Journal article
An improved sheath impedance model for the Van Allen Probes EFW instrument: Effects of the spin axis antenna
Journal of geophysical research. Space physics, Vol.122(4), pp.4420-4429
04/2017
DOI: 10.1002/2016JA023597
Abstract
A technique to quantitatively determine the sheath impedance of the Van Allen Probes Electric Field and Waves (EFW) instrument is presented. This is achieved, for whistler mode waves, through a comparison between the total electric field wave power spectra calculated from magnetic field observations and cold plasma theory and the total electric field wave power measured by the EFW spherical double probes instrument. In a previous study, a simple density‐dependent sheath impedance model was developed in order to account for the differences between the observed and calculated wave electric field. The current study builds on this previous work by investigating the remaining discrepancies, identifying their cause, and developing an improved sheath impedance correction. Analysis reveals that anomalous gains are caused by the spin axis antennas measuring too much electric field at specific densities and frequencies. This is accounted for in an improved sheath impedance model by introducing a density‐dependent function describing the relative effective length of the probe separation, Leff, in addition to the sheath capacitance and resistance values previously calculated. Leff values vary between between 0.5 and 1.2, with values >1 accounting for the anomalous gains and values <1 accounting for the shorting effect at low densities. Applying this improved sheath impedance model results in a significant increase in the agreement level between observed and calculated electric field power spectra and wave powers over the previous model.
Key Points
Anomalous gains identified to be caused by the spin axis antennas of Van Allen Probes EFW, occurring in specific plasma density range
Improved model is developed in order to account for these gains; same technique may be applied to other spacecraft (e.g., MMS)
Improved sheath impedance model is demonstrated to be extremely close to the maximum accuracy achievable using this new technique
Details
- Title: Subtitle
- An improved sheath impedance model for the Van Allen Probes EFW instrument: Effects of the spin axis antenna
- Creators
- D. P Hartley - University of IowaC. A Kletzing - University of IowaW. S Kurth - University of IowaG. B Hospodarsky - University of IowaS. R Bounds - University of IowaT. F Averkamp - University of IowaJ. W Bonnell - University of California, BerkeleyO Santolík - Charles UniversityJ. R Wygant - University of Minnesota
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.122(4), pp.4420-4429
- DOI
- 10.1002/2016JA023597
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 1
- Grant note
- Praemium Academiae JHU/APL (921647) NASA Prime (NAS5-01072; LH14010; LH15304)
- Language
- English
- Date published
- 04/2017
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199793702771
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