Using a direct current (DC) glow discharge electrode as a non-invasive impedance probe for measuring electron density.

A small RF signal is applied to the anode of a low pressure ( ≤ 200 mTorr), low temperature ( ≤ 3 eV) direct current (DC) glow discharge operating at an electron density of ∼ 10 cm. The discharge is modeled as a collection of capacitive, resistive, and inductive circuit elements that have resonances at particular frequencies, much like an RLC circuit. The location of these resonances in frequency space provides information about the plasma parameters.