Investigation of plasma diagnostics using a dual frequency harmonic technique

Abstract

Plasma diagnostic methods using harmonic currents analysis of electrostatic probes were experimentally investigated to understand the differences in their measurement of the plasma parameters. When dual frequency voltage (omega(1); omega(2)) was applied to a probe, various harmonic currents (omega(1); 2 omega(1); omega(2); 2 omega(2); omega(2)+/-omega(1); omega(2)+/- 2 omega(1)) were generated due to the non-linearity of the probe sheath. The electron temperature can be obtained from the ratio of the two harmonics of the probe currents. According to the combinations of the two harmonics, the sensitivities in the measurement of the electron temperature differed, and this results in a difference of the electron temperature. From experiments and simulation, it is shown that this difference is caused by the systematic and random noise.