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

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.