Effect of charge exchange ions upon Langmuir probe current

The ion current to a Langmuir probe in low-density partially ionized plasma is enhanced by the collection of ions originating from charge-exchange collisions in the probe sheath. This enhancement is modeled by finding the volume integral of the charge-exchange rate in the sheath weighted by the probability that the slower charge-exchange ions are collected. Experiments in a hot-filament argon discharge show that the current enhancement and its dependence upon neutral pressure, plasma density, and probe bias voltage agree well with the model. (C) 2002 American Institute of Physics.