Low frequency bursts and ionization instabilities in weakly ionized plasmas

In this paper we report time dependent ion density bursts observed during the electron collection process from an unmagnetized plasma by a positively polarized electrode. For bias voltages over a threshold a double layer develops and the electron drained current exceeds the thermal levels. The energized electrons by the plasma potential voltage drop would excite a ionization instability in the plasma located at the high potential side, causing the subsequent fluctuations in the ion current downstream the double layer. These oscillations in the ion density were detected as abrupt decrements in the electron saturation current of a collecting Langmuir probe, located in Maxwellian background plasma, away form the double layer. The time elapsed between two successive jumps in ion density decreases with the amount of current drained by the metallic electrode. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)