Loading aerosols

摘要

An aerosol (20) entering through an inlet tube (22) is charged by an electrode ring (48) to produce unipolar ions. A radioactive source (38) produces bipolar ions to enclose the unipolar stream which is then guided along the axis of the loading tube. Alternatively unipolar ions are produced by corona discharge from an electrode (38). A number of sequential ring electrodes (46,47) are subjected to a ramped potential decreasing towards the exit of the aerosol (24) at an outlet tube (27), where the final ring is earthed. The field at the exit is arranged to be in the opposite sense the preceding field in order to concentrate the aerosol stream around the axis. The aerosol flows through a clean tube (52) that carries the electrode rings on the outside. The apparatus is particularly suitable for particles less than 20 nm in size.