Self-Sharpening of Thin Tungsten Electrode in Single, High-Current Discharge: Its Dynamics and Mechanism

Self-sharpening of a thin tungsten electrode occurs in single, high-current discharge. This phenomenon has been observed with a custom-made, high-speed imaging system. The system allowed us to take one hundred images of the electrode shape during and after the discharge with 16 μs intervals. The following selfs-harpening mechanism has been proposed based on observations: (1) During the discharge, when the melt front descends towards the axis of the electrode, while the melt forms a sphere and moves along it due to the surface tension. (2) The melt continues moving even after the discharge, revealing a needle-shaped unmelted part and then solidifies. Detailed studies of discharge conditions to the diameter of the needle-shape formed by the process have been carried out. Results supporting the proposed mechanism are obtained.