Neutralization of static surface charges by an ac ionizer in a nitrogen and dry air environment

To elucidate the dynamics of static charge elimination, we measured charge decay and residual potential (balance or offset voltage) in gases with various ion mobilities. It was observed that surface charge decay, especially for positive charges, occurs much faster in nitrogen than in air. The residual potential on the probe is negative in pure nitrogen and increases toward positive values with the injection of small quantities of air in front of the ionizer. The fluctuations in the residual potential are generally less than 3 V peak-to-peak. For ionizer operations in nitrogen environments, the charge decay rate increases with superficial gas-flow rate. The results are consistent with a theory of the interaction between bipolar ions and a charged object.