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Multifrequency Method for Measuring Properties of Shock Tube Produced Plasma

A novel multifrequency method is introduced in this paper for measuring the plasma produced by a Φ800-mm shock tube. The core of the measured object is a volume of relatively uniform plasma contained by the rectangular test section, and the dual-frequency or multifrequency configuration of the measuring system enables the coherent cancellation of measurement deviations. Based on the Lorentz model of plasma, the obvious correspondence exists between the plasma parameters and the transmittance variation with different frequencies of the electromagnetic wave; hence, the electron density Ne and the collision frequency ν of the plasma could be retrieved according to the measured transmittance. A dual-frequency system is established as the verification of the proposed method. The measured values of the electron density by the proposed method are compared with those obtained by other means, and the results are in good agreement.