Measurement of the cross spectrum of random linear electrostatic waves in an isotropic Maxwellian plasma

Abstract

An experimental study is presented of the cross-power spectrum of the random high-frequency signals received by two small dipole antennas immersed in a stable, isotropic and collisionless plasma. These signals are due to the high-frequency microfield, i.e., to the random linear electrostatic wave field excited by the thermal motion of the electrons. For a Maxwellian plasma, the cross spectrum exhibits a main resonance peak slightly above the plasma frequency, and from this spectrum the electron density and temperature can be determined. The experiment has been performed in a laboratory plasma near thermal equilibrium. The results are in agreement with the theory, and show that the cross spectrum is very sensitive to any departure of the plasma from thermal equilibrium.