Evidence of low-frequency oscillations in heavy ion plasmas heated by electron cyclotron resonance

Abstract

Time-resolved experiments (bremsstrahlung, diamagnetism, electron, and ion end-loss currents) have been carried out at the Electron Cyclotron Resonance Ion Source Quadrumafios [A. Girard, et al., Rev. Sci. Instrum. 65, 1714 (1994)] continuously operated with heavy neutral gases. All the diagnostics reveal oscillations (on the time scale of about 1 s) which could be characterized by variations of the hot electron perpendicular temperature. The onset of this low-frequency periodic regime with increasing heating powers and/or decreasing gas injection pressures is shown to limit the highly charged ion currents available. The addition of a lighter gas, e.g., He into Kr, delays the appearance of the periodic regime and enables one to extract higher currents.