HR: 0800h
AN: SM51A-0273    [Abstracts]
TI: Influence of Plasma Wake Around Satellite Body on Characteristics of Electric Field Sensor
AU: * Higashi, R
EM: higashi@ishikawa-nct.ac.jp
AF: Department of Electrical Engineering, Ishikawa National College of Technology, Kitacyujo, Tsubata, Kahoku-gun, 929-0392, Japan
AU: Imachi, T
EM: imachi@kenroku.kanazawa-u.ac.jp
AF: Information Media Center of Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
AU: Yagitani, S
EM: yagitani@is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science & Technology, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan
AB: Knowledge of the characteristics of wire antennas in magnetized plasma used as sensors for electric field observations by scientific satellites in geospace is necessary to determine the absolute intensity and the phase of the electric field wave because the observation data about electric field are available as voltage signal. Two important characteristics are the effective length and the antenna impedance. Determination of the impedance can be especially difficult since the impedance depends on the medium surrounding the antenna, and the impedance is affected primarily by the plasma sheath created around the antenna. The impedance of the antennas onboard Geotail was measured by Tsutsui et al. by using the calibration function onboard Geotail where a modulated square wave test signal was applied to the antenna elements. They found that the impedance depended mainly on the electron density and the satellite spin. The dependences of the impedance measurement on the satellite spin are caused by the fluctuation of the photoelectron emissions from the antenna surfaces. On the other hand, the impedance onboard Akebono was measured by Hashimoto et al., where the results also depended on the electron density and the satellite spin. However the photoelectrons do not play an important role in the impedance measurement, because the spin axis of Akebono always points to the sun. In this study, according to analysis of measurement results on Akebono, the dependence of the impedance on the angle between the antenna and the direction of satellite movement were found. Considering this phenomenon, the plasma wake is made around Akebono, and the impedance is changed by the electron density change near the antenna caused by the satellite spin. And the theoretical calculation result of the impedance assuming the electron density distribution around the spinning satellite body and the measurement result ware compare.
DE: 0609 Antennas
DE: 0634 Measurement and standards
DE: 0654 Plasmas
DE: 0694 Instruments and techniques
DE: 2712 Electric fields (2411)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting