Wave cutoff method to measure absolute electron density in cold plasma

Abstract

A method for precise measurements of absolute electron density in plasma using wave cutoff is described. This method of measurement uses a network analyzer with radiating and detecting antenna A microwave signal of 10 kHZ–3 GHz frequency is introduced into the plasma from a radiating port of the network analyzer and propagates in the plasma. The transmitted wave is monitored at a distance from a radiating antenna using an antenna connected to the receiving port of the network analyzer. The transmitted wave decays rapidly at a cutoff plasma frequency, which is a direct measure of the absolute electron density. This cutoff method is free of many difficulties often encountered with a Langmuir probe, such as thin film deposition and plasma potential fluctuation. The cutoff probe can also measure the spatial distribution of the electron density. The measurement technique is analyzed theoretically and experimentally, demonstrated in density measurements of an inductively coupled radio-frequency plasma, and is compared with the double probe and a plasma oscillation methods.