Langmuir probe diagnostic for measurement of recombination rates of positive ions with electrons in stationary afterglow system

We attempted to compare several probe theories that described collection of charged particles by Langmuir probe at elevated pressures. We used stationary afterglow environment with well-defined ionic composition to measure the electron density as a function of time. Afterglow plasma has the advantage that probability of secondary electron emission from probe surface when the probe works in positive ion acceleration regime is negligible and hence the probe data are more dependable. Since estimation of the rate of recombination required knowledge of absolute values of plasma density, we were able, in case of the ions the rate of recombination of which was known, to calculate the electron density, which corresponded to the known rate of recombination. Consequently we were able to compare apparent electron density calculated from the probe data using different theories with the "reference" electron density that we obtained from the known rate of recombination. Up to several mbar pressure the differences between the "reference" value of electron density and value calculated using the collisionless theories of electron collection by Langmuir probe stay within reasonable error limits. (C) 2004 Elsevier Ltd. All rights reserved.