Determination of the complex dielectric constant, electric field and conductivity at the boundary of ionised gas

A method and boundary probe using an AC bridge as a sensor is described, by means of which the current density J, electric field E, conductivity ¿¿ and complex permittivity of an ionised gas may be determined at a point on its boundary. The probe itself is a three-terminal capacitor transformed into one flat plane, with typical diameters of 1 mm to 3 mm. Fitting flush with the electrode or vessel boundary, it has excellent positional discrimination because of its small size. Using a modern AF to RF transformer ratio bridge as the sensor, the several quantities may be measured to better than 5% for so lightly ionised a gas as a corona at NTP. The calibration is independent of space-charge density and carrier mobility. At low diagnostic frequencies below the relaxation frequencies for the ions or electrons under observation, the measurement essentially records DC values of ¿¿, E and J. The method is also suitable for use with electrolytes and powders.