Extraction of ions from a mercury arc plasma

Abstract

Ions and electrons are extracted from a mercury arc plasma through a hole of 0.1 cmø × 0.15 cm on a discharge anode. The applicability of the 3 2 - power law to the ion (Hg +) flow is examined. The ion current was between 0.17 and 7.4 μA and the apparent beam length was varied from 0.35–1.15 cm. While the electron beam extracted from the plasma obeys the 3 2 - power law fairly well, the mechanism of the ion extraction is quite different from that of the electron extraction. Between the normal plasma region and the pure ion beam, there is considered to be a transition or disturbed plasma region. The ions are emitted from the normal plasma and on passing through the transition plasma region where positive space charges are neutralized, a space charge limited ion beam is formed. Therefore, the 3 2 - power law can not be applied directly to the apparent ion beam from the plasma.