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Plasma density and temperature with Quasi-Thermal Noise Spectroscopy
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Data Set Overview
The Cassini Radio and Plasma Wave Science (RPWS) Quasi Thermal Noise (QTN) data set contains thermal plasma parameters derived by QTN spectroscopy analysis applied on data acquired with the High Frequency Receiver (HFR) during the perikrones of the entire mission. This data set includes the total electron density and the core electron temperature, as well as the uncertainties on the measurements. It also includes ancillary data about the location of the spacecraft at the time of the measurement: distance to Saturn, local-time, kronographic latitude and dipolar L-Shell apex distance. Data are presented in CDF files, which contain a 1D array depending on time for each parameter. This data set is intended to be the most comprehensive and complete data set for thermal plasma parameters measured by the HFR in the Cassini RPWS archive. A browse data set is included with these data which provides for a graphical search of the data using a series of thumbnail and full-sized plots which lead the user to the particular data files of interest.
This data set comprises spacecraft event time, radial distance (in Saturn Radii) from Saturn, latitude (in deg), local time (in hours) and L-shell (in Saturn Radii) of the spacecraft, total electron number density (in cm-3) with the measurement uncertainty, core electron temperature (in eV) with the measurement uncertainty and quality flag that were acquired by QTN analysis on RPWS/HFR Spectra.
The present data set was derived from the level two data of RPWS/HFR. The analysis was compiled by the LESIA team (Observatoire de Paris, Meudon, France).
The total electron density is deduced from a strong signal peak near the upper-hybrid resonance (FuH), independently of any calibration. Indeed, the plasma frequency Fp can be derived from the FuH resonance and the gyrofrequency Fg (derived from magnetic field measurements by the Cassini/MAG instrument [1]):
The total electron density Ne is then obtained as:
The error on the density was calculated on the basis of the uncertainty of the HFR receiver spectral relative resolution (df/f = 5%, 10% or 20%).
The core electron temperature is deduced from the thermal plateau level Vmin2 below FuH, given in [2] as a function of the core temperature Tc and Debye length LD (see Eq. 1 of [2]):
(using S.I. units), Vmin2 in V2/Hz. Here Fv(kL) is the Cassini V-shaped antenna response, with L the single wire length (L ~ 10m),
is the dipole antenna capacitance at low frequencies, with a the wire radius (a ~1.4 cm), and CB is the base capacitance. We then use an iterative method to deduce Tc.
The error on the temperature is determined a posteriori by estimating the averaged 1-sigma dispersion of the temperature level during the perikrone.
A full description of the methodology and results can be found in [3]
[1] Dougherty et al. 2004. [link]
[2] Moncuquet et al, 2005. [link]
[3] Schippers et al, 2013. [link]

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