Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Kinetics of solar wind expansion : simulations and observations

jeudi 23 octobre 2008, par Lorenzo Matteini (LESIA, Observatoire de Paris)

Mardi 28 octobre 2008 à 11h00 , Lieu : salle de confĂ©rence du bât. 17

Kinetic physics plays an important role in many space plasmas and the study of microsopic scales is often necessary to correctly understand the macrosopic dynamics of a system. In situ observations of the solar wind plasma show that particle velocity distribution functions are not Maxwellian and depart from the thermodynamical equilibrium. Proton distributions are characterized by the presence of a velocity beam and a temperature anisotropy with respect the ambient magnetic field ; these properties suggest that kinetic processes take place along the solar wind expansion. I will discuss the role of wave-particle and wave-wave interactions in the evolution of the solar wind protons : the effetcs of plasma kinetic instabilities, cyclotron heating and non-linear particle trapping are investigated using a hybrid numerical code which includes the effects of the expansion on the plasma. Simulation results are compared with direct observations of Helios and Ulysses spacecrafts in the distance range 0.3-2.5 AU, providing in reasonable agreement with solar wind data.