RADIO FREQUENCY ION SOURCE

摘要

An rf ion source suitable for low power operation over a range of pressures in air comprises discharge electrodes having one or more cathodes (1) and an anode (2). Each cathode (1) is connected to an rf signal supply (8) through an associat ed coupling means (4) and the anode (2) is adapted to provide a surface area over which a plasma discharge may occur that is not substantially greater than the total cathoda l area over which the discharge may occur. In this way the anode (2) presents no more useful surface than is required to accommodate the optimum area of the plasma discharge thereby preventing plasma wander and enhancing the stability of the discharg e over known ion sources. By configuring the electrodes such that the respective areas of the anode and the cathode(s) over which discharge occurs are separated by no mor e than 5 mm and by forming the electrodes to have highly curved ends and so creating a higly distorted electric field in the inter-electrode gap when the source is in operation, it is possible to create an effective discharge with very low power input even at atmospheric pressure.