Total electron temperature measurements in the solar wind with quasi-thermal noise spectroscopy
Abstract
The transport of the energy in space plasma, especially in the solar wind,is far from being understood. Measuring the temperature of the electrons and their non thermal properties must give important clues to understand the transport properties in collisionless plasma. Quasi-thermal noise spectroscopy is a reliable tool for measuring accurately the electron temperature since it is less sensitive to the spacecraft perturbations than particle detectors. We model the Quasi-Thermal Noise (QTN) with a generalized Lorentzian ("Kappa") distri-bution function defined by three parameters : the electron density and temperature, and the kappa index related to non-thermal properties of the medium. For collisionless and drifting plasma (like the solar wind), this noise is produced by the quasi-thermal fluctuations of the electrons and by the Doppler-shifted thermal fluctuations of the ions. A sum of two Maxwellian functions (one for the core and one for the supra-thermal halo) has previously been used for modelling the QTN of the electrons, but the observations have shown that the supra-thermal electrons are better fitted by "Kappa" distribution function. We show some generic properties of the QTN and give some practical consequences of using kappa distribution instead of a sum of two Maxwellian functions for plasma measurements. We apply this method to Ulysses/URAP data obtained during the first pole-to-pole fast lati-tudinal scan in the fast solar wind. These results will allow us to discuss the variations with heliocentric distance and latitude of the 3-fitted parameters : the electron density, the electron temperature and the kappa index of the distribution. Especially, the total electron temperature variation with distance during the solar minimum at high latitudes will be compared with the temperature profile predicted by a kinetic collisionless model of the solar wind.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.1903L