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Arc Cathode

The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform

X. Zhou – 1st expert on this subject based on the ideXlab platform

  • an experimental investigation of factors affecting Arc Cathode erosion
    Journal of Physics D, 1998
    Co-Authors: X. Zhou, J Heberlein

    Abstract:

    A specially designed thermal plasma reactor system for the investigation of ArcCathode erosion has been set up. By using an OMA-spectrometer system, emission spectroscopic measurements of electron temperature and electron number density in the Cathode region have been performed, together with single-colour and two-colour pyrometry of Cathode temperature distributions. Observation of Cathode spot behaviour has been carried out simultaneously by employing a telemicroscope and a high-speed vision system. Cathodes have been examined by SEM and EDX after Arcing. For pure tungsten Cathodes, the initial Cathode geometry has almost no effect on the Cathode spot’s behaviour due to the molten state of the Cathode spot. The major erosion mechanism is the ejection of liquid droplets from the Cathode spot. However, the initial Cathode geometry has a certain influence on the Cathode‘s erosion for 2% thoriated tungsten Cathodes. A highly non-uniform erosion pattern will occur if the Cathode is overcooled, probably due to ion bombardment in the low-temperature regions of the Arc-attachment spot.

  • Characterization of the Arc Cathode attachment by emission spectroscopy and comparison to theoretical predictions
    Plasma Chemistry and Plasma Processing, 1995
    Co-Authors: X. Zhou, Joachim Heberlein

    Abstract:

    Emission spectroscopic diagnostics of electron temperature distribution and electron number density distribution in the Cathode region have been carried out employing an OMA/spectrometer system. Single color and two color pyrometry of Cathode temperature distributions have also been performed. The experimental results are compared with results of a theoretical model formulated previously to study the Arc Cathode interaction.

  • Characterization of the Arc Cathode attachment by emission spectroscopy and comparison to theoretical predictions
    Plasma Chemistry and Plasma Processing, 1995
    Co-Authors: X. Zhou, J Heberlein

    Abstract:

    Emission spectroscopic diagnostics of electron temperature distribution and electron number density distribution in the Cathode region have been carried out employing an OMA/spectrometer system. Single color and two color pyrometry of Cathode temperature distributions have also been performed. The experimental results are compared with results of a theoretical model formulated previously to study the Arc Cathode interaction. The results show that the plasma in the Cathode region strongly deviates from LTE. Thermionic cooling is the major cooling mechanism of Cathodes at high Arc currents. The work function of 2% thoriated tungsten Cathodes increases during Arcing due to fast evaporation of thorium from 2% thoriated tungsten Cathodes.

B. Jüttner – 2nd expert on this subject based on the ideXlab platform

  • the retrograde motion of Arc Cathode spots in vacuum
    Journal of Physics D, 2000
    Co-Authors: B. Jüttner, Ingmar Kleberg

    Abstract:

    Experiments are reported on the retrograde Arc spot motion on copper and tantalum Cathodes in vacuum in the presence of a magnetic field. The spots are imaged with time and space resolutions of <100?ns and <10??m, respectively. The magnetic flux density amounted to B = 0.4?T and the Arc currents to 2-100?A. For times <1??s random displacement occurs on a time scale <100?ns. At intervals of about 4??s, jumps of the spot are observed over distances of 50-300??m in the retrograde direction, thus yielding macroscopic velocities of about 50?m?s-1. The jumps are preceded by the ejection of plasma jets in the retrograde direction, having average velocities of about v = 5?km?s-1. New spots are formed exactly in the jet direction. The jets are explained by instabilities in the magnetically confined spot plasma, and the spot formation by electric fields = ? within the jets. The jets are ejected in periods of enhanced plasma production caused by the inner spot processes, i.e., by the dynamics of fragments and cells, having diameters of ?20 and ?10??m, respectively. No reversal of the motion has been observed at elevated temperatures up to 2100?K.

