Measurement of plasma wave spectral density from the cross-power density spectrum

Abstract

Determination of the spectral density of plasma waves from the cross-power density spectrum is shown to be simpler than the alternative determination from the cross-correlation function. A device for measuring the cross-power spectral density is described in detail. A model with a bandwidth of 30 MHz has been constructed using integrated circuits, and applied to the study of ion acoustic wave propagation on a plasma positive column. Since it is an analog device, it should be possible to extend the bandwidth for operation into the gigahertz range. Only a fixed delay is required to measure the quadrature component of the cross-power spectral density. These features are in contrast to other correlators and cross-power spectrum analyzers described to date, which are either limited to the low megahertz range, or require a variable delay line.