Sondage Des Plasmas Par Des Mesures D'Impedance

Abstract

1) The ionized wakes of hypervelocity pellets are investigated by the resonant cavity method (TM010, 250 Mcs). The input admittance of the cavity is measured with a four-probe admittancemeter, providing a XY - trace together with a SMITH chart on an oscilloscope CRT. Two methods are suggested to make the measurement time - resolved. From the two measured parameters (real and imaginary part of the admittance), the plasma parameters (total number N of electrons within the cavity and electron collision frequency ν) are deduced, owing to an energy perturbation theory, which is described. Discussions are included about accuracy, calibration methods and limitations. 2) The same apparatus is used to probe shock - ionized air in a coaxial shock-tube. The propagation of 250 Mcs waves is studied by this way.