Impedance Probe Measurements in Dusty Plasmas

Impedance probes measure frequency-dependent transmission or reflection (S₂₁ or S₁₁) of low-power RF signals (10^-5 W), and the resulting spectra are interpreted to measure n_e and T_e. Impedance probes are a promising diagnostic tool for dusty plasmas because they are less perturbing to plasma and dust than traditional Langmuir probes. One potential use of impedance probes in dusty plasmas is to combine their measurements of n­­_e with an ion density measurement to measure the electric charge absorbed by a cloud of dust particles.

Transmission-type (S₂₁) impedance probes offer some advantages over reflection-type (S₁₁) probes in that they are separately sensitive to plasma near the probes and plasma farther away, and because the same probe tips may be used for double Langmuir probe measurements.

We present circuit simulations of such probes to investigate the interaction between probe tips, grounded chamber walls, bulk plasma, and plasma sheathes. We approximate the continuous plasma as a series of discrete circuit elements with values determined from a single-fluid plasma model. The results of these simulations are compared to experiments performed in a low temperature plasma.