Measurement of Plasma Properties from the Cross Spectrum of Thermal Density Fluctuations

The relation between the density cross-correlation function and the cross spectrum of fluctuations in the electron saturation currents drawn by two Langmuir probes is used to measure basic plasma properties. The measured quantities using this approach are the ambipolar diffusion coefficient and the electron density. It is found that the method has sufficient sensitivity to determine changes in the ionic composition. These measurements are compared with plasma parameters obtained by using conventional probe techniques. Discrepancies are shown to exist and the source of these discrepancies is discussed.