  • The retrograde motion of Arc Cathode spots in vacuum
    Journal of Physics D, 2000
    Co-Authors: B. Jüttner, Ingmar Kleberg

    Abstract:

    Experiments are reported on the retrograde Arc spot motion on copper and tantalum Cathodes in vacuum in the presence of a magnetic field. The spots are imaged with time and space resolutions of

  • nanosecond displacement times of Arc Cathode spots in vacuum
    IEEE Transactions on Plasma Science, 1999
    Co-Authors: B. Jüttner

    Abstract:

    With a high speed camera consisting of a combination of framing and streak channels, Arc spots on a copper Cathode are imaged in the spectral range 200-800 nm with spatial and time resolution of to the observation time t of /t=(2.3/spl plusmn/0.6)/spl times/10/sup -3/m/sup 2//s. This holds down to t=100 ns. Thus, fragments and spots operate on nanosecond time scales. Prior to apparent spot splitting and after apparent fragment merging the spot brightness increases considerably. When analyzing time-integrated pictures, the stages of increased brightness lead to overestimating the average residence time. Because of the short formation time, the fragments do not reach a balance between surface heating and heat conduction into the bulk, i.e., there is no stationary evaporation. A further substructure of the fragments exists with size <5 /spl mu/m and timescale /spl les/10 ns.

J Heberlein – 3rd expert on this subject based on the ideXlab platform

  • an experimental investigation of factors affecting Arc Cathode erosion
    Journal of Physics D, 1998
    Co-Authors: X. Zhou, J Heberlein

    Abstract:

    A specially designed thermal plasma reactor system for the investigation of ArcCathode erosion has been set up. By using an OMA-spectrometer system, emission spectroscopic measurements of electron temperature and electron number density in the Cathode region have been performed, together with single-colour and two-colour pyrometry of Cathode temperature distributions. Observation of Cathode spot behaviour has been carried out simultaneously by employing a telemicroscope and a high-speed vision system. Cathodes have been examined by SEM and EDX after Arcing. For pure tungsten Cathodes, the initial Cathode geometry has almost no effect on the Cathode spot’s behaviour due to the molten state of the Cathode spot. The major erosion mechanism is the ejection of liquid droplets from the Cathode spot. However, the initial Cathode geometry has a certain influence on the Cathode‘s erosion for 2% thoriated tungsten Cathodes. A highly non-uniform erosion pattern will occur if the Cathode is overcooled, probably due to ion bombardment in the low-temperature regions of the Arc-attachment spot.

  • Characterization of the Arc Cathode attachment by emission spectroscopy and comparison to theoretical predictions
    Plasma Chemistry and Plasma Processing, 1995
    Co-Authors: X. Zhou, J Heberlein

    Abstract:

    Emission spectroscopic diagnostics of electron temperature distribution and electron number density distribution in the Cathode region have been carried out employing an OMA/spectrometer system. Single color and two color pyrometry of Cathode temperature distributions have also been performed. The experimental results are compared with results of a theoretical model formulated previously to study the Arc Cathode interaction. The results show that the plasma in the Cathode region strongly deviates from LTE. Thermionic cooling is the major cooling mechanism of Cathodes at high Arc currents. The work function of 2% thoriated tungsten Cathodes increases during Arcing due to fast evaporation of thorium from 2% thoriated tungsten Cathodes.

  • Model predictions of Arc Cathode erosion rate dependence on plasma gas and on Cathode material
    Proceedings of IEEE Holm Conference on Electrical Contacts, 1993
    Co-Authors: X. Zhou, J Heberlein, E. Pfender

    Abstract:

    We have previously reported results of a theoretical study which predict that high current Arc Cathode erosion is predominantly dependent on the work function and the vapor pressure of the Cathode material, and that the thermal design plays a secondary role. These results have been obtained with a newly developed self-consistent model of the Cathode region including a realistic one-dimensional sheath model. The results have been obtained for an argon Arc and a tungsten Cathode. The model has now been extended and results have been obtained for different Arc gases and different electrode materials. The Arc gas has a strong effect because it affects not only the temperature at the boundary between the Arc and the Cathode region, but also the electron density in the Cathode region and at the Cathode. The results of the calculations show that the Cathode material plays a dominant role in terms of the Cathode spot temperature and the associated mass loss rate by evaporation of Cathode material. Since the addition of thorium oxide to tungsten reduces the work function of the Cathode material, the Cathode spot temperature as well as the mass loss rate by evaporation are reduced. For the same Cathode material, hydrogen leads to the highest Cathode spot temperature and mass loss rate, followed by nitrogen and argon. The current density at the Cathode spot, the Cathode spot size, and the percentages of the energy fluxes removed from the Cathode spot are mainly determined by the plasma gas rather than by the Cathode material.