Robust measurements of the electron-neutral collision frequency using plasma impedance probes
Introduction
One of the reliable and robust probes that have been used in several missions by NASA and other institutions is the Plasma Impedance Probe (PIP) (Balmain, 1964, Baker et al., 1966; Bishop and Baker, 1972, Oya, 1966; Oya and Aso, 1969, Oya and Obayashi, 1967; Oya and Morioka, 1975, Carlson, 2004, Ward et al., 2005, Ward, 2006, Blackwell et al., 2005a, Blackwell et al., 2005b, Blackwell et al., 2007, Spencer et al., 2008; Patra and Spencer, 2013; Spencer and Patra, 2015). The swept impedance probe (SIP), or RF impedance probe, or plasma impedance probe (PIP) is an electrically small antenna immersed in plasma by sweeping a sinusoidal voltage over a range of frequencies including the local plasma resonance frequency (), electron cyclotron frequency (), and the upper-hybrid frequency (). The most popular PIPs consists of an antenna that sweeps across the range of frequencies of the expected background plasma frequency. As the rocket/spacecraft passes through the ionosphere, based on the plasma parameters the antenna impedance encounters three resonance conditions that are associated with the electron plasma frequency, electron gyro-frequency, and electron-neutral collision frequency. This probe has proven measurement capabilities within the highly variable region of the ionosphere such as the Auroral zone (Abe et al., 2006, Wakabayashi and Ono, 2006, Jayram et al., 2008, Farr et al, 2014).
The measured current at the terminal results in distinct resonance regions in the input impedance curve associated with the local plasma parameters. The antenna input impedance in free space is capacitive at wavelengths much longer than the antenna dimensions. In the presence of plasma, the radiation characteristics of the antenna change. The plasma resonance parameters such , and produce a unique resonant peaks in the absence of plasma sheath.
The previous studies measured and estimated by tuning the plasma parameters in analytical and numerical models to fit with/against the PIP data (Ward et al., 2005, Spencer et al., 2008). They used the plasma fluid finite difference time domain PF-FDTD model developed originally at the Utah State University for their study. This approach has shown a close agreement between the value obtained using the PIP observations with the well-known empirical model (IRI model). The collision frequency values estimated by Spencer et al. (2008) were lower than the predicted values obtained by Shunck and Nagy in conjunction with MSIS 90 model. The previous sounding rockets have provided single measurement using 100 microseconds sampling rate and spatial resolution of 0.1 meters. The present work investigates the capability of using two different antenna types on the same payload to employ the discrepancy in the characteristic curves for improving the measurements. To investigate the proposed approach, the characteristic curve of the stacked patch and dipole antennas in the presence of a similar plasma environment is examined. The unique features in the impedance curve including the capacitive/inductive response to the surrounding plasma including various collisional plasma regimes are discussed. The possibility of narrowing down the electron-neutral collision frequency using the combined information obtained from simultaneous measurements of two antennas is elaborated. The capability of the proposed approach in the measurement of background neutral density is discussed. The aerodynamical effects of the rocket on the associated curve are studied. The possible impact of rocket rotation on the accuracy of neutral density measurement is investigated.
Section snippets
Computational model
The PF-FDTD model is incorporated in this study to explore the possibility of using dual antennas for robust ionospheric diagnostics. The model assumes a magnetized, and collisional plasma in the fluid approximations. The model solves Maxwell’s equations along with the plasma fluid equations. The simplified Maxwell’s equations combined with the continuity and momentum equations under the assumption of negligible compression term in the momentum expression, fluid current rolled into Ampere’s law
Conclusions
The plasma impedance probe is an instrument designed to measure local electron parameters in the ionospheric plasma. The immersed antenna in the plasma with varying input voltage across the antenna terminal will respond to the surrounding plasma through the variation of the exciting current at the terminal. The idea of using two antenna types as a plasma impedance probe on a sounding rocket and to improve the accuracy of measurements is proposed and investigated in this work. The impact of
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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