different atomic ratios of Mg : B, as against the nominally required Mg : B = 1 : 2 ratio, we have obtained superconducting MgB2 samples of different characteristics. The effect of excess Mg in the starting mixture and processing temperature on the phase-formation, transition temperature (C) and critical current density (C) have been investigated by electrical transport and a.c. susceptibility measurements. The X-ray diffraction and X-ray photoelectron spectroscopic analyses of MgB2 bulk samples have been carried out to understand the role of excess Mg and the effect of processing temperature. It is established that MgB2 samples with high critical current density can be synthesized from a Mg rich powder having Mg : B in 2 : 2 ratio, at temperatures around 790°C. Critical current density has been found to vary systematically with processing temperature.

  12. Influence of current density on microstructure and properties of electrodeposited nickel-alumina composite coatings

    Energy Technology Data Exchange (ETDEWEB)

    Góral, Anna, E-mail: a.goral@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow (Poland); Nowak, Marek [Institute of Non-Ferrous Metals Gliwice, Light Metals Division Skawina, 19 Pilsudskiego St., 32-050 Skawina (Poland); Berent, Katarzyna; Kania, Bogusz [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow (Poland)

    2014-12-05

    Highlights: • Current density of the electrodeposition affects the incorporation of Al{sub 2}O{sub 3} in Ni matrix. • Ni/Al{sub 2}O{sub 3} composite coatings exhibit changes in crystallographic texture. • The pitting corrosion effects were observed in Ni/Al{sub 2}O{sub 3} coatings. • Residual stresses were decreased with increasing current density and coating thickness. - Abstract: Electrodeposition process is a very promising method for producing metal matrix composites reinforced with ceramic particles. In this method insoluble particles suspended in an electrolytic bath are embedded in a growing metal layer. This paper is focused on the investigations of the nickel matrix nanocomposite coatings with hard α-Al{sub 2}O{sub 3} nano-particles, electrochemically deposited from modified Watts-type baths on steel substrates. The influence of various current densities on the microstructure, residual stresses, texture, hardness and corrosion resistance of the deposited nickel/alumina coatings was investigated. The surface morphology, cross sections of the coatings and distribution of the ceramic particles in the metal matrix were examined by scanning electron microscopy. The phase composition, residual stresses and preferred grain orientation of the coatings were characterized using X-ray diffraction techniques. The coating morphology revealed that α-Al{sub 2}O{sub 3} particles show a distinct tendency to form agglomerates, approximately uniformly distributed into the nickel matrix.

  13. Influence of current density on microstructure and properties of electrodeposited nickel-alumina composite coatings

    International Nuclear Information System (INIS)

    Highlights: • Current density of the electrodeposition affects the incorporation of Al2O3 in Ni matrix. • Ni/Al2O3 composite coatings exhibit changes in crystallographic texture. • The pitting corrosion effects were observed in Ni/Al2O3 coatings. • Residual stresses were decreased with increasing current density and coating thickness. - Abstract: Electrodeposition process is a very promising method for producing metal matrix composites reinforced with ceramic particles. In this method insoluble particles suspended in an electrolytic bath are embedded in a growing metal layer. This paper is focused on the investigations of the nickel matrix nanocomposite coatings with hard α-Al2O3 nano-particles, electrochemically deposited from modified Watts-type baths on steel substrates. The influence of various current densities on the microstructure, residual stresses, texture, hardness and corrosion resistance of the deposited nickel/alumina coatings was investigated. The surface morphology, cross sections of the coatings and distribution of the ceramic particles in the metal matrix were examined by scanning electron microscopy. The phase composition, residual stresses and preferred grain orientation of the coatings were characterized using X-ray diffraction techniques. The coating morphology revealed that α-Al2O3 particles show a distinct tendency to form agglomerates, approximately uniformly distributed into the nickel matrix

  14. Development of large high current density superconducting solenoid magnets for use in high energy physics experiments

    International Nuclear Information System (INIS)

    The development of a unique type of large superconducting solenoid magnet, characterized by very high current density windings and a two-phase helium tubular cooling system is described. The development of the magnet's conceptual design and the construction of two test solenoids are described. The successful test of the superconducting coil and its tubular cooling refrigeration system is presented. The safety, environmental and economic impacts of the test program on future developments in high energy physics are shown. Large solid angle particle detectors for colliding beam physics will analyze both charged and neutral particles. In many cases, these detectors will require neutral particles, such as gamma rays, to pass through the magnet coil with minimum interaction. The magnet coils must be as thin as possible. The use of superconducting windings allows one to minimize radiation thickness, while at the same time maximizing charged particle momentum resolution and saving substantial quantities of electrical energy. The results of the experimental measurements show that large high current density solenoid magnets can be made to operate at high stored energies. The superconducting magnet development described has a positive safety and environmental impact. The use of large high current density thin superconducting solenoids has been proposed in two high energy physics experiments to be conducted at the Stanford Linear Accelerator Center and Cornell University as a result of the successful experiments described

  15. Exploring the sheet resistance variation with various beam current densities in low-energy ion implantation

    International Nuclear Information System (INIS)

    The effect of ion beam current density, varied from 0.2 to 0.5 mA/cm2, on electrical characteristics of the shallow junction is investigated. Given an implant energy at 10 keV and a constant phosphorus ion dose of 2.25 x 1015 cm-2, the sheet resistance of the implanted Si after rapid thermal annealing (RTA) increases (from 66 to 70 Ω/sq) with increasing beam current density. To investigate the sheet resistance variation, thermal wave, cross-sectional transmission electron microscopy and secondary ion mass spectrometry (SIMS) are conducted. These analyses identify that dose rate and dose shift are the factors relating to the sheet resistance variation. SIMS depth profiles of phosphorous, before and after RTA annealing, reveal that implantation with higher beam current density leads to a smaller integrated dose. It is also found that dose rate induced crystal damage has no effect on the sheet resistance variation. The cause of dose shift is explored and it should arise from the neutralized ion species which are not detected by the Faraday cup

  16. Influence of the anodic etching current density on the morphology of the porous SiC layer

    Directory of Open Access Journals (Sweden)

    Anh Tuan Cao

    2014-03-01

    Full Text Available In this report, we fabricated a porous layer in amorphous SiC thin films by using constant-current anodic etching in an electrolyte of aqueous diluted hydrofluoric acid. The morphology of the porous amorphous SiC layer changed as the anodic current density changed: At low current density, the porous layer had a low pore density and consisted of small pores that branched downward. At moderate current density, the pore size and depth increased, and the pores grew perpendicular to the surface, creating a columnar pore structure. At high current density, the porous structure remained perpendicular, the pore size increased, and the pore depth decreased. We explained the changes in pore size and depth at high current density by the growth of a silicon oxide layer during etching at the tips of the pores.

