Enhanced production of multi-charged ions using pulse-modulated microwave in a 2.45 GHz electron cyclotron resonance source

Abstract

Fundamental phenomena of an electron cyclotron resonance (ECR) multi-charged 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 and potential well are formed near the bottom of the mirror trap. Multi-charged ions pass through the extractor at the mirror end, and the charge state distributions of extracted ions are investigated. Pulse-modulated microwave produces the ECR plasma with afterglow, relaxes the potential well, and then enhances the extracted multi-charged ion currents. Time-averaged Ar4+−9+ currents increase, even when the microwave power is nearly equal to or lower than the continuous microwave. The rectangular pulse width and the duty ratio are typically about 0.05 ms and 50%, respectively. The origin of enhanced production by pulse-modulated microwave is discussed by taking account of plasma parameters. Measurement of plasma parameters by a Langmuir probe and dependence of current increment on the ionic charge suggest the relaxation of the potential well.