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Global Simulations of Astrophysical Jets in Poynting Flux Dominated Regime

Global Simulations of Astrophysical Jets in Poynting Flux Dominated Regime. Engine; Injection; Collimation; Propagation; Stability; Lobe Formation; Dissipation; Magnetization of IGM. Hui Li S. Colgate, J. Finn, G. Lapenta, S. Li. Leahy et al. 1996. I. Engine and Injection.

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Global Simulations of Astrophysical Jets in Poynting Flux Dominated Regime

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  1. Global Simulations of Astrophysical Jets in Poynting Flux Dominated Regime • Engine; Injection; • Collimation; Propagation; Stability; • Lobe Formation; • Dissipation; • Magnetization of IGM Hui Li S. Colgate, J. Finn, G. Lapenta, S. Li

  2. Leahy et al. 1996

  3. I. Engine and Injection Approach: Global Configuration Evolution without modeling the accretion disk physics. Replace accretion disk with a “magnetic engine” which pumps flux (mostly toroidal) and energy.

  4. Mimicking BH-Accretion System? • Y : Initial poloidal fields on “disk”, exponential drop-off • f(Y): B profile, or disk rotation profile • a : toroidal/poloidal flux ratio • JxB :radial pinching and vertical expansion • JpxBp: rotation in  direction, carrying angular momentum? • Problems: • No disk dynamics • Footpoints allowed to move, though could be in equilibrium • Not precisely Keplerian • Mass loading? • Dipole or Quadrupole a=0.1 a=3 a=5 Li et al.’05

  5. Injection • Impulsive Injection: Evolution of a highly wound and compressed magnetic “spring” • Continuous Injection: Evolution of “magnetic tower” with continuous injected toroidal and/or poloidal fields An initial state modeled as a magnetic spring (=3). Toroidal field is added as a function of time over a small central region: Adding twists, self-consistently collimate and expand.

  6. II. Collimation; Propagation Run A: impulsive injection, =50 vinj >> vA > cs Run B: continuous injection, =3, =3 vA > cs, scanning through  (vinj)

  7. Run A |B| at cross-section

  8. Run A Total |B|

  9. Current density

  10. Run A Run A-2 Kinetic Magnetic Kinetic Magnetic

  11. III. Stability and Lobe Formation • Dynamic: moving, q-profile changing • 3D Kink unstable in part of helix: twist accumulation due to inertial/pressure confinement • Pressure profile: hollow • Velocity profile ?

  12. Pressure Evolution In Implusive Injection Case height radius

  13. Azimuthally averaged Poloidal Flux (n=0) 3D Flux Conversion height radius

  14. Azimuthally Averaged Poloidal Flux Continuous Injection height radius

  15. Run B: Continuous Injection Poloidal flux Y at disk surface Injected toroidal flux vs time

  16. T=0 B flux T=4 T=8 T=12 T=16 A Moving “Slinky” Z (height)

  17. T=0 T=3 T=10 T=5

  18. pressure Helix Stability height radius

  19. Lobe Formation

  20. Continuous Injection An initial state modeled as a magnetic spring (=3). Toroidal field is added as a function of time over a small central region: Adding twists, self-consistently collimate and expand. B flux Kink unstable Time

  21. High Injection Rate Kink unstable

  22. Conclusion: Lessons Learned a) Static limit: • Field lines must “lean” on external pressure, concentrating twists to the central region --- collimation. b) Impulsive injection limit: • Expansion is fast, reducing the toroidal field per unit height. • Velocity difference between the base and the head causes the head to undergo 3D kink, forming a fat head --- lobes (?). c) Continuous injection: • Non-uniform twist distribution along height. • Map out the dependence on injection rates. In all cases, external pressure plays an important “confining” role, helping collimation and stability.

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