Fog and Space Charge

In a cloud chamber of 25 m3, the precipitation of a fog, composed of water droplets smaller than 20 ¿m in diameter, was investigated. Electrostatic charge was introduced through a corona discharge (between a thin wire or two wires of opposite polarity and a large grounded plane) pulse lasting from 0.2 to 1 second. Experiments have shown that the fog is unaffected by small electric charge. The modification occurs only when the droplets charge exceeds some critical value, about 10-16C for droplets of a diameter between 10 and 20 ¿m. Unipolar charge greater than 3 ¿C slightly increased the fog precipitation. Bipolar charges on the other hand accelerated the precipitation. This effect was well pronounced with charge content (of both signs) above 6 ¿C.