Study of the non-thermal character of electron distribution functions in the solar wind

0381860 - ÚFA 2013 FR eng D - Dizertace
Štverák, Štěpán
Study of the non-thermal character of electron distribution functions in the solar wind.
Universite Paris VI, Ecole Doctorale Astronomie et Astrophysique d'Ile de France. 11.05.2009. - Paris: Universite Paris VI, 2009. 88 s.
Výzkumný záměr: CEZ:AV0Z30420517
Klíčová slova: solar wind * plasma instabilities * non-thermal distribution functions
Kód oboru RIV: BL - Fyzika plazmatu a výboje v plynech

The non-thermal features of electrons observed in solar wind plasmas are analysed based on a statistical study of a substantial amount of measured electron velocity distribution functions (eVDF). The complete data set used in the present study was acquired in the low ecliptic latitudes covering the heliocentric distance from 0.3 up to 4 AU on board four different spacecraft, namely Helios I&II, Cluster II and Ulysses. Electron parameters are estimated by fitting of measured eVDFs with a novel model proposed to describes all three components of the solar wind eVDFs (i.e. the core, the halo and the strahl) analytically. The main goals achieved in the present work are (i) detail description of the radial evolution of main eVDF characteristics, i.e., the density, the temperature and the heat flux, with increasing heliocentric distance; and (ii) study of the effect of possible mechanism which can provide some additional heating or energy dissipation to solar wind electrons and moderate thus the shape of observed eVDFs during the solar wind expansion. Our findings indicate indirect evidences of scattering of strahl electrons into halo tails and the results also show the increasing deviations of eVDF non-thermal tails with increasing heliocentric radial distance. Furthermore, we show that both, kinetic plasma instabilities and Coulomb collisions, impose effective constraints on observed electron temperature anisotropies of the core component and also on the observed total electron heat flux.
Trvalý link: http://hdl.handle.net/11104/0212234