RF impedance measurements of DC atmospheric micro-discharges
  The available diagnostics for atmospheric micro-plasmas remain limited and relatively complex to implement; so we present a radio-frequency technique for diagnosing a key parameter here. The technique allows one to estimate the dependencies of the electron density by measuring the RF-impedance of the micro-plasma and analyzing it with an appropriate equivalent circuit. This technique is inexpensive, can be used in real time and gives reasonable results for argon and helium DC micro-plasmas in holes over a wide pressure range. The electron density increases linearly with current in the expected range consistent with normal glow discharge behavior. 
Lawrence J. Overzet (PSAL), D. Jung, Monali Mandra (PSAL), Matthew   Goeckner (PSAL), Thierry Dufour (GREMI), Remi Dussart (...
physics.plasm-ph