Noise Picked Up by External Probes in Electrodeless Gas Discharges

Noise and impedance measurements are reported for external electrodes wrapped around electrodeless discharges. For frequencies between 0.5 and 10 Mc/sec the equivalent noise temperature Tn of the probe noise lies between ½Te and Te, where Te is the electron temperature; this is attributed to the space-charge suppression of the ion shot noise flowing to the wall under the electrodes. At higher frequencies the noise temperature Tn increases because of a high frequency noise mechanism that is also present in dc discharges. The observed data can be fully interpreted in terms of what is known about the noise and impedance properties of floating probes in dc discharges.