  17. The effect of current density and saccharin addition on the grain size of nickel coatings

    Energy Technology Data Exchange (ETDEWEB)

    Uhm, Young Rang; Park, Keun Yung; Son, Kwang Jae; Shim, Young Ho; Choi, Sun Ju [KAERI, Daejeon (Korea, Republic of)

    2012-10-15

    Recently, the main advantage of a radioisotope 'fuel' is concentrated, because it is 'burned' at the rate of the isotopes half life. In other words, given a half life of 100 years, a nuclear battery would still produce half of its initial starting power after 100 years. A speck of a radioisotope like nickel 63, for example, contains enough energy to power a nano nuclear battery for decades, and to do so safely. Ni 63, a beta radiation source, is prepared by electrical deposition of radioactive Ni 63 ions on thin non radioactive nickel foil. Ni 63 plating is similar to other electroplating processes that employ soluble metal anodes. It requires the passage of a direct current between two electrodes that are immersed in a conductive, aqueous solution of nickel salts. The charged Ni ions are formed by sulfate, sulfamate, chloride, and a Watts bath. However, the charged Ni 63 ions are formed by dissolving metal Ni 63. To establish the coating condition of Ni 63, non radioactive metal Ni particles were dissolved in an acid solution and electroplated on the Ni sheet. A continuous increase in the grain size versus current density has also been recognized in the direct current electrodeposition of nickel coating. On the other hand, A runa et al. reported that the current density has no significant effect on the grain size of nickel electro deposits. A review of the literature shows that saccharin has often been added to a nickel plating bath since the 1980s to improve the ductility and brightness, and in later periods as a grain refiner agent. In the present paper, not only the preparation of the Ni plating solution prepared by dissolving metal particles but also an optimization of the deposition conditions, such as the influence of current density and saccharin concentration on the grain size, was investigated. The proposed model can also be applied for radioactive Ni 63 electroplating.

  18. Analysis of a diode with a ferroelectric cathode

    International Nuclear Information System (INIS)

    It has been shown experimentally that electron current densities of more than 30 A/cm2 can be achieved from a cathode made of ferroelectric ceramic, when applying a field of order 0.1 MV/m. This current exceeds the Child--Langmuir current by two orders of magnitude. The current in the diode varies linearly with the applied voltage, provided that the latter is positive. In this theoretical study we show that the ferroelectric material plays a crucial role in the emission process. When a voltage is applied to the ferroelectric, the internal polarization field varies and the amount of screening charge required decreases. As a result, the electrons distribution near the cathode changes, forming a cloud which fills part of the diode gap. If now a positive voltage is applied to the anode, electrons are readily transferred through the diode gap. The qualitative and quantitative results of the theory are in good accordance with the experiment

  19. Synopsis of Cathode No.4 Activation

    International Nuclear Information System (INIS)

    The purpose of this report is to describe the activation of the fourth cathode installed in the DARHT-II Injector. Appendices have been used so that an extensive amount of data could be included without danger of obscuring important information contained in the body of the report. The cathode was a 612 M type cathode purchased from Spectra-Mat. Section II describes the handling and installation of the cathode. Section III is a narrative of the activation based on information located in the Control Room Log Book supplemented with time plots of pertinent operating parameters. Activation of the cathode was performed in accordance with the procedure listed in Appendix A. The following sections provide more details on the total pressure and constituent partial pressures in the vacuum vessel, cathode heater power/filament current, and cathode temperature

  20. Hybrid microwave oscillators with a virtual cathode

    International Nuclear Information System (INIS)

    A review is given of the developments and theoretical investigations of a fundamentally new class of microwave devices, namely, hybrid microwave oscillators with a virtual cathode, which combine the useful properties of virtual cathodes with the advantages of those traditional microwave oscillators that operate with subcritical-current beams and have a high efficiency in generating ultrarelativistic electron beams. Among such devices are the following: a hybrid diffractional microwave oscillator with a virtual cathode, a hybrid gyro-device with a virtual cathode, a hybrid beam-plasma vircator, a hybrid gyrocon with a virtual cathode, a hybrid Cherenkov oscillator with a virtual cathode, a hybrid microwave oscillator of the 'vircator + traveling-wave tube' type, an original two-beam tube with a virtual cathode, and a klystron-like vircator

  1. Analysis of nanosecond breaking of a high-density current in SOS diodes

    Science.gov (United States)

    Grekhov, I. V.; Lyublinskii, A. G.; Smirnova, I. A.

    2015-11-01

    Effect of a sharp (nanosecond) breaking of the reverse current with a density on the order of 103-104 A/cm2 in a silicon diode upon switching from direct to reverse bias voltage (so-called silicon opening switch, or SOS effect) is widely used in nanosecond technologies of gigawatt powers. For detailed analysis of the SOS effect, we constructed a special setup with small stray inductance, which makes it possible to test single SOS diodes with a working area of 1-2 mm2 in a wide range of current densities. Our experiments show, in particular, that the numerical model of the SOS effect developed at the Institute of Electrophysics, Ural Branch, Russian Academy of Sciences successfully described the experimental results. It is also shown that the charge extracted from the diode structure by the reverse current exceeds the charge introduced by a direct current pulse by not more than 10%, indicating a relatively small role of ionization processes. The possibility to carry out experiments on single samples with a small surface area allows us to study the SOS effect and considerably facilitates investigations aimed at the perfection of the design of SOS diodes.

  2. Large transport current density in bulk oriented-grained 123/Ag composites

    International Nuclear Information System (INIS)

    This paper reports on ceramic high temperature superconductors (HTS) that are inherently inferior in their mechanical properties. Addition of silver in bulk HTS has been shown to improve their mechanical properties. However, these HTS/Ag composites possess low transport critical current density typical of polycrystalline HTS. This paper deals with the development of a liquid-phase processing method that results in oriented-grained 123/Ag composites with large current carrying capability and enhanced mechanical properties. In this method, composites of 123 superconductor with up to 25 wt.% Ag addition are subjected to liquid-phase processing in air. Oriented-grained samples up to 10 mm long are obtained with Ag particles dispersed throughout the composites. Measurements on these oriented-grained samples using continuous direct current at 77K and zero applied magnetic field routinely give a transport critical current density in excess of 15,000 A/cm2. Magnetization measurements, however, show a Jc of 30,000 A/cm2 at 2 tesla. These results along with improved mechanical properties make these composites promising for bulk superconductivity applications. This work is supported by DARPA and the state of Texas

  3. Cancellation analysis of current density in solar active region NOAA10019

    Directory of Open Access Journals (Sweden)

    De Vita Gaetano

    2015-01-01

    Full Text Available Solar flares are often associated with changes in the fine magnetic structure of the emitting active region. Such topological modification results in variations of both the scaling properties of the fields’ fluctuations, and the fractal dimension of the associated gradients. The use of cancellation analysis of the current density has been attempted for the identification and quantitative estimation of such changes. The characteristics of the magnetic vector as measured by THEMIS telescope for the active region NOAA10019 have been studied in this paper, suggesting the presence of disrupted current filaments. The variation of the fractal dimension of the current structures, and in particular their smoothing, is discussed in relationship with occurrence of one flare in the active region.

