Computer Science – Sound
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.7205p&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #72.05; Bulletin of the American Astronomical Society, V
Computer Science
Sound
Scientific paper
Jets, either in AGNs, microquasars or gamma-ray bursts, may be flows of strongly magnetized, low beta (i.e.the ratio of sound speed cs to Alfvén speed vA is small), rotating plasmas. Effective excitation of MRI requires weak magnetic field because the tension of the strong, bent magnetic field would prevent MRI. Nevertheless, we embark on a study of MRI-like instabilities in strongly magnetized plasmas. A cylindrical jet with helical magnetic field and axial and rotational flows is considered. The perturbations do not bend magnetic field lines in the vicinity of resonant surfaces where k|| =0. We show that the shear flow localized to a resonant surface can drive localized unstable modes similar to the pressure driven Suydam modes in laboratory plasma devices (see Bondeson, Iacono, Bhattacharjee, 1987). Rotational flows with the angular velocity Ω can drive both the resonant compressible mode, when r2 dΩ/dr = cs, and MRI-like resonant mode, when r2 dΩ/dr = vA. Sheared axial flow u drives a compressible unstable mode when r du/dr cs. The interval of unstable values of du/dr is narrow. If the flow is ideally stable, slow resistive instabilities driven by sheared flow become important, although they are, probably, too slow to have time to develop in convective jets. This research was supported by the Center for Magnetic Self-Organization for Laboratory and Astrophysical Plasmas at the University of Wisconsin-Madison.
Mirnov Vladimir V.
Pariev Vladimir I.
Prager Stewart C.
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