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Title: Stability Properties of Magnetic Tower Jets

Authors:
; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1211804
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 656; Journal Issue: 2
Country of Publication:
United States
Language:
English

Citation Formats

Nakamura, M, Li, H, and Li, ST. Stability Properties of Magnetic Tower Jets. United States: N. p., 2007. Web. doi:10.1086/510361.
Nakamura, M, Li, H, & Li, ST. Stability Properties of Magnetic Tower Jets. United States. doi:10.1086/510361.
Nakamura, M, Li, H, and Li, ST. Tue . "Stability Properties of Magnetic Tower Jets". United States. doi:10.1086/510361.
@article{osti_1211804,
title = {Stability Properties of Magnetic Tower Jets},
author = {Nakamura, M and Li, H and Li, ST},
abstractNote = {},
doi = {10.1086/510361},
journal = {Astrophysical Journal},
number = 2,
volume = 656,
place = {United States},
year = {Tue Feb 20 00:00:00 EST 2007},
month = {Tue Feb 20 00:00:00 EST 2007}
}
  • Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch models, magnetic fields dominate only at scales {approx}< 100 engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models,more » the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform three-dimensional ideal magnetohydrodynamic adaptive mesh refinement simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.« less
  • Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch models, magnetic fields dominate only at scales <~ 100 engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models,more » the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform three-dimensional ideal magnetohydrodynamic adaptive mesh refinement simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Here, unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.« less
  • We present results of high energy density laboratory experiments on the production of supersonic radiatively cooled plasma jets with dimensionless parameters (Mach number {approx}30, cooling parameter {approx}1 and density contrast {rho}j/{rho}a {approx}10) similar to those in YSO jets. The jets are produced using two modifications of wire array Z-pinch driven by 1MA, 250ns current pulse of MAGPIE facility at Imperial College London. In the first set of experiments the produced jets are purely hydrodynamic and are used to study deflection of the jets by the plasma cross-wind, including the structure of internal oblique shocks in the jets. In the secondmore » configuration the jets are driven by the pressure of the toroidal magnetic field and this configuration is relevant to the astrophysical models of jet launching mechanisms. Modifications of the experimental configuration allowing addition of the poloidal magnetic field and angular momentum to the jets are also discussed. We also present three-dimensional resistive magneto-hydrodynamic (MHD) simulations of the experiments and discuss the scaling of the experiments to the astrophysical systems.« less
  • The evolution of laboratory produced magnetic jets is followed numerically through three-dimensional, nonideal magnetohydrodynamic simulations. The experiments are designed to study the interaction of a purely toroidal field with an extended plasma background medium. The system is observed to evolve into a structure consisting of an approximately cylindrical magnetic cavity with an embedded magnetically confined jet on its axis. The supersonic expansion produces a shell of swept-up shocked plasma that surrounds and partially confines the magnetic tower. Currents initially flow along the walls of the cavity and in the jet but the development of current-driven instabilities leads to the disruptionmore » of the jet and a rearrangement of the field and currents. The top of the cavity breaks up, and a well-collimated, radiatively cooled, 'clumpy' jet emerges from the system.« less