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Arc Motion and Modes in a Homopolar Device.

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Final rept. Sep 67-Aug 69,

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The observed modes and the dynamic behavior of an electric arc in a homopolar device for constant current 100A and magnetic field 1,500G are quantitatively dependent on the type of gas He, Ne, Ar, Xe. The peculiar behavior of the arc for both electrode polarities can be explained as a result of a competition between geometrical flow effects and the Hall effect, with the latter becoming more pronounced with decreasing pressure. The well known tendency of the cathode spot to move into the retrograde direction at low pressures under the influence of a transversal magnetic field seems only of secondary importance. No steady retrograde motion of the arc column has been observed. The Hall voltage is used to explain quantitatively the measured dynamic arc voltage as function of pressure. For all gases investigated the measured Hall parameter 10omega0.4 is given as function of pressure and roughly proportional to 1p. Also, the arc rotational frequency as function of 1pM pgas pressure Matomic weight can be plotted as one curve, which suggests that for lower pressure the main loss is kinetic energy of the rotating gas which has to be replaced by the electromagnetic energy of the rotating arc. In summary, two distinct arc modes for low gas pressures can be defined depending on electrode polarity when the center electrode is cathode, the filamented current carrying arc moves together with the gas at high azimuthal velocity in amperian direction when the center electrode is anode the discharge becomes diffuse and stationary in regard to the laboratory and pumps the plasma with high speed in the azimuthal amperian direction. Author

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  • Plasma Physics and Magnetohydrodynamics

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