On diagnostics of space plasma with tubular dipole antenna

Abstract

Summary form only given. A concept of a good voltmeter is routinely applied to interpretation of electromagnetic wave spectra measurements (noise spectra) in space plasma. According to this concept, plasma density may be inferred from specific banded structure assigned to upper hybrid band. Good voltmeter concept is quantified by proximity of a transfer function of equivalent circuit to a constant value. Good voltmeter concept was inapplicable to interpretation of noise spectra registered on the ionospheric satellite Intercosmos-19 (IK-19). With plasma density derived from topside sounder data and equivalent circuit numerical simulation, it was shown that parameters of specific banded structure correspond to a parallel resonance. The parallel resonance follows from a preamplifier input capacitance and antenna inductance between electron cyclotron and upper hybrid frequencies, in cold magneto plasma approximation. In subsequent satellite projects (IK-24, IK-25, IK-27), noise and antenna impedance measurements were integrated in one instrument in order to have plasma density from two independent techniques. The presentation is aimed to elucidate relations among the most typical spectral structures in noise and impedance data, plasma density and equivalent circuit parameters, possibly influenced by spacecraft plasma interactions. Global consistency between plasma density signatures in noise and impedance data and those in simulations support statement that basic misinterpretations in broad set of data were avoided. Our data set is characterized by orbit inclination of ~80deg, altitude range of ~500 km-3000 km, frequency range of ~0.1 MHz-30 MHz and antenna length of 15 m. Despite limited applicability of the good voltmeter concept to interpretation of wave measurements in ionospheric electron plasma, it is show that plasma density can be deduced from parallel resonance and that resonance components can be separated from components of electromagnetic field in the vicinity of the antenna. To reach these goals, the preamplifiers with variable electrical parameters should be implemented and noise measurements should be integrated with independent technique capable to provide sufficiently accurate values of plasma density. Inherent relation to wave measurements, simplicity and absolute accuracy point antenna impedance measurements as complementary source of plasma density, required for interpretation, calibration and verification. Numerical simulations of radiospectrometer and impedance equivalent circuits are essential at instrument design and data analysis stages. A sample of simulations pertinent to long antennas in a magnetosphere is presented