Production of multiply charged ions by utilizing pulsed ECR plasma

Abstract

Fundamental phenomena of an electron cyclotron resonance (ECR) multicharged ion source (2.45 GHz) have been experimentally studied. The ECR plasma is confined in the mirror field superimposed by the octupole magnetic field. An ECR zone is formed near the bottom of the mirror trap. The multicharged ions pass through the extractor (10 kV) at the mirror end, and the charge state distributions of extracted ions are investigated. During the afterglow phase of the pulsed ECR discharge, multicharged ion currents are substantially higher than those during the heating phase of the plasma. The afterglow effect enhances time-averaged Ar/sup 4+-9+/ currents, even when the microwave power is nearly equal to or lower than the continuous microwave (cw mode). The shape and duration of the afterglow are investigated at various pressures and microwave powers. Optimum conditions for the different charge states are different. The pulse width and duty ratio are typically about 0.1 ms and 50%, respectively. The ion saturation current is measured by a Langmuir probe. The origin of enhanced production by these effects is discussed by taking account of plasma parameters and formation of plasma potential.