  4. Durability and performance optimization of cathode materials for fuel cells

    Science.gov (United States)

    Colon-Mercado, Hector Rafael

    The primary objective of this dissertation is to develop an accelerated durability test (ADT) for the evaluation of cathode materials for fuel cells. The work has been divided in two main categories, namely high temperature fuel cells with emphasis on the Molten Carbonate Fuel Cell (MCFC) cathode current collector corrosion problems and low temperature fuel cells in particular Polymer Electrolyte Fuel Cell (PEMFC) cathode catalyst corrosion. The high operating temperature of MCFC has given it benefits over other fuel cells. These include higher efficiencies (>50%), faster electrode kinetics, etc. At 650°C, the theoretical open circuit voltage is established, providing low electrode overpotentials without requiring any noble metal catalysts and permitting high electrochemical efficiency. The waste heat is generated at sufficiently high temperatures to make it useful as a co-product. However, in order to commercialize the MCFC, a lifetime of 40,000 hours of operation must be achieved. The major limiting factor in the MCFC is the corrosion of cathode materials, which include cathode electrode and cathode current collector. In the first part of this dissertation the corrosion characteristics of bare, heat-treated and cobalt coated titanium alloys were studied using an ADT and compared with that of state of the art current collector material, SS 316. PEMFCs are the best choice for a wide range of portable, stationary and automotive applications because of their high power density and relatively low-temperature operation. However, a major impediment in the commercialization of the fuel cell technology is the cost involved due to the large amount of platinum electrocatalyst used in the cathode catalyst. In an effort to increase the power and decrease the cathode cost in polymer electrolyte fuel cell (PEMFC) systems, Pt-alloy catalysts were developed to increase its activity and stability. Extensive research has been conducted in the area of new alloy development and

  5. Studies in High Current Density Ion Sources for Heavy Ion Fusion Applications

    International Nuclear Information System (INIS)

    This dissertation develops diverse research on small (diameter ∼ few mm), high current density (J ∼ several tens of mA/cm2) heavy ion sources. The research has been developed in the context of a programmatic interest within the Heavy Ion Fusion (HIF) Program to explore alternative architectures in the beam injection systems that use the merging of small, bright beams. An ion gun was designed and built for these experiments. Results of average current density yield () at different operating conditions are presented for K+ and Cs+ contact ionization sources and potassium aluminum silicate sources. Maximum values for a K+ beam of ∼90 mA/cm2 were observed in 2.3 (micro)s pulses. Measurements of beam intensity profiles and emittances are included. Measurements of neutral particle desorption are presented at different operating conditions which lead to a better understanding of the underlying atomic diffusion processes that determine the lifetime of the emitter. Estimates of diffusion times consistent with measurements are presented, as well as estimates of maximum repetition rates achievable. Diverse studies performed on the composition and preparation of alkali aluminosilicate ion sources are also presented. In addition, this work includes preliminary work carried out exploring the viability of an argon plasma ion source and a bismuth metal vapor vacuum arc (MEVVA) ion source. For the former ion source, fast rise-times (∼ 1 (micro)s), high current densities (∼ 100 mA/cm2) and low operating pressures (epsilon)n (le) 0.006 π mm · mrad) although measured currents differed from the desired ones (I ∼ 5mA) by about a factor of 10

  6. Studies in High Current Density Ion Sources for Heavy Ion FusionApplications

    Energy Technology Data Exchange (ETDEWEB)

    Chacon-Golcher, E.

    2002-06-01

    This dissertation develops diverse research on small (diameter {approx} few mm), high current density (J {approx} several tens of mA/cm{sup 2}) heavy ion sources. The research has been developed in the context of a programmatic interest within the Heavy Ion Fusion (HIF) Program to explore alternative architectures in the beam injection systems that use the merging of small, bright beams. An ion gun was designed and built for these experiments. Results of average current density yield () at different operating conditions are presented for K{sup +} and Cs{sup +} contact ionization sources and potassium aluminum silicate sources. Maximum values for a K{sup +} beam of {approx}90 mA/cm{sup 2} were observed in 2.3 {micro}s pulses. Measurements of beam intensity profiles and emittances are included. Measurements of neutral particle desorption are presented at different operating conditions which lead to a better understanding of the underlying atomic diffusion processes that determine the lifetime of the emitter. Estimates of diffusion times consistent with measurements are presented, as well as estimates of maximum repetition rates achievable. Diverse studies performed on the composition and preparation of alkali aluminosilicate ion sources are also presented. In addition, this work includes preliminary work carried out exploring the viability of an argon plasma ion source and a bismuth metal vapor vacuum arc (MEVVA) ion source. For the former ion source, fast rise-times ({approx} 1 {micro}s), high current densities ({approx} 100 mA/cm{sup 2}) and low operating pressures (< 2 mtorr) were verified. For the latter, high but acceptable levels of beam emittance were measured ({var_epsilon}{sub n} {le} 0.006 {pi} mm {center_dot} mrad) although measured currents differed from the desired ones (I {approx} 5mA) by about a factor of 10.

  7. Current Density-Functional Theory using meta-Generalized Gradient Exchange--Correlation Functionals

    CERN Document Server

    Furness, James W; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

    2015-01-01

    We present the self-consistent implementation of current-dependent (hybrid) meta generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn--Sham current density-functional theory (KS-CDFT). A unique feature of the non-perturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 a.u. ($\\sim 235000$T) in strength. CDFT functionals based on the TPSS and B98 forms are investigated and their performance is assessed by comparison with accurate CCSD(T) data. In the weak field regime magnetic properties such as magnetizabilities and NMR shielding constants show modest but systematic improvements over GGA functionals. However, in strong field regime the mGGA based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T...

  8. Micro-hollow cathode dischargers

    International Nuclear Information System (INIS)

    In order to develop a hollow cathode discharge (HCD) with its increased current over planar electrode glow discharges, the cathode fall, which is on the order of the mean free path for ionization, must be comparable in length to the hole diameter. This indicates that the discharge parameters vary with pressure, p, times hole diameter, D. The pD product for stable operation of a hollow cathosde discharge was quoted to be on the order of one to ten Torr cm for noble gases, less for molecular gases. White (1959) observed the hollow cathode effect in a neon discharge at a pressure of 100 Torr when the hole dimensions were less than 1 mm. The cathode hole in his experiments changed from a cylindrical into a spherical cavity due to sputtering. The anode consisted in White's experiment of a pin on the axis of the discharge geometry. We have studied micro-hollow (submillimeter) cathode discharges between two electrodes with aligned cylindrical holes by determining the current-voltage characteristics and the visual appearance of the discharge in argon over a wide range of pressure and voltage. The cross-section of the discharge geometry. The cathode is made of molybdenum or barium oxide inserted into a tungsten matrix (dispenser-cathode), the anode of molybdenum, and the dielectric spacer is mica. The discharge was operated under dc conditions, with half-wave rectified ac voltage applied, and pulsed with a 400 μs rectangular voltage pulse. The lower limit in pressure was determined by the maximum voltage which could be applied to the discharge geometry without breakdown along insulators. The upper limit, in this study, is determined by the transition from cathode electrode emission due to ion-impact to thermal emission of electrons, which causes a dramatic increase in current and a drop in forward voltage to values on the order of 20 V

