A Sheath Impedance Model for the Van Allen Probes EFW Instrument

0497707 - ÚFA 2019 BE eng C - Konferenční příspěvek (zahraniční konf.)
Hartley, D. P. - Kletzing, C. A. - Kurth, W. S. - Hospodarsky, G. B. - Bounds, S. R. - Averkamp, T. F. - Bonnell, J. W. - Santolík, Ondřej - Wygant, J. R.
A Sheath Impedance Model for the Van Allen Probes EFW Instrument.
2 nd URSI AT-RASC Proceedings. Gent: URSI, 2018.
[URSI Atlantic Radio Science Meeting (AT-RASC) /2./. Gran Canaria (ES), 28.05.2018-01.06.2018]
Institucionální podpora: RVO:68378289
Klíčová slova: magnetospheric plasma * antenna sheath impedance * Van Allen Probes * EFW * EMFISIS * whistler mode waves
Obor OECD: Fluids and plasma physics (including surface physics)
http://www.ursi.org/proceedings/procAT18/papers/DHartleyURSIATRASC2018SummaryPaper.pdf

A technique to quantitatively determine the variable
coupling impedance between the Van Allen Probes
Electric Field and Waves (EFW) instrument and the
ambient magnetospheric plasma is presented. This is
achieved by applying the cold plasma dispersion relation
to whistler-mode chorus waves and plasmaspheric hiss. It
is then possible to perform comparisons between the
electric field wave power spectra predicted by cold
plasma theory (using magnetic field observations), and
the electric field wave power measured by the EFW
spherical double probes instrument. Investigation of the
ratio between observed and calculated wave powers, as a
function of frequency and plasma density, reveals a
structure consistent with signal attenuation via the
formation of a plasma sheath around the electric field
sensors. Further analysis reveals that anomalous gains
can occur at specific densities and frequencies due to the
shorter spin-axis antennas measuring too much electric
field. Antenna shorting effects are also apparent in the
low-density regime. A density-dependent model is
developed in order to quantify these effects. This sheath
impedance model allows for the sheath resistance, sheath
capacitance, and relative effective antenna length to be
quantified at any density frequently encountered on-orbit
and is demonstrated to be successful in significantly
improving agreement between calculated and observed
power spectra and wave powers.
Trvalý link: http://hdl.handle.net/11104/0290216