Modeling Transmission-Type Impedance Probes for Dusty Plasmas*

Impedance probes measure n_e and T_e by interpreting frequency-dependent transmission or reflection spectra (S₂₁ or S₁₁) of low-power RF signals (10^-5 W). These diagnostics are promising for use in dusty plasmas because they are less disruptive to plasma and dust than Langmuir probes, and easier and cheaper to implement than many common spectroscopic measurements, such as LIF. Capacitor-like, transmission-type impedance probes offer some further advantages over reflection-type probes because they can resolve plasma conditions near the probe vs farther away in the chamber, and because they also may be used a DC double Langmuir probe. One potential application is to measure the charge of a dust cloud by performing RF and DC measurements to measure n­_e and n_i, and using the quasineutrality condition, n_i - n­_e - n_d ≈ 0.

We model the probe-plasma system as a series of discrete circuit elements and use SPICE algorithms to simulate the transmission of RF signals through the plasma. We use these circuit simulations to measure plasma parameters from experimental impedance probe spectra collected in the DODECA and RaFyL plasma chambers at Auburn University.