Simulation of resistive microwave resonator probe for high-pressure plasma diagnostics

A U-shape probe for microwave resonance in plasma was investigated in a range of high pressure (10-760 Torr). The electromagnetic field finite difference time domain-simulation of the probe revealed that, in the resistive resonance at high pressure, the resonant frequency fr approaches the dipole-antenna resonance frequency in vacuum, with almost no dependence on the electron density ne. However, the resonance width Deltaf is sensitive to the pressure, showing the maximum value at ~20 Torr. The normalized resonance width (Deltaf/fr) corrected by the one of vacuum value (no plasma) is linearly proportional to ne, and inversely proportional to num (electron-molecule collision frequency) for high-pressure plasmas. These simulation results are successfully explained in a model of two-conductor transmission line in cold collisional plasma. According to the resonance analysis, the methods for measuring the electron density and the electron collision frequency at high pressures (, ) were proposed.