Influence of suprathermal electrons upon the transfer impedance of a quadrupolar probe in a plasma


  • Réjean Grard


Measuring the coupling impedance of two dipoles in a plasma is a diagnostic technique which has been used with success for several decades in space and in the laboratory. The plasma density and temperature are directly derived from the transfer impedance in a thermalized plasma, but the interpretation of the measurements is not as straightforward in the presence of suprathermal electrons. The purpose of this analytical work is to evaluate the transfer impedance of a quadrupolar array in the presence of two electron populations with different densities and temperatures. Such plasma mixtures are encountered not only in planetary environments but also in the close vicinity of cometary nuclei. It is concluded that it is possible to characterize the properties of the thermal electrons with a reasonable accuracy (≃10%) using an array with dimensions about 10 times the Debye length, even in the presence of a suprathermal population with a temperature 50–100 times larger and a comparable density.