  9. A multiple gap plasma cathode electron gun and its electron beam analysis in self and trigger breakdown modes

    Science.gov (United States)

    Kumar, Niraj; Pal, Dharmendra Kumar; Jadon, Arvind Singh; Pal, Udit Narayan; Rahaman, Hasibur; Prakash, Ram

    2016-03-01

    In the present paper, a pseudospark discharge based multiple gap plasma cathode electron gun is reported which has been operated separately in self and trigger breakdown modes using two different gases, namely, argon and hydrogen. The beam current and beam energy have been analyzed using a concentric ring diagnostic arrangement. Two distinct electron beams are clearly seen with hollow cathode and conductive phases. The hollow cathode phase has been observed for ˜50 ns where the obtained electron beam is having low beam current density and high energy. While in conductive phase it is high current density and low energy electron beam. It is inferred that in the hollow cathode phase the beam energy is more for the self breakdown case whereas the current density is more for the trigger breakdown case. The tailor made operation of the hollow cathode phase electron beam can play an important role in microwave generation. Up to 30% variation in the electron beam energy has been achieved keeping the same gas and by varying the breakdown mode operations. Also, up to 32% variation in the beam current density has been achieved for the trigger breakdown mode at optimized trigger position by varying the gas type.

  10. Effects of the current boundary conditions at the plasma-gun gap on density in SSPX

    Science.gov (United States)

    Kolesnikov, Roman; Lodestro, L. L.; Meyer, W. H.

    2012-10-01

    The Sustained Spheromak Physics Experiment (SSPX) was a toroidal magnetic-confinement device without toroidal magnetic-field coils or a central transformer but which generated core-plasma currents by dynamo processes driven by coaxial plasma-gun injection into a flux-conserving vessel. Record electron temperatures in a spheromak (Te˜500eV) were achieved, and final results of the SSPX program were reported in [1]. Plasma density, which depended strongly on wall conditions, was an important parameter in SSPX. It was observed that density rises with Igun and that confinement improved as the density was lowered. Shortly after the last experiments, a new feature was added to the Corsica code's solver used to reconstruct SSPX equilibria. Motivated by n=0 fields observed in NIMROD simulations of SSPX, an insulating boundary condition was implemented at the plasma-gun gap. Using this option we will perform new reconstructions of SSPX equilibria and look for correlations between the location of the separatrix (which moves up the gun wall and onto the insulating gap as Igun increases) and plasma density and magnetic-flux amplification [2].[4pt] [1] H. S. McLean, APS, DPP, Dallas, TX, 2008.[0pt] [2] E. B. Hooper et al., Nucl. Fusion 47, 1064 (2007).

  11. Hollow cathode lamp-construction aspects

    International Nuclear Information System (INIS)

    The hollow cathode discharge is a source used for absorption and fluorescence atomic spectrophotometry. In this paper various aspect like construction, cleanliness and operation have been described. The life time of the hollow cathode discharge for specific current is about 500 hs. The range of current for the non significant self-absorption of the recommended wavelenght has been determinated. (Author)

  12. Water Dissociation Phenomena on a Bipolar Membrane——Current-voltage Curve in Relation with Ionic Transport and Limiting Current Density

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer exists at the junction of a bipolar membrane, which is coincided with the viewpoint of the most literatures, but we also consider that the thickness and conductivity of this layer is not only related with the increase of the applied voltage but also with the limiting current density. Below the limiting current density, the thickness of the depletion layer keeps a constant and the conductivity decreases with the increase of the applied voltage;while above the limiting current density, the depletion thickness will increase with the increase of the applied voltage and the conductivity keeps a very low constant. Based on the data reported in the literatures and independent determinations, the limiting current density was calculated and the experimental curves Ⅰ- Ⅴ in the two directions were compared with the theoretical calculations. It is demonstrated that above the limiting current density, the experimental results,either in the L-H direction or in the H-L direction, are consistent with the theoretical calculations; below the limiting current density, a slight deviation exists between the experimental and the theoretical results, and between the experimental results in the two directions. The change in Donnan potential due to the asymmetry of the mono-layers and the changes of ionic composition in the two directions is possibly responsible for this deviation.

  13. Radiation effects on critical current density in Ba2YCu3O7 superconductor

    International Nuclear Information System (INIS)

    This paper summarizes some experimental data on electron and ion irradiation effects on the superconducting properties of Ba2YCu3O7-x pellets. Discussion is made in relation to radiation-induced critical current enhancement and results of in-situ microstructural observations during electron irradiation in a transmission electron microscope. Observations indicate that the critical current density of the pellet is enhanced by electron irradiation. When the Ba2YCu3O7 pellets are irradiated with 200 keV O- or N-ions at ambient temperature, the superconducting transition temperature measured with current density greater than 15 kA·m-2 is increased by the ion-irradiation to a fluence of about 1 x 1015m-2. Changes in the superconducting properties of the Ba2YCu3O7 pellet with MeV-electron and ion irradiation can be understood in relation to microstructural changes induced by electron irradiation in a transmission electron microscope. (N.K.)

  14. Anomalous plasma heating induced by modulation of the current-density profile

    International Nuclear Information System (INIS)

    The usual plasma heating in a tokamak needs additional heating to reach ignition temperature (approx. 108 K). The method used in the TORTUR III experiment is to induce anomalous plasma resistivity by applying a short (10 microseconds) high-voltage pulse. A sharp rise of the plasma temperature is found almost simultaneously, but this effect, though considerable, is too short-lived to be of interest for a thermonuclear chain reaction. A second pulse gives a second rise of temperature, but this time a slow one, extending over several milliseconds. The mechanism of this delayed heating and the reservoir within the plasma supplying the energy are subjects of investigation in the TORTUR III experiments. Some conclusions concerning the plasma heating mechanism are presented. The conclusion is reached that the application of the high-voltage pulse results in a modulation of the current-density profile: the (normally already peaked) profile sharpens, the current concentrates in the centre of the plasma column. This is a non-equilibrium situation. It relaxes to the noraml current distribution within approximately 2 milliseconds. As long as this relaxation process is not finished, the dissipation is on an enhanced level and anomalous plasma heating is observed. Many plasma parameters are surveyed and evaluated: temperature (both of the ions and the electrons), density, emission spectrum (from microwaves to hard X-rays) and the fluctuation spectrum. Main subject of this report is the measurement and interpretation of the X-rays of the emission spectrum. Experimental results are presented and discussed

  15. Observation of radio frequency ring-shaped hollow cathode discharge plasma with MgO and Al electrodes for plasma processing

    International Nuclear Information System (INIS)

