The measurement of ion mobility by using an axisymmetric ion-flow anemometer

The mobility of a negative ion cloud generated in atmospheric and in reduced air pressure was measured with an axisymmetric configuration of an ion-flow anemometer. The measuring apparatus consists of an emitter assembly, a collecting plate and a detecting ring. When a high voltage pulse was applied to the emitter assembly, an ion cloud was emitted and moves toward the collector. One of the results previously obtained was that the mobility of ion cloud changes with the amount of charge emitted, contrary to the constant value as customary believed. This experiment was further pursued by changing various parameters, such as electrode configuration and applied voltage. The amount of emitted charge from the emitter assembly can be varied by changing applied pulse voltage and/or pulse duration. The experimental results indicated that the mobility of ion increased with the amount of emitted charge and the extrapolated value to zero-charge agreed well with the published data. The values of mobility for different air condition, varying pressure and humidity were experimentally obtained. It was also shown that the mobility increases with the decreases of pressure and when humidity increases, the amount of charge emitted decreases, resulting in the reduced mobility.