Greifswald 2009 – wissenschaftliches Programm

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EP: Fachverband Extraterrestrische Physik

EP 7: Poster Session Extraterrestrics

EP 7.21: Poster

Dienstag, 31. März 2009, 17:30–19:00, Foyer der Zahnklinik

Large scale magnetic structure formation in 3D- MHD Turbulence — •Shiva Kumar Malapaka and Wolf-Christian Müller — Max-Planck -Institute for Plasma Physics, Garching bei München

Processes leading to the large scale magnetic structure formation from small scales in the universe are not yet clearly understood. Studies on one of the plausible processes namely inverse cascade of magnetic helicity in 3D- MHD turbulence, through direct numerical simulations is being reported here. The numerical simulation setup consists of an initial condition and a forcing placed in the small scales. Through the forcing we can introduce a fraction of magnetic helicity and or kinetic helicity over a band of wavenumbers in the small scales. In these simulations we observe power law behaviours in several quantities which hitherto are not known to show power law behaviours. We also observe different values to the power law exponents to the quantities, which were already known to show one. Only the total energy shows the expected k -5 / 3 power law behaviour, where k is the wavenumber. From the dimensional analysis of EDQNM(eddy damped quasi normal Markovian approximation) equations using these power laws , we obtain a relation EkM ~ (k2 HkM EkV ) / HkV , from which we infer that the increase in the magnetic energy( EkM) might be due to an interaction between the magnetic and kinetic helicities, where HkM, EkV, HkV respectively represent magnetic helicity, kinetic energy and kinetic helicity. This relationship is also valid for a purely decaying 3D MHD turbulence case , where the initial condition is placed in relatively larger scales. The importance of decaying turbulence in large scale magnetic structure formation is emphasised.