    Various high-density plasma sources have been proposed for plasma processing. Especially, the hollow cathode discharge is one of the powerful ones. In this work, radio-frequency (RF) driven ring-shaped hollow cathode discharges with high secondary-electron emission have been investigated, using an aluminum (Al) cathode, coated or not with magnesium oxide (MgO). The thickness of MgO thin film is approximately 200 nm. The RF discharge voltage for the coated cathode is almost the same as that for the uncoated one, in a wide range of Ar gas pressure, from 5.3 to 53.2 Pa. The results reveal that the plasma density has a peak at an Ar gas pressure of 10.6 Pa for both cathodes. The plasma density for the coated cathode is about 1.5–3 times higher than that for the uncoated one, at various gas pressures. To the contrary, the electron temperature for the coated cathode is lower than temperature obtained with the uncoated cathode, at various gas pressures. Radial profiles of electron saturation current, which is proportional to plasma flux, are also examined for a wide range of gas pressure. Radial profiles of electron temperature at various axial positions are almost uniform for both cathodes so that the diffusion process due to density gradient is dominant for plasma transport. The secondary electrons emitted from the coated cathode contribute to the improvement of the plasma flux radial profile obtained using the uncoated cathode

  16. Density effect on critical current density and flux pinning properties of polycrystalline SmFeAsO1 - xFx superconductor

    Science.gov (United States)

    Ding, Y.; Sun, Y.; Zhuang, J. C.; Cui, L. J.; Shi, Z. X.; Sumption, M. D.; Majoros, M.; Susner, M. A.; Kovacs, C. J.; Li, G. Z.; Collings, E. W.; Ren, Z. A.

    2011-12-01

    A series of polycrystalline SmFeAs1 - xOx bulks was prepared to systematically investigate the influence of sample density on flux pinning properties. Different sample densities were achieved by controlling the pelletizing pressure. The superconducting volume fraction, the critical current densities Jcm and the flux pinning force densities Fp were estimated from the magnetization measurements. Experimental results show that: (1) the superconducting volume fraction increases with the increasing of sample density; (2) the Jcm values have a similar trend except for the sample with very high density due to different connectivity and pinning mechanisms, moreover, the Jcm(B) curve develops a peak effect at approximately the same field at which the high density sample shows a kink; (3) the Fp(B) curve of the high density sample shows a low-field peak and a high-field peak at several temperatures, which can be explained by improved intergranular current, while only one peak can be observed in Fp(B) of the low density samples. Based on the scaling behaviour of flux pinning force densities, the main intragranular pinning is normal point pinning.

  17. Density effect on critical current density and flux pinning properties of polycrystalline SmFeAsO1−xFx superconductor

    International Nuclear Information System (INIS)

    A series of polycrystalline SmFeAs1−xOx bulks was prepared to systematically investigate the influence of sample density on flux pinning properties. Different sample densities were achieved by controlling the pelletizing pressure. The superconducting volume fraction, the critical current densities Jcm and the flux pinning force densities Fp were estimated from the magnetization measurements. Experimental results show that: (1) the superconducting volume fraction increases with the increasing of sample density; (2) the Jcm values have a similar trend except for the sample with very high density due to different connectivity and pinning mechanisms, moreover, the Jcm(B) curve develops a peak effect at approximately the same field at which the high density sample shows a kink; (3) the Fp(B) curve of the high density sample shows a low-field peak and a high-field peak at several temperatures, which can be explained by improved intergranular current, while only one peak can be observed in Fp(B) of the low density samples. Based on the scaling behaviour of flux pinning force densities, the main intragranular pinning is normal point pinning.

  18. Effect of the proximity of the Heliospheric Current Sheet on the heliospheric magnetic flux density

    Science.gov (United States)

    Erdös, Géza; Balogh, André

    2014-05-01

    In recent work (Erdős & Balogh, ApJ., 781, 50, 2014) it has been shown that the magnetic flux density measured by the Ulysses probe around its solar polar orbit from 1990 to 2009 matches that calculated from the OMNI in-ecliptic, 1 AU data set over the same interval. This result has shown that the sun's magnetic flux is generally distributed uniformly in the heliosphere and depends only on the total open magnetic flux of the sun. We have nevertheless examined those two intervals in the nearly 20-year long observations, when the flux density measured at Ulysses appears to be greater than that observed at 1 AU. The two intervals are near the minima in solar activity in 1995-96 and 2007-08, with the difference in the first interval noticeably larger than in the second. We show that the difference between the Ulysses and the OMNI results are strongly correlated to the distance between the Heliospheric Current Sheet (HCC) and the 1 AU observation point, with the flux density smaller at the in ecliptic observation point than at Ulysses which during those intervals was generally well north or south of the HCC. A corresponding result can also be identified as a longitude dependence in the magnetic flux density when comparing the observations by the STEREO-A and -B spacecraft which are close to 1 AU in the ecliptic, but are widely separated in heliolongitude. We discuss possible causes of the reduced flux density near the HCC in terms of the geometric effects on the uniform spreading of the solar magnetic flux and the possible effect of magnetic reconnection associated with the HCC and the properties of the slow wind in which it is embedded.

  19. Real-time control of the current density profile in JET

    International Nuclear Information System (INIS)

    In this paper we describe experiments illustrating a multi-variable model-based technique whose purpose is to control the current and pressure profiles in tokamak with internal transport barriers. This method uses a truncated singular value decomposition of a linearized model operator and offers the potentiality of retaining the distributed character of the current and heat diffusion. We begin with the simplest, lumped-parameter version of this technique, it is shown that with only one actuator, a satisfactory control of the safety factor profile (q-profile) can be achieved within the accessible one-parameter family of profiles, i.e with a steady state offset between the requested profile and the achieved one which is minimum in the least square sense. The first experiments using a multiple-input and multiple-output (MIMO) controller to control the q-profile with 3 heating and current drive actuators, namely neutral beam injection, ion cyclotron resonant heating and lower hybrid current drive, are reported. In the last part we present a simulation of the simultaneous control of plasma current density and pressure profile by using a state space method to obtain a linear mode of plasma dynamics

  20. Real-time control of the current density profile in JET

    Energy Technology Data Exchange (ETDEWEB)

    Moreau, D. [Efda-Jet-Csu, Culham Fusion Centre, Abingdon, OX (United Kingdom); Moreau, D.; Litaudon, X.; Mazon, D.; Joffrin, E.; Laborde, L.; Lennholm, M.; Tresset, G.; Zabeo, L. [Association Euratom-CEA Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Crisanti, F.; Albanese, R.; Ariola, M.; Pironti, A.; Pericolf-Ridolfini, V.; Riva, M. [Association Euratom-ENEA sulla Fusione Centro Ricerche Energia Frascati (Italy); Vries, P. de [Association Euratom-Fom, TEC Cluster, Neuwegein (Netherlands); Felton, R.; Zastrow, K.D. [Association Euratom-Ukaea, Culham Science Centre, Abingdon (United Kingdom); Murari, A. [Association Euratom-ENEA, Consorzio RFX, Padova (Italy); Tala, T. [Association Euratom-Tekes, Helsinki University of Technology (Finland)

    2004-07-01

    In this paper we describe experiments illustrating a multi-variable model-based technique whose purpose is to control the current and pressure profiles in tokamak with internal transport barriers. This method uses a truncated singular value decomposition of a linearized model operator and offers the potentiality of retaining the distributed character of the current and heat diffusion. We begin with the simplest, lumped-parameter version of this technique, it is shown that with only one actuator, a satisfactory control of the safety factor profile (q-profile) can be achieved within the accessible one-parameter family of profiles, i.e with a steady state offset between the requested profile and the achieved one which is minimum in the least square sense. The first experiments using a multiple-input and multiple-output (MIMO) controller to control the q-profile with 3 heating and current drive actuators, namely neutral beam injection, ion cyclotron resonant heating and lower hybrid current drive, are reported. In the last part we present a simulation of the simultaneous control of plasma current density and pressure profile by using a state space method to obtain a linear mode of plasma dynamics.

