Presentation on theme: "Global Simulations of Astrophysical Jets in Poynting Flux Dominated Regime Hui Li S. Colgate, J. Finn, G. Lapenta, S. Li Engine; Injection; Collimation;"— Presentation transcript:
Global Simulations of Astrophysical Jets in Poynting Flux Dominated Regime Hui Li S. Colgate, J. Finn, G. Lapenta, S. Li Engine; Injection; Collimation; Propagation; Stability; Lobe Formation; Dissipation; Magnetization of IGM
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.
Mimicking BH-Accretion System? : Initial poloidal fields on disk, exponential drop-off f( ) : B profile, or disk rotation profile : toroidal/poloidal flux ratio JxB : radial pinching and vertical expansion J p xB p : rotation in direction, carrying angular momentum? =5 =0.1 =3 Li et al.05 Problems: No disk dynamics Footpoints allowed to move, though could be in equilibrium Not precisely Keplerian Mass loading? Dipole or Quadrupole
Injection 1)An initial state modeled as a magnetic spring ( =3). 2)Toroidal field is added as a function of time over a small central region: 3)Adding twists, self-consistently collimate and expand. 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
II. Collimation; Propagation Run A: impulsive injection, =50 v inj >> v A > c s Run B: continuous injection, =3, =3 v A > c s, scanning through (v inj )
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 ?
radius height Pressure Evolution In Implusive Injection Case
Continuous Injection 1)An initial state modeled as a magnetic spring ( =3). 2)Toroidal field is added as a function of time over a small central region: 3)Adding twists, self-consistently collimate and expand. Time B flux Kink unstable
Conclusion: Lessons Learned Field lines must lean on external pressure, concentrating twists to the central region --- collimation. a) Static 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 (?). b) Impulsive injection limit: 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.