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Nonhelical inverse transfer of a decaying turbulent magnetic field

Nonhelical inverse transfer of a decaying turbulent magnetic field. Cosmological magnetic fields Turbulent decay Nonuniversality of MHD Weak and strong turbulence Helical, nonhelical, hydro. Axel Brandenburg (Nordita  CU Boulder ). w ith T. Kahniashvili and A. Tevzadze.

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Nonhelical inverse transfer of a decaying turbulent magnetic field

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  1. Nonhelicalinversetransfer of a decayingturbulentmagneticfield Cosmological magnetic fields Turbulent decay Nonuniversality of MHD Weak and strong turbulence Helical, nonhelical, hydro Axel Brandenburg (Nordita  CU Boulder) with T. Kahniashvili and A. Tevzadze PRL 114, 075001 (2015)

  2. Motivation Early universe Energy momentum tensor Conformal time, rescaled equations

  3. Helical vs nonhelical 3-D decay helical vs nonhelical Initial slope E~k4 Christensson et al. (2001, PRE 64, 056405)

  4. Helical decay law:Biskamp & Müller (1999)

  5. BKT1

  6. Weak MHD turbulence, because B strong Lee, Brachet, Pouquet, Mininni, Rosenberg (2010)

  7. Inverse transfer similar to helical MHD Nonhelical gain ½ of helical case Gain from SS B Mediated by LS u Kinetic gain From B field

  8. Scaling relations

  9. Does initial spectrum determine decay?

  10. Rescaled spectra: self-similar Alternative interpretation of Olesen’s scaling relation Christensson et al. (2001, PRE 64, 056405) Initial slope E~k4

  11. Revised interpretation with integral scale x and q determined by physics from dimensional arguments

  12. Scaling relations

  13. Conclusions • Helicity slows down decay • Large scale energy increases • Nonhelical inverse transfer • Revised interpretation to Olesen • Self-similar spectra • Confirmed now by others (Berera & Linkmann 2015 Zrake 2015)

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