  1. Internally Oxidized Nb3Sn Strands with Fine Grain Size and High Critical Current Density

    OpenAIRE

    Xu, Xingchen; Sumption, Michael D.; Peng, Xuan

    2014-01-01

    Nb3Sn superconducting strands are the most practical conductors to generate high magnetic fields (12-16 T), and thus have significant applications in nuclear magnetic resonance (NMR), and great potential for fusion reactors and particle accelerator magnets. High critical current density (Jc) is a key parameter for such applications. Significant efforts towards optimization of various factors led to an 80% improvement in Jc from the early 1990s to 2003, when the 4.2 K, 12 T non-matrix Jc reach...

  2. High current density electropolishing in the preparation of highly smooth substrate tapes for coated conductors

    Energy Technology Data Exchange (ETDEWEB)

    Kreiskott, Sascha (Los Alamos, NM); Matias, Vladimir (Santa Fe, NM); Arendt, Paul N. (Los Alamos, NM); Foltyn, Stephen R. (Los Alamos, NM); Bronisz, Lawrence E. (Los Alamos, NM)

    2009-03-31

    A continuous process of forming a highly smooth surface on a metallic tape by passing a metallic tape having an initial roughness through an acid bath contained within a polishing section of an electropolishing unit over a pre-selected period of time, and, passing a mean surface current density of at least 0.18 amperes per square centimeter through the metallic tape during the period of time the metallic tape is in the acid bath whereby the roughness of the metallic tape is reduced. Such a highly smooth metallic tape can serve as a base substrate in subsequent formation of a superconductive coated conductor.

  3. Temperature-dependence of Threshold Current Density-Length Product in Metallization Lines: A Revisit

    Science.gov (United States)

    Saptono Duryat, Rahmat; Kim, Choong-Un

    2016-04-01

    One of the important phenomena in Electromigration (EM) is Blech Effect. The existence of Threshold Current Density-Length Product or EM Threshold has such fundamental and technological consequences in the design, manufacture, and testing of electronics. Temperature-dependence of Blech Product had been thermodynamically established and the real behavior of such interconnect materials have been extensively studied. The present paper reviewed the temperature-dependence of EM threshold in metallization lines of different materials and structure as found in relevant published articles. It is expected that the reader can see a big picture from the compiled data, which might be overlooked when it was examined in pieces.

  4. Effect of Current Density on Thermal and Optical Properties of p-Type Porous Silicon

    International Nuclear Information System (INIS)

    The different parameters of the porous silicon (PSi) can be tuned by changing some parameters in preparation process. We have chosen the anodization as formation method, so the related parameters should be changed. In this study the porous silicon (PSi) layers were formed on p-type Si wafer. The samples were anodized electrically in a fixed etching time under some different current densities. The structural and optical properties of porous silicon (PSi) on silicon (Si) substrates were investigated using photoluminescence (PL) and Photoacoustic Spectroscopy (PAS). (author)

  5. System and method for magnetic current density imaging at ultra low magnetic fields

    Science.gov (United States)

    Espy, Michelle A.; George, John Stevens; Kraus, Robert Henry; Magnelind, Per; Matlashov, Andrei Nikolaevich; Tucker, Don; Turovets, Sergei; Volegov, Petr Lvovich

    2016-02-09

    Preferred systems can include an electrical impedance tomography apparatus electrically connectable to an object; an ultra low field magnetic resonance imaging apparatus including a plurality of field directions and disposable about the object; a controller connected to the ultra low field magnetic resonance imaging apparatus and configured to implement a sequencing of one or more ultra low magnetic fields substantially along one or more of the plurality of field directions; and a display connected to the controller, and wherein the controller is further configured to reconstruct a displayable image of an electrical current density in the object. Preferred methods, apparatuses, and computer program products are also disclosed.

  6. Perpendicular ac susceptibility and critical current density of distant superconducting twin films

    International Nuclear Information System (INIS)

    The complex ac susceptibility χ' - jχ'' of a pair of distant square superconducting twin films is calculated based on the critical-state model with a constant critical current density Jc. The results are compared with the measured ones of several pairs of square superconducting films. The theoretical and experimental results agree qualitatively with interesting quantitative differences. It is found that the product of the low-field χ' and the field amplitude Hm at maximum χ'' is insensitive to the film distance, so that the formula for Jc determination of a single film from ac susceptibility measurements may be used for twin films.

  7. Structural, optical and electrical characterization of nanostructured porous silicon: Effect of current density.

    Science.gov (United States)

    Kulathuraan, K; Mohanraj, K; Natarajan, B

    2016-01-01

    In this work, an attempt has been made to fabricate porous silicon (PS) from p-type crystalline silicon (c-Si) wafers by using the electrochemical etching process at six different current densities (40, 60, 75, 100, 125 and 150mA/cm(2)) with constant time (30min). The influence of varying current density on morphological, structural, optical and electrical properties of PS samples were analyzed by using SEM, AFM, XRD, FT-IR, PL and electrical (I-V) techniques, respectively. Microstructural images clearly showed that the average pore diameter and thickness increase with increase current densities up to 100mA/cm(2) and decrease for 125mA/cm(2). It could be related to breaking of pore walls and exposing to the next layer of c-Si. Further increase the current density about 150mA/cm(2), the average pore diameter increase as in the case of first layer (40-100mA/cm(2)) of c-Si wafer. The result is reflected in PL emission band (at 708nm) and the intensity of the emission band shifted towards red region. The X-ray diffraction pattern confirm the formation of porous silicon as appeared as a broad peak at 2θ=69.3° belongs to (400) reflection. The FTIR study supports the X-ray diffraction analysis that shows the vibrational bands of S-H2 and Si-O-Si at 2109cm(-1), 915cm(-1) and 615cm(-1) and 1107cm(-1), respectively. The I-V characteristic of PS exhibited rectifying behavior with different values of ideality factor (η) and barrier height (ϕb). It is concluded from the experimental results that the formed pores developed up to 100mA/cm(2) in the top layer of c-Si and the formed pores exposed to the next layer of c-Si when increase the high electrochemical etching process (above 100mA/cm(2)). PMID:26186397

