Effect of the dielectric on the electron density measurement by hairpin probe

摘要

The floating microwave resonance probe, known as the hairpin probe, is a simple and straight forward technique for measuring the plasma density in a wide range of plasma configurations. It has been shown that sheaths forming around the hairpin's prongs can viciate the results. In this article is presented a model which takes into account different dielectric regions around the hairpin prongs for a more accurate plasma density measurement. Based on this model a new hairpin is designed. The new probe has the prongs covered with dielectric, which improves the mechanical strength and increases the lifetime of the probe specially in reactive plasmas. An experimental verification of the model is described. The hairpin's prongs are immersed in various quartz sleeves with different thicknesses and the effect of the dielectric coating on the resonance frequency is studied. Applying the model, the effective electron density measurements are compared with results obtained with a non-coated probe.