Plasma Physics Seminar ( Phys 769)

Dr. David Blackwell, Naval Research Laboratory

Plasma Impedance Measurements and Determination of Plasma Parameters

A small spherical probe is used in conjunction with a network analyzer to determine the impedance of the probe-plasma system over a wide frequency range. Impedance curves are in good agreement with accepted circuit models with plasma-sheath and electron plasma frequency resonances easily identifiable. Clear transitions between capacitive and inductive modes as predicted by the model are identified. Sheath thickness and absolute electron density are determined from the location of these transitions. The absolute electron density indicated by the location of the impedance resonance is compared to measurements using the plasma oscillation method.