  8. Intra- and inter-grain critical current density in (Cu,C):1234 superconductors

    International Nuclear Information System (INIS)

    From DC magnetization studies in fields up to 14 T and temperatures between 20 and 100 K, we estimated the intra- and inter-grain critical current density Jc of (Cu,C):1234 high-Tc superconductors, in the frame of critical state models. The inter-grain Jc was determined by comparing the magnetization loops of as-grown sample and of the ground sample. Finally, short comments on Jc resulted from AC susceptibility measurements and of the impressive increase of intra-grain Jc due to heavy-ion and neutron irradiation are presented

  9. Preparation of nanocomposite thoriated tungsten cathode by swaging technique

    Institute of Scientific and Technical Information of China (English)

    王发展; 诸葛飞; 张晖; 丁秉钧

    2002-01-01

    By using the high energy ball milling method,the nanosized ThO2 powders were obtained.Through mixing powders,sintering and hot swaging processing,a nanocomposite thoriated tungsten cathode was fabricated.The relative density of the nanocomposite material is near 100%.The microstructure of nanocomposite cathode is quite different from that of conventional thoriated tungsten cathode.Most of thoria particles are less than 100 nm in diameter,and distribute on the boundaries of tungsten grains.The nanocomposite cathode shows a much lower arc starting field than that of conventional cathode,which will improve the performance of the cathode significantly.

  10. A new insight into the oxygen diffusion in porous cathodes of lithium-air batteries

    International Nuclear Information System (INIS)

    Slow air transport in the cathodes limits the performance of the metal-air battery. In this work, the diffusion mechanisms in the lithium-air battery have been investigated. It has been found that Knudsen diffusivity can be influenced dramatically by the different pore sizes while bulk diffusivity is almost a constant at a fixed temperature. Limiting current density and concentration polarization, both limited by impeded gas diffusion in the porous cathode, have been evaluated systematically. The analysis of the correlation between those electrochemical parameters and diffusivities improves the quantitative evaluation of gas-based batteries at various materials and operation conditions. - Highlights: • Gas diffusion models are applied to evaluate the lithium-air battery cathode. • Knudsen and bulk diffusivities are introduced to analyze cathode materials. • Analysis is performed for assessing the battery efficiency

  11. Composite Cathodes for Dual-Rate Li-Ion Batteries

    Science.gov (United States)

    Whitacre, Jay; West, William; Bugga, Ratnakumar

    2008-01-01

    Composite-material cathodes that enable Li-ion electrochemical cells and batteries to function at both high energy densities and high discharge rates are undergoing development. Until now, using commercially available cathode materials, it has been possible to construct cells that have either capability for high-rate discharge or capability to store energy at average or high density, but not both capabilities. However, both capabilities are needed in robotic, standby-power, and other applications that involve duty cycles that include long-duration, low-power portions and short-duration, high-power portions. The electrochemically active ingredients of the present developmental composite cathode materials are: carbon-coated LiFePO4, which has a specific charge capacity of about 160 mA h/g and has been used as a high-discharge-rate cathode material and Li[Li(0.17)Mn(0.58)Ni(0.25)]O2, which has a specific charge capacity of about 240 mA h/g and has been used as a high-energy-density cathode material. In preparation for fabricating the composite material cathode described, these electrochemically active ingredients are incorporated into two sub-composites: a mixture comprising 10 weight percent of poly(vinylidine fluoride); 10 weight percent of carbon and 80 weight percent of carbon coated LiFePO4; and, a mixture comprising 10 weight percent of PVDF, and 80 weight percent of Li[Li(0.17)Mn(0.58)Ni(0.25)]O2. In the fabrication process, these mixtures are spray-deposited onto an aluminum current collector. Electrochemical tests performed thus far have shown that better charge/discharge performance is obtained when either 1) each mixture is sprayed on a separate area of the current collector or (2) the mixtures are deposited sequentially (in contradistinction to simultaneously) on the same current-collector area so that the resulting composite cathode material consists of two different sub-composite layers.

  12. Density-matrix renormalization-group study of current and activity fluctuations near nonequilibrium phase transitions.

    Science.gov (United States)

    Gorissen, Mieke; Hooyberghs, Jef; Vanderzande, Carlo

    2009-02-01

    Cumulants of a fluctuating current can be obtained from a free-energy-like generating function, which for Markov processes equals the largest eigenvalue of a generalized generator. We determine this eigenvalue with the density-matrix renormalization group for stochastic systems. We calculate the variance of the current in the different phases, and at the phase transitions, of the totally asymmetric exclusion process. Our results can be described in the terms of a scaling ansatz that involves the dynamical exponent z . We also calculate the generating function of the dynamical activity (total number of configuration changes) near the absorbing-state transition of the contact process. Its scaling properties can be expressed in terms of known critical exponents. PMID:19391693

  13. Unified models of E-layer plasma turbulence from density gradients and Hall currents

    Science.gov (United States)

    Hassan, Ehab; Litt, Sandeep; Horton, Wendell; Smolyakov, Andrei; Skiff, Fred

    2013-10-01

    The Earth's ionosphere is rich with plasma irregularities of scale-lengths extend from few centimeters to hundreds of kilometers. The combination of small-scale turbulence with large coherent structures is at the forefront of basic plasma turbulence theory. A new unified model for the small-scale plasma turbulence called Type-I and Type-II in the E-region ionosphere is presented. Simulations and a proposed laboratory experiment for these plasma waves in a weakly ionized plasma are reported. The ions [Argon in the lab and NO+ in the ionosphere] are collisional and the electrons ExB drifts produce Hall currents. The dispersion relations are analyzed for both density gradient and electron current driven instabilities. A basic understanding of the turbulence is important for forecasting disruptions in GNSS communication signals from RF signal scattering produced by the E-layer plasma turbulence on the 10cm to 10m scales lengths. NSF:AGS-0964692.

  14. Critical current density of MgB2 thin films and the effect of interface pinning

    International Nuclear Information System (INIS)

    Preferentially oriented MgB2 thin films with c-axis normal to the surface have been prepared and characterized for microstructure and transport properties. The magnetic field dependence of superconducting critical current density Jc has been determined from the magnetization hysteresis (M-H) loops at various temperatures using the Bean's critical state model. High Jc of these films show their potential for applications. We have also measured the angular dependences of Jc. The angular dependence is seen to be in agreement with the anisotropic Ginzburg-Landau model except that at angles close to the ab plane, increased pinning due to film-substrate interaction is observed. The angular range where interface pinning is effective has been determined by measurement of asymmetry in dissipation on reversal of current for fields applied at angles close to the ab plane

  15. First test of BNL electron beam ion source with high current density electron beam

    Science.gov (United States)

    Pikin, Alexander; Alessi, James G.; Beebe, Edward N.; Shornikov, Andrey; Mertzig, Robert; Wenander, Fredrik; Scrivens, Richard

    2015-01-01

    A new electron gun with electrostatic compression has been installed at the Electron Beam Ion Source (EBIS) Test Stand at BNL. This is a collaborative effort by BNL and CERN teams with a common goal to study an EBIS with electron beam current up to 10 A, current density up to 10,000 A/cm2 and energy more than 50 keV. Intensive and pure beams of heavy highly charged ions with mass-to-charge ratio heavy ion research facilities including NASA Space Radiation Laboratory (NSRL) at BNL and HIE-ISOLDE at CERN. With a multiampere electron gun, the EBIS should be capable of delivering highly charged ions for both RHIC facility applications at BNL and for ISOLDE experiments at CERN. Details of the electron gun simulations and design, and the Test EBIS electrostatic and magnetostatic structures with the new electron gun are presented. The experimental results of the electron beam transmission are given.

