INFLUENCE OF SUPRATHERMAL ELECTRONS UPON THE TRANSFER IMPEDANCE OF A QUADRUPOLAR PROBE IN A PLASMA

Measuring the coupling impedance of two dipoles in a plasma is a diagn ostic technique which has been used with success for several decades i n 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 i n the presence of suprathermal electrons. The purpose of this analytic al work is to evaluate the transfer impedance of a quadrupolar array i n the presence of two electron populations with different densities an d temperatures. Such plasma mixtures are encountered not only in plane tary environments but also in the close vicinity of cometary nuclei. I t is concluded that it is possible to characterize the properties of t he thermal electrons with a reasonable accuracy (similar or equal to 1 0%) using an array with dimensions about 10 times the Debye length, ev en in the presence of a suprathermal population with a temperature 50- 100 times larger and a comparable density.