小電流真空アークの不安定現象の解析

抄録

In order to clarify the instability phenomena of a low current vacuum arc, characterized by noise on the current trace prior to the actual current chopping, an analysis of copper cathode spot has been made. For the analysis, cathode spot region is recognized as the collisionless space charge sheath connected with singly ionizad collisional plasmas.
It is proposed that a current level below that no real solution exists is unstable current and this current corresponds to the point at which a vacuum arc turns into unstable.
It is found that there is no real solution when the current is below 25A. The physical explanation is considered that the electrons returning to the sheath region from the plasma one dominate over positive ions and, consequently, the electric field at the cathode surface is F₀²≤0 below 25A.