Measurement of voltage and current in continuous and pulsed rf and dc glow discharges

Electrical measurements are an important tool for the characterisation of glow discharges and have proved to be useful for a variety of needs in fundamental studies and as control parameter. Therefore, extensive hardware developments and studies of current-voltage (I-U) characteristics in continuous and pulsed, dc and rf modes have been made [I] and will be presented together with new results. In continuous dc mode, the I-U curves are non-linear and may be characterised by a threshold voltage U-0 and saturation current I-max (both cathode material and pressure dependent). On the other hand P-U curves are to a large extent linear and very similar in the continuous rf mode [2]. The ionic part of time resolved I-U curves of rf discharges however shows almost a linear behaviour and the capacitive component is small. This led to the assumption that gas heating is responsible for the non-linearity between I and U in continuous dc discharges. Consistent with this assumption, a dependence of the I-U curves of pulsed discharges on the duty cycle was found. The comparison of the curves with those at low duty cycle (cold) led to a rough estimation of the gas temperature. Further investigation and cooperation with modelling groups is needed and planned to explain these results.