極低温ヘリウムガス中におけるコロナ放電とイオン流場の特性

抄録

DC corona discharge in gaseous helium under non-uniform electric fields down to 4.2K at atmospheric pressure has been investigated. Although helium is a non-electro negative gas, a negative pulse corona is observed only near the normal boiling point and then negative breakdown voltage increases remarkably. Positive ion space charge modifies the electric field distribution in the gap space considerably. Criteria for corona inception and positive breakdown preceded by corona are proposed, and their availability is confirmed experimentally. The electric field strength, corona current density and space charge density are measured successfully and are analyzed theoretically using a bias probe method and a numerical field calculation technique. Apparent mobilities of charge carriers generated by positive and negative corona discharge are obtained with these discharge parameters. As a result, it is suggested that major ion species in positive corona is He⁺, and that an electronic bubble plays an important role in the negative pulse corona development near the normal boiling Point.