114 大電流単発放電における電極形状変化の観察

概要

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Change of electrode shape occurs in high-current single discharge of a thin electrode : shape formed after discharge vary from a thinner needle for tungsten with negative polarity to a round ball for most of other electrodes. We have carried out time-resolved observation of the change using a high-speed imaging system during and after the discharge. The imaging system, which employs the second harmonics of a Q-switched Nd : YAG laser as an illuminating light, has a time resolution of 10ns and capable to observe the electrode shape through the bright arc plasma. We observe that tip of the electrode becomes molten state during the discharge and remains liquid state until hundreds of microseconds after end of the discharge. The melted electrode forms molten droplets, which move away from the tip along the electrode and induce the wear of the electrode length. They solidify eventually to determine the final electrode shape. Effects of discharge conditions to the shape change and the wear length are studied in some details.
2002-11-19