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Magneto-rotational instability

Magneto-rotational instability. Axel Brandenburg ( Nordita, Copenhagen ). Discs and disc viscosity. Magnetorotational instability (MRI) how does it work? simulations and experiments Vertical stratification and radiation Heating near disc surface Star/disc coupling and outflows

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Magneto-rotational instability

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  1. Magneto-rotational instability AxelBrandenburg (Nordita, Copenhagen)

  2. Discs and disc viscosity • Magnetorotational instability (MRI) • how does it work? • simulations and experiments • Vertical stratification and radiation • Heating near disc surface • Star/disc coupling and outflows • Field lines open up, enhanced outflow

  3. Alfven and slow magnetosonic waves Vertical field B0 Dispersion relation Alfven frequency:

  4. Alfven and slow magnetosonic waves Alfven slow magnetosonic

  5. March 23, 1965: Gemini 3 Gus Grissom & John Young: docking with Agena space craft

  6. Analogy with tidal disruption, etc. Tidal disruption of a star Space craft experiment MRI (Balbus & Hawley 1991)

  7. Shearing sheet analysis with Boris Dintrans (Toulouse) linear analysis: variable wave number Rayleigh quotient

  8. Comparison withinviscid simulations Only reliable till t<18

  9. Shearing sheet simulations Dynamo makes its own turbulence Hyperviscosity 1283

  10. High resolution direct simulation singular! 5123 resolution

  11. Simulations with stratification cyclic B-field alpha-Omega dynamo? negative alpha

  12. Vertical stratification Brandenburg et al. (1996) z-dependence of

  13. Heating near disc boundary weak z-dependence of energy density where Turner (2004)

  14. Dan Lathrop’s new MRI experiment

  15. Dan Lathrop’s new MRI experiment

  16. Preliminary simulations W/2p = 48 Hz (WRi2/n = 375) 2000 G (Ha=146) 500 G (Ha=37) 1000 G (Ha=73)

  17. Pencil Code • Started in Sept. 2001 with Wolfgang Dobler • High order (6th order in space, 3rd order in time) • Cache & memory efficient • MPI, can run PacxMPI (across countries!) • Maintained/developed by many people (CVS!) • Automatic validation (over night or any time) • Max resolution so far 10243

  18. 256 processor run at 10243

  19. Wallclock time versus processor #

  20. CVS maintained • pserver (password protected) • Public (check-out only), private (ci/co, 20 people) • Set of 12 test problems • Nightly auto-test (different machines, web) • Before check-in: run auto-test yourself • Mpi and nompi dummy module for single processor machine (or use lam-mpi on laptops)

  21. Pencil Code check ins

  22. Intrinsic Calculation Ray direction Transfer equation & parallelization Processors Analytic Solution:

  23. Analytic Solution: Communication Ray direction The Transfer Equation & Parallelization Processors

  24. Analytic Solution: Intrinsic Calculation Ray direction The Transfer Equation & Parallelization Processors

  25. Current implementation • Plasma composed of H and He • Only hydrogen ionization • Only H- opacity, calculated analytically No need for look-up tables • Ray directions determined by grid geometry No interpolation is needed

  26. Disc and outflow (YSOs) Disc temperature relative to halo is free parameter: Here about 3000K Cooler disc: more vigorous evolution von Rekowskii et al 2003 (A&A)

  27. Unsteady outflow transport from disc into the wind BN/KL region in Orion: Greenhill et al (1998)

  28. Application: magnetic contamination of galaxy cluster 10,000 galaxies for 1 Gyr, 1044 erg/s each Similar figure also for outflows from protostellar disc

  29. Further experiments: interaction with magnetosphereAlternating fieldline uploading and downloading von Rekowskii & Brandenburg 2004 (A&A) Similar behavior found by Goodson & Winglee (1999) Star connected with the disc Star disconnected from disc

  30. Similar behavior found by Goodson & Winglee cf. field line opening: Uzdensky (2002), Pudritz & Matt (2004)

  31. Open questions • Radiation transfer with scattering • where • QPOs (vertical disc oscillation?) • In resonance with vert/rad epicycle freq? • Viscous instability

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