  16. Hydrogen production in single chamber microbial electrolysis cells with stainless steel fiber felt cathodes

    Science.gov (United States)

    Su, Min; Wei, Liling; Qiu, Zhaozheng; Wang, Gang; Shen, Jianquan

    2016-01-01

    Microbial electrolysis cell (MEC) is a promising technology for sustainable production of hydrogen from biodegradable carbon sources. Employing a low-cost and high efficient cathode to replace platinum catalyzed cathode (Pt/C) for hydrogen generation is a challenge for commercialization of MEC. Here we show that a 3D macroporous stainless steel fiber felt (SSFF) with high electrochemical active surface area has an excellent catalytic activity for hydrogen generation, which is comparable to Pt/C cathode and superior to stainless steel mesh (SSM) cathode in the single-chamber MEC. The SSFF cathode (mean filter rating 100 μm) produces hydrogen at a rate of 3.66 ± 0.43 m3 H2 m-3d-1 (current density of 17.29 ± 1.68 A m-2), with a hydrogen recovery of 76.37 ± 15.04% and overall energy efficiency of 79.61 ± 13.07% at an applied voltage of 0.9 V. The performance of SSFF cathode improves over time due to a decrease in overpotential which caused by corrosion. These results demonstrate that SSFF can be a promising alternative for Pt catalytic cathode in MEC for hydrogen production.

  17. Anomalous isotopic distribution of elements deposited on palladium induced by cathodic electrolysis

    International Nuclear Information System (INIS)

    It was confirmed by several analytic methods that reaction products with atomic number ranging from 20 to 28, 46 to 54, and 72 to 82 are detected in palladium cathodes subjected to electrolysis in a heavy water solution at high pressure, high temperature and by high current density for one month. Isotopic distributions were radically different from the natural ones. (author)

  18. Growth and characterization of high current density, high-speed InAs/AlSb resonant tunneling diodes

    Science.gov (United States)

    Soderstrom, J. R.; Brown, E. R.; Parker, C. D.; Mahoney, L. J.; Yao, J. Y.

    1991-01-01

    InAs/AlSb double-barrier resonant tunneling diodes with peak current densities up to 370,000 A/sq cm and high peak-to-valley current ratios of 3.2 at room temperature have been fabricated. The peak current density is well-explained by a stationary-state transport model with the two-band envelope function approximation. The valley current density predicted by this model is less than the experimental value by a factor that is typical of the discrepancy found in other double-barrier structures. It is concluded that threading dislocations are largely inactive in the resonant tunneling process.

  19. Truncation planes from a dilute pyroclastic density current: field data and analogue experiments.

    Science.gov (United States)

    Douillet, Guilhem Amin; Gegg, Lukas; Mato, Celia; Kueppers, Ulrich; Dingwell, Donald B.

    2016-04-01

    Pyroclastic density currents (PDCs) are a catastrophic transport mode of ground hugging gas-particle mixtures associated with explosive volcanic eruptions. The extremely high sedimentation rates and turbulence levels of these particulate density currents can freeze and preserve dynamic phenomena that happen but are not recorded in other sedimentary environments. Several intriguing and unanticipated features have been identified in outcrops and reproduced via analogue experiments, with the potential to change our views on morphodynamics and particle motion. Three types of small-scale (ca. 10 cm) erosion structures were observed on the stoss side of dune bedforms in the field: 1) vertical erosion planes covered with stoss-aggrading, vertical lamination, 2) overturned laminations at the preserved limit of erosion planes and 3) loss of stratification at erosion planes. These features are interpreted to indicate rapidly evolving velocities, undeveloped boundary layers, and a diffuse zone rather than a sharp border defining the flow-bed interface. Most experimental work on particle motion and erosion from the literature has been accomplished under constant conditions and with planar particle beds. Here, in order to reproduce the field observations, short-lived air-jets generated with a compressor-gun were shot into stratified beds of coarse particles (300 μm) of low density (1000 kg/m3). These "eroding jets" were filmed with a high speed camera and the deposits were sectioned after the experiments. The three natural types of erosion characteristics were experimentally generated. Vertical erosion planes are produced by small-scale, relatively sustained jets. Overturned laminations are due to a fluidization-like behavior at the erosion front of short-lived, strong jets, demonstrating that the fluid's velocity profile penetrates into the deposit. Loss of lamination seems related to the nature of erosion onset in packages. Rather than providing simple answers, the dataset

  20. Oxygen transport in the internal xenon plasma of a dispenser hollow cathode

    Energy Technology Data Exchange (ETDEWEB)

    Capece, Angela M., E-mail: acapece@pppl.gov; Shepherd, Joseph E. [California Institute of Technology, Pasadena, California 91125 (United States); Polk, James E.; Mikellides, Ioannis G. [Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, California 91109 (United States)

    2014-04-21

    Reactive gases such as oxygen and water vapor modify the surface morphology of BaO dispenser cathodes and degrade the electron emission properties. For vacuum cathodes operating at fixed temperature, the emission current drops rapidly when oxygen adsorbs on top of the low work function surface. Previous experiments have shown that plasma cathodes are more resistant to oxygen poisoning and can operate with O{sub 2} partial pressures one to two orders of magnitude higher than vacuum cathodes before the onset of poisoning occurs. Plasma cathodes used for electric thrusters are typically operated with xenon; however, gas phase barium, oxygen, and tungsten species may be found in small concentrations. The densities of these minor species are small compared with the plasma density, and thus, their presence in the discharge does not significantly alter the xenon plasma parameters. It is important, however, to consider the transport of these minor species as they may deposit on the emitter surface and affect the electron emission properties. In this work, we present the results of a material transport model used to predict oxygen fluxes to the cathode surface by solving the species conservation equations in a cathode with a 2.25 mm diameter orifice operated at a discharge current of 15 A, a Xe flow rate of 3.7 sccm, and 100 ppm of O{sub 2}. The dominant ionization process for O{sub 2} is resonant charge exchange with xenon ions. Ba is effectively recycled in the plasma; however, BaO and O{sub 2} are not. The model shows that the oxygen flux to the surface is not diffusion-limited; therefore, the high resistance to oxygen poisoning observed in plasma cathodes likely results from surface processes not considered here.