An analysis of the instability phenomena of a low current vacuum arc for copper cathode

A cathode spot model is used to analyze the instability phenomena of vacuum arc. The current below which no real solution exists is believed to be an unstable region. When the current decreases below 12 A, the electrons returning to the sheath region from the plasma region were found to dominate over positive ions, and thus the cathode electric field has an imaginary solution. An electrostatic probe was used to confirm these findings, and the analytical results were found to be similar to the measurement results. The present cathode spot model may be valid for volatile materials.