IMPROVED ANALYTICAL METHOD FOR PLASMA ELECTRON DENSITY MEASUREMENT BY RESONANT CAVITY PERTURBATION THEORY

Abstract

A method of plasma density measurement based on microwave resonant cavity perturbation (by Kornegay (14)) is described. Resonant cavity theory was analyzed and a resonant cavity with special structure was designed for measuring the low density plasma. In the middle of the closed cavity, there were cut-ofi tubes which were extended a little into the cavity to get through the plasma. It was found that the distribution of the electrical fleld intensity was the densest near the cut-ofi tubes when the cylindrical cavity operating with TM010 mode. By using the method of resonant equivalent circuit analysis, both the amplitudes and phases of the Scattering matrices (S matrices) were obtained before the plasma came and at the time of the plasma passing through. Then the electron line density (Ne) and the electron-molecule collision frequency for momentum transfer (vm) were calculated. A modifled formula was proposed based on our simulation which was conducted in HFSS and experimental results. With the comparison of our results and Kornegay's, it was found that the accuracy of the plasma dielectric constant calculation was improved about 5 percent.