Electron Density Range Measurable by Microwave Resonator Probe with Higher Mode Resonance

摘要

A microwave resonator probe is a simple tool for measuring the electron density of 10~(10)-10~(12)cm~(-3) based on the plasma-induced shift △f in the resonance frequency of a U-shaped wire antenna. However, when the electron density is as low as 10~8-10~(10)cm~(-3), the measurement becomes difficult because of the small △f (low-density limit), and partly because of the reduction in resonance signal amplitude (high-density limit). Here, the measurable electron density range for the given antenna length is elucidated by taking into account these limitations and the instrumental limit of the network analyzer system used in the measurement. To expand the measurable electron density range to measure lower densities, we propose the use of the second-harmonic resonance. In addition to the analysis of the measurable electron density range, the experiments using the harmonic resonance are presented in terms of the electron density dependences on the discharge power and pressure in a surface wave plasma at 2.45 GHz.